# Do larger rotor sizes really improve braking? - 160 vs 180 vs 185 vs 203 etc



## solidfish (Jul 1, 2012)

It seems to be the general thought that larger rotors equals better braking. I am curious if any company or person has ever tested this on mountain bikes and provide proving data?

I ask because in performance cars, the same question is often asked.

Does larger rotors provide better braking?

For cars, larger rotors do not improve your braking distance. Larger rotors provide better cooling when under intense braking.

Stoptech, a reputable performance car brake company, performed tests on a Nissan 350z using different rotor sizes. Their results and data can be found here:
Testing Brakes with StopTech

They found that smaller rotors stop the car just as quickly as the larger rotors. The only time the larger rotor out performed the smaller rotor was under repeated high speed braking, reaching temperatures over 800 degrees Fahrenheit. But even in these conditions, the largest of rotors gave nearly negligible benefits.

Being that mountain bike brakes use similar compositions as cars (Semi metallic pads / steel rotors), I'm curious:

About what temperatures do our rotors reach in the intense of intense downhills?

And are those temperatures high enough that a larger rotor's better cooling would provide noticeable performance gains?


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## solidfish (Jul 1, 2012)

Perhaps another way to state the question is - how many riders experience brake fade and does larger rotors mediate the problem? 

I dont mean to hint an answer at my own questions, but in cars, if you have brake fade you upgrade to better pads made from material with higher operating temperatures...


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## clunkklonk (Jan 26, 2013)

It's not just the absolute performance. Larger rotors need less pad pressure to achieve the same stopping force. That means less force on the lever as well. That is probably felt as greater control too.


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## Cotharyus (Jun 21, 2012)

This isn't scientific evidence, but if you'll take the word of a guy who has been riding bikes for 30 years, knows a fair amount about cars, particularly from a track performance aspect, and is pretty good at physics:

I spent long enough not mountain biking due to a back injury, that because of a lack of disc brakes on road bikes, my SS 29er was the first bike I bought that had disc brakes. It came with 160mm rotors front and back, which is not unusual. I weigh about 205, and I have to tell you, while I could get enough power from the rear brake to lock it up (I know, that's not ideal, but it indicates that the brake can exceed the traction on that wheel, which I'll get to in a minute) the front brake left a LOT to be desired, and while I never experienced brake fade (hills here aren't big enough) I simply never felt the bike stopped with enough authority. I'd put my weight as far back as I could, and clamp all the way down on the front brake, and get everything I could out of the rear without locking it up, and it was still just kind of an "ok, I'll stop" sort of reaction.

So I changed the front to a 180mm rotor. At that point, I was able to lock the front wheel up as well. From then on, getting all I could out of both brakes resulted in an immediate and authoritative sort of stop. So lets leave brake fade alone for a moment and talk about weight, traction, and leverage.

The only way to alter the results of the test those guys did with the Z is to disable anti-lock on the car, and find a set of rotors so small that the brakes are incapable of locking up the tires. At that point, anything larger (more capable of locking up the tires) will stop the car faster. The larger you get, the less force you have to exert to get the maximum (ie traction limited) braking out of the car, or bike. This goes for two things. Arguably, the most important on the bike is rider fatigue. If you have to work at your maximum effort to get the bike to slow down at it's maximum rate for the conditions, you're going to wear out faster than if you can modulate some lesser amount of effort to achieve the same results - meaning larger rotors are providing an advantage at that point.

Now then, this is where you can take of leave some of this - not because the physics are sketchy, but because I honestly don't know how many people have a problem with this outside of pro-downhillers. Most brake fade is a result of the brake fluid becoming too hot, and boiling. Yes, the larger rotor dissipates heat better than the smaller one, but how much does rotor cooling affect the caliper? Lets assume for the time being that it simply doesn't affect it at all. Why would you use a larger rotor to avoid boiling brake fluid? It goes back to applied force. The same braking force can be achieved with less fluid force in the braking system. This does two things. First, fluids boiling point is raised by being under pressure. So the more pressure you're putting on your brake fluid....the less easily it boils when your caliper gets hot. Second, even if the fluid does reach that point, in theory, if you use 45% effort to lock the tires under a certain condition, so lets say 43% effort is max braking capability, the fluid boils so you lose some effectiveness. Now it requires 88% effort to lock the tires, but you can still do it. Now mind, those numbers are hypothetical, but the increase in fluid pressure should help alleviate the boiling situation, but the point is, you still have brakes, and until the fluid boiled, you were using less effort than it would have taken with a smaller rotor, and I'm not certain the additional pressure used with the smaller rotor would have eliminated the boiling issue. 

Not sure I've overlooked anything, and I hope it answers some questions. Comments or questions about it are welcome, I just sort of off the cuff'd this for an answer, but as far as I'm aware the physics are good. So for what it's worth..there it is. I do think there is an advantage, to a point, in certain conditions, to larger rotors.


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## thomllama (Oct 3, 2007)

ummm I didn't read thru the whole article, but the last little chart shows an obvious improvement with the larger rotors... taking 5 ft off the stoping distance. 5 feet in a car can be the difference between a minor hit if any, and wearing someone's bumper as braces.


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## bulerias (Oct 16, 2012)

Thermal radiating surface of a 200mm rotor is over 50% larger than a 160 rotor. It's hard to get a pad to cool with infra red radiating metal next to it, even by pumping the brakes. So, in theory you should get only two thirds the rotor temp rise rate with a 200 than a 160. Pie are squared.

I have the much maligned Elixir [mine work great; it IS possible!] with a 160 on the front and haven't found power a limitation; that said, when my rotor dies I'll go 180, more for the heat than the leverage.


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## bikeabuser (Aug 12, 2012)

clunkklonk said:


> It's not just the absolute performance. Larger rotors need less pad pressure to achieve the same stopping force. That means less force on the lever as well. That is probably felt as greater control too.


And this information comes from where ?


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## clunkklonk (Jan 26, 2013)

bikeabuser said:


> And this information comes from where ?


Simply by understanding leverage and experience with different rotor sizes on the same bike.

I'd love to be corrected if I'm wrong.


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## bikeabuser (Aug 12, 2012)

clunkklonk said:


> Simply by understanding leverage and experience with different rotor sizes on the same bike.
> 
> I'd love to be corrected if I'm wrong.


apply your understanding to the idea that without increasing pad area, or leverage, I find your claim unbelievable.

I mean really,
You're basically saying that a shop vise has greater clamping force versus handle torque exerted, because you put a bigger piece of sheet metal in it.


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## clunkklonk (Jan 26, 2013)

bikeabuser said:


> apply your understanding to the idea that without increasing pad area, or leverage, I find your claim unbelievable.
> 
> I mean really,
> You're basically saying that a shop vise has greater clamping force versus handle torque exerted, because you put a bigger piece of sheet metal in it.


Think of the rotor as a lever. A 160mm rotor would be a 80mm lever just as a 180mm would be 90mm. The metal sheet is the lever.

EDIT:
And ofcourse, you need less force with a longer lever.


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## bikeabuser (Aug 12, 2012)

clunkklonk said:


> Think of the rotor as a lever. A 160mm rotor would be a 80mm lever just as a 180mm would be 90mm. The metal sheet is the lever.


You're still dealing with a given surface area, and the friction it can induce.

If it's as simple as you say, we'd all have stayed with better materials on canti brakes.


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## clunkklonk (Jan 26, 2013)

bikeabuser said:


> You're still dealing with a given surface area, and the friction it can induce.
> 
> If it's as simple as you say, we'd all have stayed with better materials on canti brakes.


The amount of friction should be the same, but since the braking surface of the larger rotor is travelling at greater speeds it needs less friction to transfer the same amount of energy. Or maybe my understanding of the subject is limited...


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## bikeabuser (Aug 12, 2012)

clunkklonk said:


> The amount of friction should be the same, but since the braking surface of the larger rotor is travelling at greater speeds it needs less friction to transfer the same amount of energy. Or maybe my understanding of the subject is limited...


The amount of friction doesn't change.
The pad size hasn't changed, even if the rotor surface travels past it quicker.

And your torque arm that you mentioned will impart more stopping torque into the hub, spokes, and rim when stopping ... It's all about trade-offs.

I guess that's why Erik Buell mounted his disc brake directly to the rim, on the last versions of his motorcycle ... He saw the flaw in just going bigger


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## One Pivot (Nov 20, 2009)

Larger pads dont equal more braking force, this has been very covered and well proven. You have a fixed amount of force coming off your caliper for a given input from the lever, a larger pad distributes that force over a larger area, so each sq/mm of the pad is exerting less pressure on the rotor.

Think about poking yourself with a needle with 10 pounds of force... its going to stab right through you. If you poked yourself with a 2 inch diameter metal rod with 10 pounds, its not going to do much. Its the same 10 pound force, but the larger diameter rod distributes that same force over a larger area.

If the needle and rod had the same coefficient of friction and were used against a rotor, you'd have the same stopping force since the same total pressure is applied as a clamping force. 

Larger brake pads are used for heat management and longer wear. Bigger pads are a good thing, but its not so much about power.

Disc brakes have MASSIVELY more clamping force than rim brakes. If you had a wheel sized rotor and mounted an average bike brake caliper on it, you'd have no modulation. The lightest touch of the lever would lock the brakes up. 

Clunkkolnk is spot on. 

Larger rotors give more power. A weak brake with a 203 has quite a bit of power. More powerful brakes means you're squeezing less hard with your hand, and less fatigue/hand pump. Modulation plays a big role as well and is a primary focus of mtb brakes (balancing power and modulation).


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## Uphill=sad (Dec 8, 2011)

bikeabuser said:


> I guess that's why Erik Buell mounted his disc brake directly to the rim, on the last versions of his motorcycle ... He saw the flaw in just going bigger


That's an interesting example, the Buell only had a single disc mounted on one side, I'll wager once you measure out the rotor size and divide it by two (since every every other streetbike has a twin disc setup) it'll work out very similar in leverage and surface area. My neighbor owned a Buell, I owned a Hornet, both very similar brake performance - albeit with a visually different approach.

Secondly Buell was known for edging design that stood out from the crowd, i wonder how much was based off unique looks and not a performance increase? It's a shame they are no longer available, cool bikes.


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## ghettocop (Jul 26, 2011)

Real world results for the OP instead of scientific argle-bargle above. I weigh 240 lbs, and ride a hardtail. Started with 160's and moved up to 185's. Much better stopping power. Less fade. Can run 5-6 mile downhill grades with far less fade.


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## 411898 (Nov 5, 2008)

Here's my simple data from experience. My local workout loop finishes up with a 3 miles downhill blast with a 1600' elevation loss. I was experiencing brake fade and black, burned rotors front and rear using 160s going down that hill. I bumped up the front to a 180. Now more fade (equates to more stopping power) on the system (at least a lot less) and no more burned front rotor. However, the rear 160 rotor (recently changed for a new one) is already burned up. I may end up going with a 180 in the rear also. For comparisons, my bike weighs 25.76lbs, and I weigh 171lbs.


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## solidfish (Jul 1, 2012)

Cotharyus said:


> Most brake fade is a result of the brake fluid becoming too hot, and boiling. Yes, the larger rotor dissipates heat better than the smaller one, but how much does rotor cooling affect the caliper?


I agree with your points. Though, I think fluid boiling is not brake fade, that's actually complete brake failure because the brakes will not be able to engage. To remedy this, you would use a higher threshold fluid (ie DOT 5 or 6).



thomllama said:


> ummm I didn't read thru the whole article, but the last little chart shows an obvious improvement with the larger rotors... taking 5 ft off the stoping distance. 5 feet in a car can be the difference between a minor hit if any, and wearing someone's bumper as braces.


Under normal braking, the larger rotors decreased stopping distance by less than 1 foot. That is about .8%, which I would consider less than their margin of error.

Under intense braking, the larger rotors gave better performance, decreasing the distance by about 2.4%.

So, as the original question stated, it seems larger rotors give best gains under intense braking only.


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## solidfish (Jul 1, 2012)

As the second post stated - for those who were having brake fade or brake problems, have you consider upgrading the pad composition? When racing cars, the brake pads are often upgraded before the rotors. Are there mountain bike brake pads with higher temperature thresholds to prevent brake fade?


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## Guest (Feb 25, 2013)

Uphill=sad said:


> That's an interesting example, the Buell only had a single disc mounted on one side, I'll wager once you measure out the rotor size and divide it by two (since every every other streetbike has a twin disc setup) it'll work out very similar in leverage and surface area. My neighbor owned a Buell, I owned a Hornet, both very similar brake performance - albeit with a visually different approach.
> 
> Secondly Buell was known for edging design that stood out from the crowd, i wonder how much was based off unique looks and not a performance increase? It's a shame they are no longer available, cool bikes.


that was the extent of Buell. the rim mounted disc served no advantage over the tried and true dual front on modern sportbikes, HD's and the like perhaps.
Actually it's a major blessing in disguise the buell movement is squashed, just another hidious non functional pile.


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## Ridnparadise (Dec 14, 2007)

I've only ever used sintered pads. In the last 5 years I went from 160 to 180 on the front to gain more intense braking and it worked. In general use there is no difference, but if I need max brakes there is. We don't have massive descents here, but it is always warm to hot. I have ridden pretty solid descents (not DH tracks) in temps over 40C. However, in 99.9% of downhills I have ridden heat has not challenged my brakes. The only time I lost control of my brakes was due to my failure to change the fluid/bleed for too long.

It's a good question OP, but what I really want to know is will larger rotors pull more chicks?:thumbsup:


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## Guest (Feb 25, 2013)

Ridnparadise said:


> I've only ever used sintered pads. In the last 5 years I went from 160 to 180 on the front to gain more intense braking and it worked. In general use there is no difference, but if I need max brakes there is. We don't have massive descents here, but it is always warm to hot. I have ridden pretty solid descents (not DH tracks) in temps over 40C.


This about mimics my experience when switching to a 180 F. Given the relatively same lever pressure It was an instant 'stop now' eye opener so i had to practice modulating lever pressure on extended DH decents and eventually became comfortable.


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## jeffscott (May 10, 2006)

I had a 160 mm Shimano Centerlock floating rotor....I cooked several times going down long hills....on Mauna Kea they fadded so bad I thought I was going to eat it big time..when I got stopped (by stabbing the brakes off and on)....there was a great deal of smoke coming off the pads.

So then I got a 203 Shimano Centerlock floating rotor....I have not cooked the brake yet, and don't think I ever will.

That is what bigger rotors are for.


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## edubfromktown (Sep 7, 2010)

ghettocop said:


> Real world results for the OP instead of scientific argle-bargle above. I weigh 240 lbs, and ride a hardtail. Started with 160's and moved up to 185's. Much better stopping power. Less fade. Can run 5-6 mile downhill grades with far less fade.


Opposite real world results here: I weigh 195 lbs. and went from 185 to 160 rotor up front because I could endo if I hit the front brakes hard with all the stopping power of 185's (particularly on Juicy 7 brakes, I also have Elixir CR's (which go on FR and some DH trails) & BB7's that aren't quite as grabby though I run 160's on them too). 160's give me plenty of stopping power on long descents and no massive fading.


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## bikeabuser (Aug 12, 2012)

Without factoring in all the other variables, stating a bigger rotor is better, is an ego inflating/deflating myth.

Surface area of pads, pad composition, rotor composition, actuation device (cable/hydraulic), mechanical advantage at lever, thermal mass of caliper, heat dissipation characteristics of various components within the system ... What else have I forgotten ?


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## Guest (Feb 25, 2013)

nothing ego or myths on my end just enjoy a superior setup with 180 FACT!!


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## Fachiro1 (Nov 25, 2012)

I'm prettty sure a larger rotor does make a difference, but I also think it depends on the actual brakes themselves. I ran Formula RX's for a few months with 160 rotors front and rear then switched to180/160. The 180 on the front made a difffence, just felt more firm, was easier to lock up, and didnt fade/squeal as much as the 160. Recently I switched from the Formulas to Shimano XT's running 160's front and rear, and they feel just as powerful as the 180/160 Formulas, with no fade and no squeal. This is a 240 pound rider with a 30 pound bike.


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## edubfromktown (Sep 7, 2010)

bikeabuser said:


> Without factoring in all the other variables, stating a bigger rotor is better, is an ego inflating/deflating myth.
> 
> Surface area of pads, pad composition, rotor composition, actuation device (cable/hydraulic), mechanical advantage at lever, thermal mass of caliper, heat dissipation characteristics of various components within the system ... What else have I forgotten ?


If you read what I posted: a smaller rotor works better for me.

I replied to real world observation... which is precisely what I was talking about as well: replaced 185's with 160's on the front of two of my 29er's and observed that 1) they don't throw me over the handlebars when I hit the front brake hard and 2) I have plenty of braking power for long descents.

I didn't need to go into physics calculation mode or break out my old slide rule or HP scientific calculator to verify my findings.


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## solidfish (Jul 1, 2012)

bikeabuser said:


> Without factoring in all the other variables, stating a bigger rotor is better, is an ego inflating/deflating myth.


This is why I asked if any company or group has tried performance testing brakes to backup these claims with data. I understand a lot of people have real world testimony, but it would be nice if like Stoptech, some company can just take a handful of different brakes, get out in a controlled environment, and just start recording data...


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## Saul Lumikko (Oct 23, 2012)

A larger rotor has larger leverage, so it is more effective at stopping the wheel.

Don't believe me? Spin a wheel in a stand and stop it by putting your finger into the spokes at the rim. Then spin it again and put your finger into the spokes near the hub. (Seriously, don't do this because you'll hurt yourself. This should be obvious.)

Because a large rotor requires less input from the lever to lock up, the modulation is reduced. You start to brake by pulling the lever, initially there's just some slack. You increase pressure on the lever to pad contact -> slight braking. Add pressure -> more braking. Finally, lock up. If you have a large rotor, the lock up will happen sooner (at a lower pressure on the lever) compared to a small rotor.

The stock rotors on my Prophet were 160 mm. For a long time it was fine, I wasn't riding that hard. When building a 29er I figured the larger wheels would benefit from larger rotors, so I put 185 mm front and rear. That's when I started thinking about balance between front and rear: the 29er rear was locking up really easily with just one finger on the lever. Since I don't like destroying trails, I switched the 185 mm to the front of my Prophet and put the old 160 mm rotor in the rear on the 29er. Now the rear brake lever required more force to produce a lock up, so I had greater modulation for the rear brake. Also, since developing as a rider, I started going harder on the Prophet and definitely enjoy the increased braking power at the front. 

I'm still not riding long enough downhills to require larger rotors for heat dissipation, nor is my traction good enough to require more braking power. The wheels lock up far sooner than my fingers get tired of pulling the levers so the 185/160 front/rear works fine for me. On my Moonlander I have 160/160 and both brakes seem far less powerful - the tires are larger and have more traction - but I don't ride it that aggressively so it doesn't matter.


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## Mtn-Rider (May 21, 2010)

What I had with 160mm rotors was more than brake fade. On steep, extended downhills I've had my brakes completely vanish. Fortunately never both front and rear at the same time. The rotor arms have a permanent dark fade from overheating.

With a 203mm front rotor and 185mm rear, they don't overheat no matter how hard I try. The brakes feel more reliable overall with large rotors.


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## Reelchef67 (Aug 21, 2011)

bikeabuser said:


> And this information comes from where ?


 Basic physics.
Larger rotors act a larger lever arm.
The wheel radius is one lever, the disc radius is the 2nd lever
The axle is the is fulcrum. 
Therefore a larger rotor will have more leverage = more power from the longer lever .
IE The 90mm lever of a 180 compared to 80mm lever of a 160.
Its not rocket science.

And as a byproduct of greater surface area it stays cooler =less brake fade.


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## authalic (Apr 8, 2005)

bikeabuser said:


> And this information comes from where ?


There is a whitepaper on the Stoptech site that the OP mentioned. It's called "The Physics of Braking Systems". The section on The Rotor says the torque generated by the rotor is a function of the frictional force from the pads multiplied by the effective radius of the rotor.

http://www.stoptech.com/docs/media-center-documents/the-physics-of-braking-systems

To generate the same amount of torque at the hub, a rotor with a larger radius would require less frictional force from the pads.

What I'm still a bit fuzzy on, is whether the faster velocity of the braking surface passing through the pads on a larger rotor would generate more friction force under the same pressure from the pads than on a smaller rotor.

If that's the case, then you would need less pressure from the pads to generate the same friction force on a larger rotor than on a rotor with a smaller radius spinning at the same angular velocity, and you would need less friction force on the rotor to generate the same torque at the hub. So, both ways, you're using less force at the lever with a larger rotor.... right?


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## drifter248 (Nov 1, 2011)

Velocity has very little effect on the coefficient of friction. Temperature, on the other hand, has a rather large effect. The coefficient of sliding friction between the brake pads and rotor decreases as temperature increases, which contributes to the dreaded brake fade. The pressure applied to the rotor by the brakes pads will be the same regardless of the size of the rotor, assuming both are operating at the same temperature. The larger rotor, however, will generate more braking torque than a smaller rotor when applying the same pressure to the brake lever. Braking torque is equal to the (coefficient of sliding friction) x (contact pressure between rotor and brake pads) x (radius from the wheel axle to the brake pads). A 180mm rotor produces approximately 12.5% more braking torque than a 160mm rotor.


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## solidfish (Jul 1, 2012)

authalic said:


> There is a whitepaper on the Stoptech site that the OP mentioned. It's called "The Physics of Braking Systems". The section on The Rotor says the torque generated by the rotor is a function of the frictional force from the pads multiplied by the effective radius of the rotor.
> 
> http://www.stoptech.com/docs/media-center-documents/the-physics-of-braking-systems


+1

Thanks for that reference. Here is a quote directly from that paper:



> While the rotor serves as the primary heat sink in the braking system, it is the functional responsibility of the rotor to generate a retarding torque as a function of the brake pad frictional force.
> 
> This torque is related to the brake pad frictional force as follows:
> Tr = F(friction) × R(eff)
> ...


Using basic equality rules, I rewrite their function as follows:

F(friction) = Tr / R(eff)
• F(friction) is the frictional force required by caliper and pad to stop
• Tr is the torque, generated not only by the rotor, but a combination of rotor + wheel + tire + etc.
• R(eff) is the radius, or the size of the rotor

*So based on this function, it tells us that as R(eff) approaches infinity, F(friction) approaches zero. In other words, larger rotors requires less Frictional force by the pads.*

Someone please correct me if my math/logic is wrong here.

I would highlight this statement from the paper though:


> ...the rotor serves as the primary heat sink in the braking system...


Although a larger rotor could reduce the F(friction) required by the brake pads, that is not its primary purpose. If one wanted to increase braking, they should focus more on the pads or calipers to something that generates more frictional force.


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## solidfish (Jul 1, 2012)

^ So mathematically it makes sense. Would still be nice if someone could real world test this with a yard stick to see exactly how much improvement it has.


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## bulerias (Oct 16, 2012)

solidfish said:


> ^ So mathematically it makes sense. Would still be nice if someone could real world test this with a yard stick to see exactly how much improvement it has.


A bigger rotor won't stop you any faster unless it's incapable of locking the wheel. But it will require less lever pressure - given no other changes - and do it more times in a row before overheating. The real world actually operates on mathematics so you can just accept it; that's why nobody bothers to test it in the 'real world'. Levers are levers and surface area counts. The improvements are proportional, as usual.

That said, it would be nice to know how linear the relationship of temperature to C of Friction is. My guess is that there would be a rather steep drop off at some point.


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## authalic (Apr 8, 2005)

solidfish said:


> ^ So mathematically it makes sense. Would still be nice if someone could real world test this with a yard stick to see exactly how much improvement it has.


There is this engineering paper, about some lab results from a test bench that the authors built to test disc brakes on bikes.

http://www.sensorprod.com/news/white-papers/2010-03_ctb/wp_ctb-2010-03.pdf

If you scroll down to the last page, there is a graph showing the brake force generated by 3 different rotors as the hand force increases. Here's a quote from the summary:



> The model was tested with three different types of brake discs, varying in diameter and geometry of the friction ring. ... the only significant differences between the three functions are as expected the rise of the function and the maximum reached brake force.


It helps to see the graph.


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## Uphill=sad (Dec 8, 2011)

bulerias said:


> A bigger rotor won't stop you any faster unless it's incapable of locking the wheel. But it will require less lever pressure - given no other changes - and do it more times in a row before overheating. The real world actually operates on mathematics so you can just accept it; that's why nobody bothers to test it in the 'real world'. Levers are levers and surface area counts. The improvements are proportional, as usual.


Being able to lock up a wheel is not necessarily an indicator that one brake is better than another brake, all brakes can do this (or should be able to). A skidding wheel provides poor braking performance, hence the advent of ABS on modern cars. Personally I find the more powerful the brake the harder I can brake before the wheel locks up, as long as the brake has decent modulation.

The only other thing no one has mentioned is a larger rotor will tend to be a bit more grabby at slow speeds, I run 203 on the front and at very slow trail speeds during technical riding it can be a challenge to control at times (lack of modulation), when the speed picks up it's great.


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## bikeabuser (Aug 12, 2012)

Uphill=sad said:


> Being able to lock up a wheel is not necessarily an indicator that one brake is better than another brake, all brakes can do this (or should be able to). A skidding wheel provides poor braking performance, hence the advent of ABS on modern cars. Personally I find the more powerful the brake the harder I can brake before the wheel locks up, as long as the brake has decent modulation.
> 
> The only other thing no one has mentioned is a larger rotor will tend to be a bit more grabby at slow speeds, I run 203 on the front and at very slow trail speeds during technical riding it can be a challenge to control at times (lack of modulation), when the speed picks up it's great.


The mathmaticians will say you are wrong ... Bigger is ALWAYS better


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## kapusta (Jan 17, 2004)

bikeabuser said:


> Without factoring in all the other variables, stating a bigger rotor is *better*, is an ego inflating/deflating myth.


Better? OK, that is subjective. However, they DO require less frictional force from the pads (and therefore force on the brake lever) to generate a given amount of stopping force. That's not a myth, that's just a fact. Simple physics, actually


> Surface area of pads, pad composition, rotor composition, actuation device (cable/hydraulic), mechanical advantage at lever, thermal mass of caliper, heat dissipation characteristics of various components within the system ... What else have I forgotten ?


You can change those around all you want, but whatever pad/rotor/actuation/lever/caliper combo you can come up with, swapping a smaller rotor for a similar one of larger diameter (with apropriate adaptor for the caliper) is going to give your mor estapping power for a given amount of force at the lever.


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## solidfish (Jul 1, 2012)

Uphill=sad said:


> Being able to lock up a wheel is not necessarily an indicator that one brake is better than another brake, all brakes can do this (or should be able to). A skidding wheel provides poor braking performance





authalic said:


> There is this engineering paper, about some lab results from a test bench that the authors built to test disc brakes on bikes.
> 
> http://www.sensorprod.com/news/white-papers/2010-03_ctb/wp_ctb-2010-03.pdf


Great find! I think this is about as close to real world tests for mountain bikes. Their findings show that larger rotors just lessen the lever pressure required to stop. It actually just proves my post from above based on the function and tests given by Stoptech.

So - based on these articles - it seems safe to say that *larger rotors does not improve braking directly. Instead, it just alleviates the brake lever force (and improve cooling).* This is why it is easier to lockup the brakes on larger rotors. And as Uphill stated above, locking up your brakes easily doesnt mean you have higher performing brakes. The lockup is actually detrimental.


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## 411898 (Nov 5, 2008)

Is this to say that braking with a larger rotor compared to a smaller rotor is also going to extend pad life when used on the same terrain at the same intervals?


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## Uphill=sad (Dec 8, 2011)

bikeabuser said:


> The mathmaticians will say you are wrong ... Bigger is ALWAYS better


I certainly do agree with that as a stand alone statement, larger rotor = larger moment arm.

But, if there is a loss of brake modulation due to the larger moment arm, there will also be a loss in brake performance as is becomes harder to find that perfect friction point before the tire breaks free and hence a loss in performance especially in loose gravel or muddy/slippery conditions.

This is the reason why many WC DHer's are not using 203mm rotors on the rear.


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## Jon Richard (Dec 20, 2011)

bikeabuser said:


> Surface area of pads, pad composition, rotor composition, actuation device (cable/hydraulic), mechanical advantage at lever, thermal mass of caliper, heat dissipation characteristics of various components within the system ... What else have I forgotten ?


Mechanical advantage at the wheel and thermal capacity of the rotor.

It's not a question of better, everything is a compromise. A larger rotor will require less lever force and cope with sustained periods of braking longer but will have less modulation and weigh more.


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## clunkklonk (Jan 26, 2013)

You get the same amount of modulation with larger rotors. The force needed at the brake lever is just less. A underpowered brake will be easier to modulate at the bite point (or whatever you call it) but it will be tricky at the point of wheel lock. I prefer excess power for good control under hard braking.

I used to ride a 29" bike with a 160mm front rotor. It was horrible downhill, even scary. A 180mm was good but still left a desire for something better.

There are big differences in how different pads bite the rotor. Try them out if brake feel is important to you.


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## Mac_Aravan (Nov 22, 2012)

I experiment the lack of modulation when going from 180mm/Hayes9 to 180mm/SLX, SLX are so powerfull that a little touch provides a noticeable breaking power.
I found it difficult to control in low speed situation. Now I am a bit used to it, but mainly the best workaround is to go faster


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## Saul Lumikko (Oct 23, 2012)

clunkklonk said:


> You get the same amount of modulation with larger rotors.


Kind of and kind not.

When using the same levers and calipers, just varying rotor size, it takes the same amount of force on the lever to bring the pads to the disc. From there you gradually increase force until lockup. With a larger rotor lockup happens at a lower force -> the range between pad contact and lockup is smaller. This is the reason why I switched to a smaller rotor in the rear: a very slight increase in the force I used to pull the lever would result in lockup. With a smaller rotor I can increase and decrease force on the lever without going out of useful range (pad contact - lockup) so easily.

On the other hand if the brakes are way underpowered, you need to squeeze the levers really hard to get anything useful out of them, and modulation is difficult when you use proportionally a higher amount of force available. In other words brake modulation is easier for people with stronger hands, even though they are not using everything they have.



clunkklonk said:


> I prefer excess power for good control under hard braking.


This is quite true. If I can't lock both ends with just one finger, the brakes are not powerful enough. Not that I do it normally, but the option must be available. Braking requires delicate finger control and it's easier to modulate power when you don't have to squeeze the levers with your knuckles and joints turning yellow.


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## bikeabuser (Aug 12, 2012)

Jon Richard said:


> Mechanical advantage at the wheel and thermal capacity of the rotor.
> 
> It's not a question of better, *everything is a compromise*. A larger rotor will require less lever force and cope with sustained periods of braking longer but will have less modulation and weigh more.


YEP, you nailed it ... For those who are not hauling butt and doing long downhill sections, a bigger rotor is not necessarily going to be better.
In fact, they are prone to more and greater damage, if riding technical stuff.

Compromise is the key word, and regardless of size, there will be some form of compromise.

A well designed braking system for the riders intended purpose, is much better than a poorly designed, big rotor is better (mythical) system 

I guess that's why most of the trials guys grind their rims, and run what many think are an antiquated system on their rear wheel ... They want/need the lock-up and weight reduction that a disc won't give them.

And lever pressure, is a mechanical advantage thing, that is also based on a compromise.

clunkklonk also nailed a big factor ... Pad and rotor materials.
They both affect the system.

IMO,
The most sophisticated braking system ever designed can be screwed up via improper adjustment, no adjustment, or a bit of oil 
And size won't evercome such basic things.


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## Jon Richard (Dec 20, 2011)

Bikeabuser, the main thing to realize is that my rotors are bigger than yours and therefore I am much cooler than you

What you said about trials riders is exactly right. Those guys need holding power they're not worried about heat dissipation.

An xc rider and a downhill guy will have very different views on what the ideal brake set up is-truth.


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## D.F.L. (Jan 3, 2004)

Related, but not exactly on-topic:

Anybody care to address what rotor speed (swept surface across the pads) means to friction and resulting brake torque?

At high speed, we know that our brakes feel less effective. The rate of negative acceleration is obviously lower at high speed than at low speed. The lever force I use at 25mph would put me over the bars at 5mph. Just as a smokey burnout doesn't give one great acceleration in their car, rotors slipping across pads at higher rates gives diminished results.

So, if that's true, then larger rotors will give away some of their advantage simply because of the higher rate at which they rotate past the pads.

Any thoughts?


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## Ridnparadise (Dec 14, 2007)

Deleted - posted out of sequence


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## Cotharyus (Jun 21, 2012)

D.F.L. said:


> Related, but not exactly on-topic:
> 
> Anybody care to address what rotor speed (swept surface across the pads) means to friction and resulting brake torque?
> 
> ...


Sure. They give away some of the advantage they'd have due to the increase in rate they pass under the pads, but they don't give up as much as they gain in leverage.


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## Mac_Aravan (Nov 22, 2012)

Energy from speed is square of speed ( 1/2 mV²), but your brake can only dissipate a given energy per second. That's why your brake seems less effective, and that's why bigger rotor can help as they can dissipate much more energy


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## bulerias (Oct 16, 2012)

Theoretically, the kinetic coefficient of friction is independent of speed. So whatever force puts you OTB at 5 mph should do the same at 25mph. 

In practice however, engineering cleverness has increased the COF but at the expense of some speed dislinearity. If you had steel surface pads you'd have linearity. So in theory a less grabby pad on a larger disc would give the same power and more predictability plus lower temperatures.


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## Axe (Jan 12, 2004)

Bigger is better.

Said the actress to the bishop.


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## Guest (Mar 2, 2013)

Axe said:


> Bigger is better.
> 
> Said the actress to the bishop.


and the bishop to the pawn


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## Axe (Jan 12, 2004)

nvphatty said:


> and the bishop to the pawn


And getting back to the topic - I do like to have larger rotor in front. Seem to be easier to control, as I usually use both brakes simultaneously.


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## bikeabuser (Aug 12, 2012)

I like how this thread of opinions has progressed into further opinions


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## kapusta (Jan 17, 2004)

bikeabuser said:


> I like how this thread of opinions has progressed into further opinions


I'm sure that you have contributed something of value in this thread.

I just can't seem to find it.


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## bikeabuser (Aug 12, 2012)

kapusta said:


> I'm sure that you have contributed something of value in this thread.
> 
> I just can't seem to find it.


That's OK


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## ehigh (Apr 19, 2011)

I've been riding on a pair of XTR trail brakes with a 160mm rotor in rear and a 180mm up front for about a year and a half now. I haven't had to replace my front rotor yet, though when I have to I will probably just put a 160mm up front too. I weigh 210 with all my gear, loaded for a day of riding, and I feel that sometimes I could benefit from a 180mm on the rear brake, but by and large it is unnecessary for me.



kapusta said:


> I'm sure that you have contributed something of value in this thread.
> 
> I just can't seem to find it.


Well put.

Sent from my Desire HD using Tapatalk 2


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## Sandrenseren (Dec 29, 2011)

There is just so much wrong information in this thread that it's mind boggling.

The whole lever idea is bonkers for starters. Here's why:

Let's look at a hydraulic brake caliper. No matter what size of disc you run, the caliper stays the same. It doesn't matter to the caliper if it's mounted higher or lower on the fork, it's still same the same caliper. The caliper has no idea what size brake disc you have installed, all the caliper sees is a band of metal moving between it's pads. It doesn't matter to the caliper if the steel going between it's pads are curved into a 160 mm disc, a 180 mm disc or a straight piece of metal being pulled through by a dog. It's all the same to the caliper.

A 180 mm disc is 12.5% bigger than a 160 mm disc so for the same speed of the wheel, the metal in the bigger disc moves 12.5% faster past the brake caliper. To the caliper there is absolutely no difference between a 180 mm disc mounted on a wheel that spins at 20 mph and a 160 mm dish mounted on a wheel that spins at 22.5 mph (12.5% faster than 20 mph) assuming the wheels are the same size. The metal that passes the brake pads are racing past at the same speed in those two situations.

So from the calipers point of view it has no idea if it's looking at a 180 mm disc on a wheel spinning at 20 mph or if it's a 160 mm disc on a wheel spinning 22.5 mph (same sized wheels). The clamping force needed to grab the brake rotor is exactly the same, so forget about the nonsense that bigger discs somehow alters the feel of the brake levers, there is no change at all in brake feel as the caliper is the same and requires the same amount of fluid pumped in to deliver the same amount of clamping force.

Forget about the lever thing too, the caliper can't feel any difference between a big or a small disc, it's all just a strip of metal passing the pads from the calipers point of view.

As for friction it's determined by the choice of materials. What material the pads are and what material the rotors are. As long as the small and big rotor are made from the same material the size doesn't matter, they have exactly the same amount of friction and the same "brake feel"..

The only reason to pick a bigger disc is heat management and the ability to cool down during braking. Once the disc and pads heat up to a certain point the friction between them will dramatically drop and you'll lose brake power. As long as they don't get heated to that point you'll feel absolutely no difference between a big and a small disc, not in stopping power, not in modulation, not in "feel".

Does your current brake system have a lot better modulation and feel if you brake from 22.5 mph rather than 20 mph? No, it's still the same caliper and brake lever. Moving that caliper a bit and fitting a smaller or bigger brake rotor of the same material doesn't change the feel either, still the same caliper and brake lever. Only change is how hot the pads and rotor gets when braking.


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## J.B. Weld (Aug 13, 2012)

Sandrenseren said:


> Forget about the lever thing too, the caliper can't feel any difference between a big or a small disc, it's all just a strip of metal passing the pads from the calipers point of view.


I don't know about that. I have no of the physics involved here and admittedly I can be an idiot at times but if I pretend my forefinger and thumb are a caliper and pinch a 1 inch disc on a spinning wheel to stop it and then pinch a disc the size of the rim on the same wheel I'm pretty sure my fingers could tell a difference between the two.


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## kapusta (Jan 17, 2004)

Sandrenseren said:


> There is just so much wrong information in this thread that it's mind boggling.


You just just topped it all in one post



> The whole lever idea is bonkers for starters. Here's why:


Ummmm, I think you need to understand what a "lever" does.

You are correct in that the caliper does not "know" what size disc it is grabbing. That does not change the fact that it has a greater mechanical advantage (or leverage) on the larger rotor.

The whole point of a lever is that when you increase the input arm length (in this case the rotor radius) relative to the output arm length (the wheel radius), you get a greater output force (braking) for a given input force friction at the pad/rotor interface.

If by "lever" you are strictly talking about the actual brake lever, the larger rotor the feel at the brake lever because it take less force from your finger to generate a given amount of braking force.


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## bikeabuser (Aug 12, 2012)

Sandrenseren said:


> There is just so much wrong information in this thread that it's mind boggling.
> 
> The whole lever idea is bonkers for starters. Here's why:
> 
> ...


Yet we have some people who just can't think outside the box enough to realize this is all true ... And I must admit that your word choice is better than what I have said in many posts.

Perhaps you won't have some butt hurt member negative repping you, while claiming you've contributed nothing, because of your word choice


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## Axe (Jan 12, 2004)

Sandrenseren said:


> There is just so much wrong information in this thread that it's mind boggling.


And you just doubled it.

It absolutely does matter what size rotor you use for the brake feel. Coefficient of friction does not depend much on speed of the rotor. But the torque sure does depend on the rotor diameter, given the same braking force. You would have failed my physics class.


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## kapusta (Jan 17, 2004)

Axe said:


> You would have failed my physics class.


No doubt. Heck, I covered this in an 8th grade physical science class I taught.


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## kapusta (Jan 17, 2004)

bikeabuser said:


> Perhaps you won't have some butt hurt member negative repping you, while claiming you've contributed nothing, because of your word choice


WHAT?!

What the hell are you talking about? I'm the one who implied that you are not contributing, but you know darn well I have not neg repped you. That is an outright lie and you know it!

Weak, just weak.


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## bikeabuser (Aug 12, 2012)

Axe said:


> And you just doubled it.
> 
> It absolutely does matter what size rotor you use for the brake feel. Coefficient of friction does not depend much on speed of the rotor. But the torque sure does depend on the rotor diameter, given the same braking force. You would have failed my physics class.


If you're gonna go all mathematical ... Don't forget to include all the variables that are/can change in a real World change of rotor size.


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## bikeabuser (Aug 12, 2012)

kapusta said:


> WHAT?!
> 
> What the hell are you talking about? I'm the one who implied that you are not contributing, but you know darn well I have not neg repped you. That is an outright lie and you know it!
> 
> Weak, just weak.


I never said it was you ... And I'll not say who, but yea, someone claimed I've contributed nothing, and gave me some Neg 

So while the opinions keep getting tossed around, I'll just restate (in different words) that if it's not a designed system (rotor size/caliper/brake lever) it's just an unfounded claim that bigger is always better.


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## Axe (Jan 12, 2004)

bikeabuser said:


> If you're gonna go all mathematical ... Don't forget to include all the variables that are/can change in a real World change of rotor size.


Actually that is not how you solve physics problems. You isolate factors to simplify the model, and then compare what is important and what is not. Heat dissipation is certainly the biggest factor for extended brake use. (BTW, those IceTech pads and rotors are the real deal IMO.. no fade). Then brake force and modulation - it takes 25% less pressure on the lever for the same deceleration with 203mm rotor than with 160mm, and it is noticeable - with cool rotors.


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## kapusta (Jan 17, 2004)

bikeabuser said:


> If you're gonna go all mathematical ... Don't forget to include all the variables that are/can change in a real World change of rotor size.


Such as what? All you need is a different rotor and a different caliper mount adapter.

But since you bring up real world, why don't you just ask anyone who has actually done this? I have, and it works just as basic physics would predict.

I'm not sure if you are serious, or just trolling at this point.


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## bikeabuser (Aug 12, 2012)

Axe said:


> Actually that is not how you solve physics problems. You isolate factors to simplify the model, and then compare what is important and what is not. Heat dissipation is certainly the biggest factor for extended brake use. (BTW, those IceTech pads and rotors are the real deal IMO.. no fade). Then brake force and modulation - *it takes 25% less pressure on the lever for the same deceleration with 203mm rotor than with 160mm*, and it is noticeable - with cool rotors.


And like I and others have said, that doesn't make them better.

The biggest factor being left out is the rider and their style of riding ... Heck, I even left it out when discussing the design.

A touchy, lock up if you breath on it wrong, brake lever, is a piece of crap system if you ride slow technical stuff ... YES ?


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## J.B. Weld (Aug 13, 2012)

Torque = force x distance- just to confuse the issue with facts.


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## bikeabuser (Aug 12, 2012)

kapusta said:


> Such as what? All you need is a different rotor and a different caliper mount adapter.
> 
> But since you bring up real world, why don't you just ask anyone who has actually done this? I have, and it works just as basic physics would predict.
> 
> I'm not sure if you are serious, or just trolling at this point.


Read post #74, then reflect back to the OP's question.


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## Axe (Jan 12, 2004)

bikeabuser said:


> And like I and others have said, that doesn't make them better.
> 
> The biggest factor being left out is the rider and their style of riding ... Heck, I even left it out when discussing the design.
> 
> A touchy, lock up if you breath on it wrong, brake lever, is a piece of crap system if you ride slow technical stuff ... YES ?


In my garage I do have bikes with 160/160, 180/160, 180/180, 203/160 rotors. It does not make one better than the other, but it does not change the fact that the statement that radius does not matter that I was responding too, and that you so smugly concurred, was absolutely wrong.

I would pick a larger rotor for slow technical stuff. Same reason many observed trials riders still use hydraulic rim brakes. YMMV.


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## kapusta (Jan 17, 2004)

bikeabuser said:


> Read post #74, then reflect back to the OP's question.


Never refer to posts by number. They show up differently depending on viewing settings, and change as more posts get added. I don't even have a #74 in my view setting.

Link to them.


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## bikeabuser (Aug 12, 2012)

Axe said:


> In my garage I do have bikes with 160/160, 180/160, 180/180, 203/160 rotors. It does not make one better than the other, but it does not change the fact that the statement that radius does not matter that I was responding too, and that you so smugly concurred, was absolutely wrong.
> 
> I would pick a larger rotor for slow technical stuff. Same reason many observed trials riders still use hydraulic rim brakes. YMMV.


Like I said ... _rider and their style of riding_


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## kapusta (Jan 17, 2004)

bikeabuser said:


> _rider and their style of riding_


.....does not change the fact that Sandrenseren's post that you agree with is pure nonsense.


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## bikeabuser (Aug 12, 2012)

kapusta said:


> .....does not change the fact that Sandrenseren's post that you agree with is pure nonsense.


Thanks for qualifying post #59 (Opinion) LOL


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## Axe (Jan 12, 2004)

bikeabuser said:


> Like I said ... _rider and their style of riding_


That is not what you said in your response to an incorrect statement.

But apparently you are one of the people who would argue for the sake of arguing. Have at it. But brush up your physics as well.


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## One Pivot (Nov 20, 2009)

Jeez. This is getting painful. Some of you must have never touched a bike with bigger brakes. Its amazingly bizarre that people are even trying to argue this. 

Sandrenseren's post was the longest, most wrong post ive ever seen on a bike forum :lol:


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## bikeabuser (Aug 12, 2012)

One Pivot said:


> Jeez. This is getting painful. Some of you must have never touched a bike with bigger brakes. Its amazingly bizarre that people are even trying to argue this.
> 
> Sandrenseren's post was the longest, most wrong post ive ever seen on a bike forum :lol:











Opinions Vary.


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## One Pivot (Nov 20, 2009)

Yes, opinions vary. Luckily physics doesnt so it makes this conversation pretty easy. Theres no opinions when wondering if a longer lever has more leverage.


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## Haint (Jan 25, 2012)

One Pivot said:


> Yes, opinions vary. Luckily physics doesnt so it makes this conversation pretty easy. Theres no opinions when wondering if a longer lever has more leverage.


Thread Closed.


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## solidfish (Jul 1, 2012)

One Pivot said:


> Yes, opinions vary. Luckily physics doesnt...


+1



Sandrenseren said:


> There is just so much wrong information in this thread that it's mind boggling.
> 
> ...
> 
> The clamping force needed to grab the brake rotor is exactly the same, so forget about the nonsense that bigger discs somehow alters the feel of the brake levers, there is no change at all in brake feel as the caliper is the same and requires the same amount of fluid pumped in to deliver the same amount of clamping force.


For Sandrenseren and those jumping on this train late, may I refer you to the following posts please:

http://forums.mtbr.com/brake-time/d...-vs-185-vs-203-etc-840746-2.html#post10194312

http://forums.mtbr.com/brake-time/d...-vs-185-vs-203-etc-840746-2.html#post10194547

Here is the physics:
F(friction) = Tr / R(eff)
• F(friction) is the frictional force required by caliper and pad to stop
• Tr is the torque, generated not only by the rotor, but a combination of rotor + wheel + tire + etc.
• R(eff) is the radius, or the size of the rotor

As R(eff) gets bigger (larger the rotor size), F(friction) gets smaller (less force required to stop the rotor). Therefore, many people report that with larger rotors, they feel its easier to lockup the wheel.



Sandrenseren said:


> As for friction it's determined by the choice of materials.
> 
> ...
> 
> The only reason to pick a bigger disc is heat management and the ability to cool down during braking.


These points are correct. F(friction) comes from pads, as noted in above equation. Some pad compositions have higher F(friction) values. The equation above shows that if you increase the F value, you can either increase the T(torque) value or even decrease the R(radius) value of the rotor.

But the R(radius) value is directly related to heat dissipation. The smaller the rotor = the less heat you can dissipate. But from what I've read so far, there are not a lot of people here who experience bad brake fade. So it seems that brake fade is not one of the common reasons to increase rotor size.


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## kapusta (Jan 17, 2004)

One Pivot said:


> Yes, opinions vary. Luckily physics doesnt so it makes this conversation pretty easy. Theres no opinions when wondering if a longer lever has more leverage.


Physics is such "_in the box_" thinking :yawn:

We need to start thinking outside the box. You know..... switch up a few function signs.... swap a "force" here for a "diameter" over there. Let's get creative about this.


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## Uphill=sad (Dec 8, 2011)

authalic said:


> It helps to see the graph.


Graph is attached - a little small, oh well.









I wonder why they selected around 80 newtons as the handforce - the paper doesn't really state why. 80n is pretty low, I presume they were braking with only 1-2 fingers (which would be pretty realistic i think....)?


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## Axe (Jan 12, 2004)

Uphill=sad said:


> I wonder why they selected around 80 newtons as the handforce


Sounds about right. 18 pounds weight. Not really small for one finger.


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## Fajita Dave (Mar 22, 2012)

bikeabuser said:


> And like I and others have said, that doesn't make them better.
> 
> The biggest factor being left out is the rider and their style of riding ... Heck, I even left it out when discussing the design.
> 
> A touchy, lock up if you breath on it wrong, brake lever, is a piece of crap system if you ride slow technical stuff ... YES ?


What does rider style have to do with it? If you want more braking power than getting a bigger rotor would be a good way to make it happen. If you don't want more braking power than don't get a bigger rotor. There is a reason why they fit the big rotors on downhill bikes (where you need lots of braking force on every ride), small rotors on XC (where you rarely use the brakes) and mid size rotors on freeride mountain bikes (where you'll probably be needing strong brakes sometimes but not always). The manufactures seem to have this figured out already.

If your brakes are to touchy than choosing a different pad material will most likely fix it.


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## bikeabuser (Aug 12, 2012)

Fajita Dave said:


> *What does rider style have to do with it? *If you want more braking power than getting a bigger rotor would be a good way to make it happen. If you don't want more braking power than don't get a bigger rotor. There is a reason why they fit the big rotors on downhill bikes (where you need lots of braking force on every ride), small rotors on XC (where you rarely use the brakes) and mid size rotors on freeride mountain bikes (where you'll probably be needing strong brakes sometimes but not always). The manufactures seem to have this figured out already.
> 
> If your brakes are to touchy than choosing a different pad material will most likely fix it.


I guess you answered your own question ... Huh ?


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## Haint (Jan 25, 2012)

This still?? 

The lever-action description settles the matter - longer lever means more ability to leverage.

If braking were only a matter of crushing brake levers into grips then the arguement could go on forever and ever. Since brakes sometimes need a quick hit to correct the bike, and sometimes weight is not distributed optimally (that'd be me or you) on the bike - a bigger rotor allows more braking force to be applied.

I hope MBAction does not perform a brake rotor 0-20-0 test in the next issue.


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## Axe (Jan 12, 2004)

bikeabuser said:


> I guess you answered your own question ... Huh ?


You still do not get it? Objective performance of a component has nothing to do with rider style. It performs the same independent of who rides it.


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## jeffscott (May 10, 2006)

Axe said:


> You still do not get it? Objective performance of a component has nothing to do with rider style. It performs the same independent of who rides it.


Not really true....The techniques used by a better rider will change the objective performance of that component....That is why will still have to have the race to find out who wins...

For example take a brake test set up.....the rotor driven by a large flywheel with a certain moment of inertia....clamp the brake lever down to a certain force and mesure the time to stop....

Shoudl be a repeatable reliable test of objective performance...

Now take the same test but allow a inexperienced rider to clamp the brake lever...measure the time to stop...

Then take an experienced rider and let him run the clamp he should have the fastest time to stop of all three tests...

So which test represents the objective performance of the brake...certainly not the simplistic clamp the lever to a certain force...probably no the beginner rider...

Maybe the average of several experinced riders...

Then extend the test to compare differerent rotor systems....with experienced riders....then you might have an realistic and objective test comparison.


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## kapusta (Jan 17, 2004)

This thread is suffering badly from two distinctly different types of arguments getting confused with one another.

1- The first set of arguments have to do with the facts. One is whether bigger rotors are more powerful. Or more specifically, do they give you more stopping force for a given amount of force on the brake lever. This is simple physics, and the answer is yes. Do they cool better? Again, physics would say yes.

2- The OTHER question (the one actually asked in the OP's post) is whether bigger rotors "improve" braking. That is a very subjective question, as it encompasses many things, and shear braking power from a given force on the levers is just one aspect. There are reasons some people choose NOT to run bigger rotors from a performance standpoint. Personally, I found that going from a 160mm rotor in the front to a 203mm made it a little more difficult for me to control in slower and looser situations. I found a 185mm to be the happy medium. Of course, this is just me, someone else (faster, heavier, bigger front tire, who knows) might prefer the 203mm rotor. Also, on a bigger bike, or in an area that had faster DH runs, I would likely go bigger.

So, while personal preference and/or riding style have no effect on the simple physics of going to a larger rotor, it does have an effect on whether bigger is "better".

Then, finally, there are those who seem to feel that simple physics are just another opinion. Not much to discuss there.


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## solidfish (Jul 1, 2012)

kapusta said:


> This thread is suffering badly from two distinctly different types of arguments getting confused with one another.
> 
> 1- One is whether bigger rotors are more powerful.
> 
> 2- The OTHER question (the one actually asked in the OP's post) is whether bigger rotors "improve" braking.


The problem maybe that many people think this is the same question. If bigger rotor has more braking power (by making it easier to brake, ie. requires less force), then it must be "improving" braking.


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## fsrxc (Jan 31, 2004)

bikeabuser said:


> And like I and others have said, that doesn't make them better.
> 
> The biggest factor being left out is the rider and their style of riding ... Heck, I even left it out when discussing the design.
> 
> A touchy, lock up if you breath on it wrong, brake lever, is a piece of crap system if you ride slow technical stuff ... YES ?


Changing rotor size has very little affect on modulation (however you would quantify that). Yes it takes less pressure, so you apply less pressure. For long DH runs it can mean a big reduction in arm pump.


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## Guest (Mar 6, 2013)

the thread that keeps on giving..:lol:


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## Axe (Jan 12, 2004)

jeffscott said:


> Not really true....


Yes, it is really true. Bike weights the same no matter who sits on it. Rotor develop the same braking torque no matter who pulls the lever.


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## Jon Richard (Dec 20, 2011)

fsrxc said:


> Changing rotor size has very little affect on modulation (however you would quantify that). Yes it takes less pressure, so you apply less pressure. For long DH runs it can mean a big reduction in arm pump.


This is a contradictory statement as modulation is synonymous with force attenuation. If less pressure is required to produce the same force then the lever will be more sensitive to inputs.


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## Fajita Dave (Mar 22, 2012)

bikeabuser said:


> I guess you answered your own question ... Huh ?


That has nothing to do with rider STYLE. It has everything to do with what you NEED for the TERRAIN that your riding. If your riding downhill than you NEED stronger brakes. Rider style is a preference.

If you'd personally like to bomb a downhill run as fast as you can with 140mm rotors front and rear than by all means go for it. After all whats the point of finding a nice downhill run just to tip toe like some granny on Sunday? However, I don't think it will work out very well for you. At least you'll PREFER the lever feel better with the small rotors (rider style).


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## bikeabuser (Aug 12, 2012)

Axe said:


> You still do not get it? Objective performance of a component has nothing to do with rider style. It performs the same independent of who rides it.


Yea, sure ... You keep telling yourself that.
I, and others have been pretty clear about this ... But your mind seems to have been made up, before you entered this thread.

Go back and read the OP's question !!



kapusta said:


> This thread is suffering badly from two distinctly different types of arguments getting confused with one another.
> 
> 1- The first set of arguments have to do with the facts. One is whether bigger rotors are more powerful. Or more specifically, do they give you more stopping force for a given amount of force on the brake lever. This is simple physics, and the answer is yes. Do they cool better? Again, physics would say yes.
> 
> ...


I'm guessing some people with preconceived notions, skim read the OP's question


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## bikeabuser (Aug 12, 2012)

Jon Richard said:


> This is a contradictory statement as modulation is synonymous with force attenuation. If less pressure is required to produce the same force then the lever will be more sensitive to inputs.


And being over-sensitive to rider input, isn't always a good thing ... YES ?


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## bikeabuser (Aug 12, 2012)

Fajita Dave said:


> That has nothing to do with rider STYLE. It has everything to do with what you NEED for the TERRAIN that your riding. If your riding downhill than you NEED stronger brakes. Rider style is a preference.
> 
> If you'd personally like to bomb a downhill run as fast as you can with 140mm rotors front and rear than by all means go for it. After all whats the point of finding a nice downhill run just to tip toe like some granny on Sunday? However, I don't think it will work out very well for you. At least you'll PREFER the lever feel better with the small rotors (rider style).


Seems like rider style/preference to me ... But go ahead and pick apart a word.


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## Axe (Jan 12, 2004)

bikeabuser said:


> Yea, sure ... You keep telling yourself that.


Apparently what I am telling _you_ is not getting through at all, so I will stop.

I have only entered this conversation to respond to a pile of utter gibberish that you so wholeheartedly agreed with. It is not about the OP question, it is about your and some others lack of understanding of some basic mechanical principles involved.


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## Jon Richard (Dec 20, 2011)

bikeabuser said:


> And being over-sensitive to rider input, isn't always a good thing ... YES ?


Yes, a slow technical rider who feels his brakes are grabby or act like an on/off switch would likely prefer smaller rotors all else being equal.

But you understand that my post was in response to an erroneous statement about rotor diameter not affecting modulation, so your quote/ respond is out of context attempting to validate a separate point.

I agree with Kapusta that two conversations are being held, one clinically and the other subjectively.


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## bikeabuser (Aug 12, 2012)

Axe said:


> *Apparently what I am telling you is not getting through at all, so I will stop.*
> 
> I have only entered this conversation to respond to a pile of utter gibberish that you so wholeheartedly agreed with. *It is not about the OP question,* it is about your and some others lack of understanding of some basic mechanical principles involved.


Disregarding the OP's question does seem to be a face saving move 

And, I guess you can also attempt to turn this into my misunderstanding of the basic question ... But your attemt is a failure, IMO.

Re-read post #1 !!!!
Bigger is NOT always better ... And as others have said ... Better is subjective.

But I'm sure you're not really done ... Are you, Mr. Hard Headed, Must Always Be Right, even when wrong, Ax'e person, you


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## bikeabuser (Aug 12, 2012)

Jon Richard said:


> Yes, a slow technical rider who feels his brakes are grabby or act like an on/off switch would likely prefer smaller rotors all else being equal.
> 
> But you understand that my post was in response to an erroneous statement about rotor diameter not affecting modulation, so your quote/ respond is out of context attempting to validate a separate point.
> 
> *I agree with Kapusta that two conversations are being held, one clinically and the other subjectively.*


So are we in agreement, or not ?


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## Jon Richard (Dec 20, 2011)

bikeabuser said:


> So are we in agreement, or not ?


What am I missing? The very first word in the first sentence of my response to your question is yes.

Is there some point of contention you're seeing in this?


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## Fajita Dave (Mar 22, 2012)

bikeabuser said:


> Seems like rider style/preference to me ... But go ahead and pick apart a word.


There is no picking apart a word when its a clear difference between necessary performance and preference. That's why they sell downhill bikes with 203mm rotors and XCs with 160mm rotors.

The OP said in the car world larger rotors don't improve stopping distance (or have more braking power). As was already explained larger rotors do have more braking power. The next part of the OPs post was if a larger rotor was worth it for the heat dissipation for *intense downhill riding.* He never mentioned if he is actually riding downhill or not so it was probably just a question he was interested in or just a way to have conversation. Since we don't know what kind of downhill riding he would be doing you can't say if 160mm would be enough or if he would need a 203mm rotor.

Depending on what kind of downhill runs hes riding and how fast he rides them he could very well *need* the largest rotors he can find. For example if hes riding in Utah with a steep 3,000ft decent at break neck speeds he will *need* large rotors for both the stronger braking performance and the heat dissipation. If however he were riding in Florida or he doesn't like to ride fast downhill than a large rotor wouldn't be necessary.

If you want to keep being political here's something to think about. Even though he'd be fine with the smallest rotors that you can fit on a mountain bike in Florida with no hills he could still *choose* to use a large rotor because it fit his riding *style* and he liked the grabby feel. On the other hand if he decided to use small rotors on a gnarly downhill that lasts a few thousand vertical feet it could very well get him *killed*. See the difference between performance and preference yet?

The point is if you want to ride a long downhill run fast you will undoubtedly need brakes to fit the terrain type. That has nothing to do with style.


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## bikeabuser (Aug 12, 2012)

If 160 is all one needs 

The Timex watch keeps ticking, regardless of the speed one attains.


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## Axe (Jan 12, 2004)

bikeabuser said:


> Disregarding the OP's question does seem to be a face saving move


No. You have ignored my point, supported an idiotic and misinformed statement and continue to spill out smug drivel. It is your face that needs saving, but I am not sure it is possible at this point.


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## Dambala (Jan 22, 2011)

Dumb question. It is simply a math equation. Larger rotor equals increased leverage.


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## Danielrg_usa (Feb 12, 2011)

Uphill=sad said:


> That's an interesting example, the Buell only had a single disc mounted on one side, I'll wager once you measure out the rotor size and divide it by two (since every every other streetbike has a twin disc setup) it'll work out very similar in leverage and surface area. My neighbor owned a Buell, I owned a Hornet, both very similar brake performance - albeit with a visually different approach.
> 
> Secondly Buell was known for edging design that stood out from the crowd, i wonder how much was based off unique looks and not a performance increase? It's a shame they are no longer available, cool bikes.


I had a 07 Buell XB9R that I loved. My ex wife had a '10 yamaha R6S. I prefered the braking of my Buell over the Yamaha. For me it was very responsive and had great feel. It also took very little effort to get the back end weightless. Just my thoughts on that.


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## ehigh (Apr 19, 2011)

Shimano made like ten sets of these ugly dual rotor brakes that even had a water reservoir under the seat for heat dissipation. They never hit the market. They just made test riders crash. 

Sent from my Desire HD using Tapatalk 2


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## solidfish (Jul 1, 2012)

Dambala said:


> Dumb question. It is simply a math equation. Larger rotor equals increased leverage.


I'm kind of lost as to where the conversations are going...


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## kapusta (Jan 17, 2004)

solidfish said:


> I'm kind of lost as to where the conversations are going...


I think at this point people are not reading the whole thread (not that I blame them), and so we are seeing a repeat of worn out points.


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## Uphill=sad (Dec 8, 2011)

kapusta said:


> I think at this point people are not reading the whole thread (not that I blame them), and so we are seeing a repeat of worn out points.


Yeah, pretty much. Was a good thread - interesting to read and I learned a few things. The answer appears to be to simple for many people to accept, even with some basics physics presented by those knowledgeable to support the answer.


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## csermonet (Feb 2, 2009)

Haven't read all these pages, but isn't this one of the most basic laws of physics in the known universe and one of the first things you learn about brakes on a bicycle? Why does everyone need graphs and maths and **** to validate it? Not really sure why people think their meaningless, uninformative "opinion" matters either. There is only room for fact here.


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## Haint (Jan 25, 2012)

Here's what I don't get: if the bike had no Rotors, it would not be able to create a line-of-leverage and act upon it for braking. 
140-160-183-203mm rotors each create a lever unique to themselves, therefore by Point A to Point B - a variable to be put to use.
If these brakings were Panic Stops, perhaps the results would be tightly clustered. But in the ups and downs of trail riding, you've got to keep on keeping on (possible future Mtbr Title...) and having a bigger brake rotor on the bike - front *or* rear - can allow more calculated braking points. 
Whether or not just swapping a rotor into a system not using it already will have the same effects as a brake setup for big rotors seems to be creating the drama in the thread.

If this thread goes on any longer, someone will have to remove their brake rotors and ride down a long trail. After, pick a brake rotor and tell us about it.


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## solidfish (Jul 1, 2012)

csermonet said:


> Haven't read all these pages, but isn't this one of the most basic laws of physics in the known universe and one of the first things you learn about brakes on a bicycle? Why does everyone need graphs and maths and **** to validate it? Not really sure why people think their meaningless, uninformative "opinion" matters either. There is only room for fact here.


I dont think its that obvious. Thats why there are major companies and organizations going out and testing the products. Although math explains the concept, it still needs to tried and tested on real world situations.


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## car bone (Apr 15, 2011)

I have a theory. Smaller discs are more powerful. they get hotter so they must somehow convert more energy from the caliper to heat when braking, they are more efficient at converting speed to heat. = more better. This sounds correct right? This can also be tested by putting a 1cm steel rod through a spinning wheel, first spin it up and put the rod out where the nipples are, then try to jam it in between the spokes of the rotor/disc and see what happens! Yup smaller = more betterer. And thats todays physikz for yall. You all get detention.


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## Saul Lumikko (Oct 23, 2012)

Good theory, but loses 6-0 to the obvious difference in leverage.

For anyone who didn't read the thread so far (and I can not blame them), here's a summary of solid facts:

1) A larger rotor has more leverage. It means it will stop the wheel from turning more effectively. This is not a matter of opinion.
2) Due to having more leverage, the modulation curve is steeper. This is also not a matter of opinion.

What _is_ a matter of opinion is whether the higher power is a good thing or not, and rider skill determines whether they can live with the increased sensitivity to lever input or not.


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## aedubber (Apr 17, 2011)

Here is some Logic , buy a few different size rotors , go ride them all, and pick the one you like best . End of story , have a nice day. Everyone will have their own " opinion " there is no right or wrong on what YOU might feel works best for YOU . Some of you actually need to get out and ride more then worry about stopping or slowing down , thats no fun anyways  .


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## bikeabuser (Aug 12, 2012)

Saul Lumikko said:


> Good theory, but loses 6-0 to the obvious difference in leverage.
> 
> For anyone who didn't read the thread so far (and I can not blame them), here's a summary of solid facts:
> 
> ...


There ya have it !!!!

This might be better performing, to some............









But that doesn't mean it's better performing, to all...................

























The last one has a low performance front brake for a reason ... And it ain't got nothing to do with rider skill, because the top guys in the MX field find the low performance sufficiently adequate


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## Saul Lumikko (Oct 23, 2012)

To clarify: the fact that sensitive brakes require more skill doesn't mean that skilled riders will always go for a larger rotor. I dare say I have the dexterity of a gynecologist, but I prefer to have a smaller rotor in the rear.

Effective stopping requires skill, no matter what brakes you use.


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## bikeabuser (Aug 12, 2012)

Saul Lumikko said:


> To clarify: the fact that sensitive brakes require more skill doesn't mean that skilled riders will always go for a larger rotor. I dare say I have the dexterity of a gynecologist, but I prefer to have a smaller rotor in the rear.
> 
> *Effective stopping requires skill, no matter what brakes you use*.


Very true, and you don't need a sledgehammer to hang a picture


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## Kronk (Jan 4, 2004)

bikeabuser said:


> Very true, and you don't need a sledgehammer to hang a picture


Hanging pictures is better with a sledgehammer. Making big holes to find the studs beats having the pictures fall off of the wall in the middle of the night, startling you from sleep just to shoot up other walls thinking it's a burglar.


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## Haint (Jan 25, 2012)

I'm waiting for someone to come back here, wanting to put their rotors back on. Hit a few trees, jumped down some ledges, just kept going faster and faster. 

They'd have some input on brakes, probably wouldn't care what size - so that might make them partial to wanting and just even having some brakes. Instead of solving the true rotor size to use for our planet.

So, if that's you - don't post just now. Wait until the thread gets back on track.


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## bikeabuser (Aug 12, 2012)

Haint said:


> I'm waiting for someone to come back here, wanting to put their rotors back on. Hit a few trees, jumped down some ledges, just kept going faster and faster.
> 
> They'd have some input on brakes, probably wouldn't care what size - so that might make them partial to wanting and just even having some brakes. Instead of solving the true rotor size to use for our planet.
> 
> So, if that's you - don't post just now. Wait until the thread gets back on track.


The thread is on track ... You're the only one suggesting riding a bike without brakes ut:


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## Haint (Jan 25, 2012)

bikeabuser said:


> The thread is on track ... You're the only one suggesting riding a bike without brakes ut:


I was merely trying to promote bike connectivity and rider participation through letting others join, and to make choices for themselves. :idea:


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## Haint (Jan 25, 2012)

solidfish said:


> It seems to be the general thought that larger rotors equals better braking. I am curious if any company or person has ever tested this on mountain bikes and provide proving data?
> 
> I ask because in performance cars, the same question is often asked.
> 
> ...


A few years ago someone in DH was testing 9-inch Rotors -- which were huge. These likely bent very easily, were out-performed by the 8" rotor.

Again, many times braking on a bike is not done to come to a complete stop. Scrub speed w/o disrupting the bikes attitude, preload before a corner, or most important - save the bike in WFO situations.

Just touching a longer-lever from a 203mm rotor in a quick dab, that will better improve braking than doing the same grab upon a 140mm rotor.


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## Guest (Mar 9, 2013)

bikeabuser said:


> Very true, and you don't need a sledgehammer to hang a picture


i beg to differ.


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## bikeabuser (Aug 12, 2012)

Haint said:


> A few years ago someone in DH was testing 9-inch Rotors -- which were huge. These likely bent very easily, were out-performed by the 8" rotor.
> 
> Again, many times braking on a bike is not done to come to a complete stop. Scrub speed w/o disrupting the bikes attitude, preload before a corner, or most important - save the bike in WFO situations.
> 
> Just touching a longer-lever from a 203mm rotor in a quick dab, that will better improve braking than doing the same grab upon a 140mm rotor.


The bigger is always better crowd, won't believe you


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## bikeabuser (Aug 12, 2012)

nvphatty said:


> i beg to differ.


LOL ... Big pictures do need big nails, and big nails often need a BFH ... Point taken !!!


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## bikeabuser (Aug 12, 2012)

Chirp Chirp, said the bigger is better crowd


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## aerius (Nov 20, 2010)

bikeabuser said:


> The last one has a low performance front brake for a reason ... And it ain't got nothing to do with rider skill, because the top guys in the MX field find the low performance sufficiently adequate


It has smaller less powerful brakes for 2 reasons:
1) It's about 1/3 to 1/2 the weight of the other bikes
2) It doesn't go nearly as fast

Same reason why a Honda Civic has low performance brakes compared to a BMW M5.


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## Saul Lumikko (Oct 23, 2012)

The people who say bigger is better are not wrong. It might really be better for them. If someone else is more comfortable with smaller rotors, they are not wrong either. It's a subjective matter! 

Larger rotors provide more braking power for any given lever input and it could be a good or bad thing. I have various rotor sizes on my bikes depending on the type of riding I do with the bike, tire size and whether it's the front or rear rotor.


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## da peach (Oct 30, 2006)

Because, aliens.


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## bikeabuser (Aug 12, 2012)

Saul Lumikko said:


> The people who say bigger is better are not wrong. It might really be better for them. If someone else is more comfortable with smaller rotors, they are not wrong either. It's a subjective matter!
> 
> Larger rotors provide more braking power for any given lever input and it could be a good or bad thing. I have various rotor sizes on my bikes depending on the type of riding I do with the bike, tire size and whether it's the front or rear rotor.


I'll never argue this ... Because it's the truth :thumbsup:


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## kayman121 (Jun 30, 2012)

It's amazing how much misinformation and subjectivity arises on an issue so easily settled objectively.

torque = moment arm crossed into force (t=r x F)

friction = coefficient of friction * normal force (no surface area dependence)

There is no "derp, screw the science jargon, what's the real world result?"

The real world stuff *is * the science. There is no mysticism to the dynamics of biking. Granted, there are more variables to consider in a real world system, but when it comes to braking, torque plays a vastly significant role, so *bigger rotor = longer moment arm = more powerful braking force per unit force applied by the pads.*


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## Saul Lumikko (Oct 23, 2012)

I sure hope that part was settled a few pages ago, but I'm scared to look.


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## kapusta (Jan 17, 2004)

kayman121 said:


> *= more powerful braking force per unit force applied by the pads.*


Yes, a couple folks in this thread got that part wrong, but it is only part of what is being discussed:

Do larger rotor sizes really improve braking? - 160 vs 180 vs 185 vs 203 etc - Page 4


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## bikeabuser (Aug 12, 2012)

Key word in the OP's title .... *Improve.*

A subjective word, for sure.

Would blue paint improve my red bike ?
Green is better ... LOL


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## Jon Richard (Dec 20, 2011)

The OP's question was asking if larger rotors increase brake performance under extreme demand citing an example with repeated high speed stops.

Stoptech's goal was to improve brake performance.

Improved brake performance in that test is defined as decreased stopping distance and reduced braking temperatures.

As rotor size increased, brake performance improved.

Bikeabuser, I like you man but you were wrong about larger rotors not offering greater stopping capacity and you are wrong about the subjectivity of "better" and "improved" as the words are used in perfect context to the original question.


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## car bone (Apr 15, 2011)

Allright I have a new theory! And this time its scientific just like in the real world media. 

Smaller rotors are more powerful because: The actual rotor spokes are shorter so the rotor is stiffer and less energy is lost as torque windup (well, less energy of the one you are supposed to lose to be able to brake at all) when braking, also since the rotor spokes are shorter the heat transfer into the hub (heatsink) from the rotor is greater thus increasing efficiency. Also since the brake track is smaller diameter you get a smaller peripheral speed for a given rpm and this saves pads. There you have it I just solved one of the biggest mysteries in the entire universe.

I also have theories about carbon vs everything, hydros vs mechs, 9 vs 10 speed. fs vs ht. 26 vs 29 and 650b etc. all highly scientific.


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## bikeabuser (Aug 12, 2012)

solidfish said:


> It seems to be the general thought that larger rotors equals better braking. I am curious if any company or person has ever tested this on mountain bikes and provide proving data?
> 
> I ask because in performance cars, the same question is often asked.
> 
> ...





Jon Richard said:


> The OP's question was asking if larger rotors increase brake performance under extreme demand citing an example with repeated high speed stops.
> 
> Stoptech's goal was to improve brake performance.
> 
> ...


I guess we should just agree to disgaree


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## Jon Richard (Dec 20, 2011)

I disagree with the OP's comments you highlighted in red as the test results data listed at the bottom of the link clearly shows that stopping distances and brake temps were reduced as the rotor size increased.

One can argue that the gains are negligible, but that will be the case in all pursuits of performance gains where trying to squeeze every bit of advantage will reach the point of diminishing returns, but the gains are there non the less.



Besides, this stoptech article is just one example and it was cited partly in an effort to ask if anyone had conducted such a test with MTB brakes. 

You won't find a test that shows smaller rotors increasing braking capacity even minutely, this is testable, demonstrable, and repeatable and has been done so ad nauseum.

I would love to see you try to argue this with the engineers and racers over at corner carvers.


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## solidfish (Jul 1, 2012)

^ Based on Stoptech's data, in normal braking conditions, the braking distance between smaller and larger rotors were 1% or less, so I said it was almost negligible.

But under intensive braking, where the brake pads were starting to fade due to high heat, there was more noticeable differences. Here, the larger rotors were able to dissipate the heat more effectively and therefore kept the stopping distances shorter than the smaller rotors.

But the key point was that the larger rotors gave noticeable benefits in high temperatures. So my original question was do mountain bike brakes also reach high temps where more heat dissipation is necessary? I think the answer is no, as no one here really experience brake fade.

Therefore, one could conclude that under normal braking conditions, larger rotors are not necessary as they do not reduce the braking distance significantly.

*However*, the larger rotors do provide less leverage force, which was shown through the equations and testimonies. But that wasnt really part of the original question.


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## solidfish (Jul 1, 2012)

^ I should clarify that when I now say "noticeable", I dont mean to contradict my original statement of "nearly negligible". Jon Richards is right, Stoptech shows that there were reduce distances. But if you calculate the percentage gains, it was under 1% for normal braking and like 2% for intense braking. 

2% is a good gain, but that's under intense braking. So my original question was - how often do we intense brake, to the point where the pads start to fade? Because its in those situations where the larger rotor's 2% gain would be beneficial.


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## bikeabuser (Aug 12, 2012)

^^^ Someone will soon correct your thoughts and intentions


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## solidfish (Jul 1, 2012)

Here is how I got those percentage numbers based on Stoptech's data. For sake of readability, I'm only showing the smallest, middle and largest rotors.


*Distances in feet*
RotorSize: 296mm 324mm 355mmm %change 
@NormalSpeed 118ft 117ft 115ft 0.8%, 2.0%
@HighSpeed 333ft 328ft 326ft 1.5%, 2.1%

Based on those percentages, I stated the benefits as being nearly negligible.


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## solidfish (Jul 1, 2012)

And for those who may be wondering - so why does Stoptech want us to buy their bigger rotor kits?

Answer = temperature. Larger rotors has much lesser surface temperature thereby reducing the possibility of brake fade.

Again from their charts:


*Temperatures in Farhenheit*
RotorSize: 296mm 324mm 355mmm %change
@NormalSpeed 706F 553F 438F 21.6%, 38%
@HighSpeed 804F 721F 594F 10.3%, 26.1%

So this is why I asked if any riders out there were having brake fade issues. Because if they are, the larger rotors can help reduce it *significantly*.


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## jeffscott (May 10, 2006)

solidfish said:


> Here is how I got those percentage numbers based on Stoptech's data. For sake of readability, I'm only showing the smallest, middle and largest rotors.
> 
> 
> *Distances in feet*
> ...


What appears to be missing from this data is brake fade....Brake fade occurs at high pad and rotor temperatures....

So assuming of course that the same mass and velocity are stopped....that has the number of stops and the energy put into the brake increases the smaller rotors will run hotter and reach a critical temperature at which brake fase occurs....then the small rotor stopping distance will increase dramatically.....the larger rotor will hang on for a few more stops the also be subjected to braked fade...

On my MTB bike with 160mm rotors brake and organic pads brake fad is noticable after about 10 minutes of high speed decending.

With 203 rotors and sintered pads I have yet to encounter brake fad and have decending for over 20 minutes.


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## Saul Lumikko (Oct 23, 2012)

You are ignoring a very important thing when looking at the Stoptech article and data: even the smaller rotors are capable of producing lockup on the wheels, if the brake is set up like that. They are using different size caliper pistons to increase or decrease pad compression as necessary to avoid this kind of excessive power.

Of course lockup is too much, and the most effective braking is right at the point before the wheel locks up. What they are doing is balancing the front and rear to get both ends to brake almost at lockup. We do the same thing on bikes by modulating the left and right lever with our fingers. You also see smaller rotors in the rear for the very same reason: braking power balance.

So if a smaller disc is capable of producing lockup of the wheel, a larger rotor will not stop the bike faster, because stopping the _wheel_ and stopping the _bike_ are two different things. Traction is the limiting factor there, and playing with disc sizes doesn't give you more traction. However, a larger rotor will give you the "almost lockup" power with less force on the lever. Whether this is a good thing or not is up to the rider.


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## solidfish (Jul 1, 2012)

jeffscott said:


> What appears to be missing from this data is brake fade....Brake fade occurs at high pad and rotor temperatures....


Sorry Jeff I updated the table. It should have said "@NormalSpeed", not "@NormalTemp". Stoptech ran their tests at 60mph and 100mph to see how they work under highway conditions and track racing conditions.

I believe they did have fade near the end of their test runs. I dont know if those distances were calculated into their averages.


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## solidfish (Jul 1, 2012)

Saul Lumikko said:


> However, a larger rotor will give you the "almost lockup" power with less force on the lever. Whether this is a good thing or not is up to the rider.


You are correct about the lockups on bikes but this isn't a factor in this case. The 350z comes with ABS. For Stoptech's tests, I believe they just slammed on the brakes right up until the point of ABS initiating.

And yes they had larger calipers for the larger rotors but that still didnt reduce the braking distance significantly, as shown on the tables above.


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## bikeabuser (Aug 12, 2012)

solidfish said:


> And for those who may be wondering - so why does Stoptech want us to buy their bigger rotor kits?
> 
> Answer = temperature. Larger rotors has much lesser surface temperature thereby reducing the possibility of brake fade.
> 
> ...


And in a *multi-mile race*, where hard braking is the norm ... Brake fade does become an issue.


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## bikeabuser (Aug 12, 2012)

Saul Lumikko said:


> You are ignoring a very important thing when looking at the Stoptech article and data: even the smaller rotors are capable of producing lockup on the wheels, if the brake is set up like that. They are using different size caliper pistons to increase or decrease pad compression as necessary to avoid this kind of excessive power.
> 
> Of course lockup is too much, and the most effective braking is right at the point before the wheel locks up. What they are doing is balancing the front and rear to get both ends to brake almost at lockup. We do the same thing on bikes by modulating the left and right lever with our fingers. You also see smaller rotors in the rear for the very same reason: braking power balance.
> 
> So if a smaller disc is capable of producing lockup of the wheel, a larger rotor will not stop the bike faster, because stopping the _wheel_ and stopping the _bike_ are two different things. Traction is the limiting factor there, and playing with disc sizes doesn't give you more traction. However, a larger rotor will give you the "almost lockup" power with less force on the lever. Whether this is a good thing or not is up to the rider.


Obviously, you understand the situation :thumbsup:

The exception being the overall design of the system ... It is possibly to create a brake system that requires great effort to engage, and another system that if breathed upon goes into almost instantaneous lock-up ... Neither is good for the average rider, and either can be accomplished with a given lever force.

That's why brakes really should be looked at as a system ... Changing one component ONLY (rotor size) will typically result in worse performance than a designed system ... And that's why I've been saying all along that a bigger rotor isn't always better.

I guarantee you I can make a 203mm rotor suck


----------



## Jon Richard (Dec 20, 2011)

bikeabuser said:


> Obviously, you understand the situation :thumbsup:
> 
> The exception being the overall design of the system ... It is possibly to create a brake system that requires great effort to engage, and another system that if breathed upon goes into almost instantaneous lock-up ... Neither is good for the average rider, and either can be accomplished with a given lever force.
> 
> ...


I agree, but larger rotors will always have greater mechanical advantage and thermal capacity. So when putting together a brake system intended for hard braking in a multi-mile race larger rotors will be more suitable for the task.

Larger rotors aren't always "better", but will always offer greater braking capacity.

This whole discussion is really making me wish I had brought my temp gun with me when I went on a lift assisted ride. We don't hit the speeds of autos nor carry the same weight, but on the other hand these systems are tiny in comparison and the rotors aren't vented with the exception of the Hopes.

This is really an apples to oranges comparison as the brake systems between a 350z and our bikes are much different. I think the fact that we run manual brakes plays a role in what size rotors one would choose for their bike as braking effort on a car with vacuum assist isn't much of a consideration. If someone is experiencing brake fade or excessive braking effort larger rotors are a sensible consideration.


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## bikeabuser (Aug 12, 2012)

Jon Richard said:


> I agree, but larger rotors will always have greater mechanical advantage and thermal capacity. So when putting together a brake system intended for hard braking in a multi-mile race larger rotors will be more suitable for the task.
> 
> Larger rotors aren't always "better", but will always offer greater braking capacity.
> 
> ...


Within a designed system I would agree ... But within an aborted DIY situation ... Meh, almost don't want to go there.

And that's exactly why I can say bigger isn't always better ... An aborted system is hit or miss, and because of this, bigger doesn't automatically equal better ... Even if some want that to be true.


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## Jon Richard (Dec 20, 2011)

bikeabuser said:


> Within a designed system I would agree ... But within an aborted DIY situation ... Meh, almost don't want to go there.
> 
> And that's exactly why I can say bigger isn't always better ... An aborted system is hit or miss, and because of this, bigger doesn't automatically equal better ... Even if some want that to be true.


I guess I would need an example of an "aborted system" to better understand the point you're conveying. Are you talking about mixing and matching levers and calipers not sold as a set or something?

Bigger always automatically means greater thermal capacity and mechanical advantage.


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## 1niceride (Jan 30, 2004)

When designing a brake system leverage ratio between the lever and pads also plays a factor in all this. With larger or 2 rotors one can back off on the leverage ratio to maintain same braking force. Inexpensive autos use the smallest rotor with the most leverage ratio needed to get the job done. Larger leverage ratios require more travel at the pedal or lever to actuate the pads. Softer pedal or lever will result cause of the increased line pressure. 

Using larger rotors one can cut back on the pedal or lever to pad ratio and get a better feel and road feedback. Also the pedal or lever will pick up the rotor faster off the top. 

It is an application/site specific area where it should be designed as a whole system together. Though with a bike if one could adjust lever to pad ratio with disk diameters that would be ideal...


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## Jon Richard (Dec 20, 2011)

1niceride said:


> It is an application/site specific area where it should be designed as a whole system together. Though with a bike if one could adjust lever to pad ratio with disk diameters that would be ideal...


I don't think that will ever happen in the world of MTB's. I can buy Wildwood, Brembo, Bear etc.. in whatever cylinder diameters I want but somehow there is too much liability involved in allowing me to tune my own bicycle.


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## 1niceride (Jan 30, 2004)

Jon Richard said:


> I don't think that will ever happen in the world of MTB's. I can buy Wildwood, Brembo, Bear etc.. in whatever cylinder diameters I want but somehow there is too much liability involved in allowing me to tune my own bicycle.


Not sure how to say this...bicycles are for children also. Autos are primarily for adults who might exercise some caution or have some mechanical skills. Like yourself. But as noticed here at mtbr I can see some issues with too much adjustablity with the adults also...

The leverage ratio adjustment could be done in the lever without changing calipers.


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## Jon Richard (Dec 20, 2011)

1niceride said:


> Not sure how to say this...bicycles are for children also. Autos are primarily for adults who might exercise some caution or have some mechanical skills. Like yourself. But as noticed here at mtbr I can see some issues with too much adjustablity with the adults also...


Still, limited to upper end parts as in the world of autos I think it would be nice.

As it stands changing rotor diameters and pad compounds are the limit, unless you want to prototype and machine your own wares.


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## 1niceride (Jan 30, 2004)

Jon Richard said:


> Still, limited to upper end parts as in the world of autos I think it would be nice.
> 
> As it stands changing rotor diameters and pad compounds are the limit, unless you want to prototype and machine your own wares.


Several years ago some one grafted Magura Julie calps(larger piston) with shimano levers...said it worked acceptably..Go opposite to decrease ratio obviously.


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## One Pivot (Nov 20, 2009)

bikeabuser said:


> That's why brakes really should be looked at as a system ... Changing one component ONLY (rotor size) will typically result in worse performance than a designed system ... And that's why I've been saying all along that a bigger rotor isn't always better.


... you're not aware that most brakes from the manufacturer come in different rotor sizes? This is baffling. They ONLY change the rotor size in their "designed systems".

So in short, what you've been saying all along has been based off something completely untrue. Its time to throw in the towel on this one :lol:

Cars are a completely different system in every way. The big brake argument for cars has absolutely tons to do with the ratios of the hydraulic system and proportioning. You have a lot of fixed variables in a car that bikes do not have. We have 2 brake levers on a bike operating 2 discs, you've got one on a car and it operates 4 discs, plus a proportioning valve. Totally different, very irrelevant. You dont fall over your steering wheel when you press your car brakes too hard either, and you cant drag a rear brake on a car.

For safety, a lot of cars have forward brake bias so the rear doesnt spin out. Installing larger front brakes/rotors makes the bias worse, and performance can decrease. Larger rear brakes or changing the proportioning valve can improve stopping performance. Removing front weight and putting it in the rear helps drastically as well, if the brakes can be setup to follow the weight.

Theres lots to car braking systems, it just doesnt really cross over to brakes. Having really grabby car brakes isnt too bad at all, many people like it. Really grabby bike brakes make you crash.


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## 1niceride (Jan 30, 2004)

One Pivot said:


> ... you're not aware that most brakes from the manufacturer come in different rotor sizes? This is baffling. They ONLY change the rotor size in their "designed systems".
> 
> So in short, what you've been saying all along has been based off something completely untrue. Its time to throw in the towel on this one :lol:
> 
> ...


You should be happy with current design then...all is well.

I do know that many with bb7's coupled with adjustable leverage ratio levers like to dial rotor size and leverage ratio to get that feel they like. I'm not sure how many otb's thats caused.

That lack of bias in the rear is a pita on the wifes fwd car. I'm constantly using the hand brake to spin the rear around in the winter. Some of my auto friends adjust that porp valve to their liking. Being able to tweak-priceless.


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## Jon Richard (Dec 20, 2011)

One Pivot said:


> Cars are a completely different system in every way. The big brake argument for cars has absolutely tons to do with the ratios of the hydraulic system and proportioning. You have a lot of fixed variables in a car that bikes do not have. We have 2 brake levers on a bike operating 2 discs, you've got one on a car and it operates 4 discs, plus a proportioning valve. Totally different, very irrelevant.


Absolutely. There is no need to factor in the leverage ratios of rotors in a brake system having the front and rear independently operated, that is a function of tuning the brake bias.

Some automotive systems do run independent master cylinders for front and rear, but are still operated by one pedal where brake bias must be adjusted through master/slave cylinder diameter selection and dialed in with either a balance bar at the pedal arm, proportioning valve, or both like this system I put together for an old Ford Falcon of mine-









Here's a shot of the pedal assembly with the balance bar I made-









Bikes are so radical, simple with no valving to figure out. Hell we don't even have to work with DOT fluid anymore.


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## kapusta (Jan 17, 2004)

bikeabuser said:


> ... Changing one component ONLY (rotor size) will typically result in worse performance than a designed system ...


This is complete nonsense. Many brakes are offered in different rotor sizes, the ONLY difference being the rotor and the adapter for mounting the caliper.

Further, if you ever actually TRIED this, you would know this claim is complete nonsense.


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## bikeabuser (Aug 12, 2012)

Jon Richard said:


> I guess I would need an example of an "*aborted system*" to better understand the point you're conveying. Are you talking about *mixing and matching levers and calipers not sold as a set *or something?
> 
> Bigger always automatically means greater thermal capacity and mechanical advantage.


Absolutely ... Because the factor being changed within this discussion, is rotor size ... You're not exchanging complete systems.

If we want to go there ... Then a lot of rewrite needs to occur by many, because now we'd be discussing,
Company A's Brake System
vs
Company A's OTHER Brake System
vs
Company B's Brake System
vs
Company C's Brake System

Rinse, Lather, Repeat


----------



## bikeabuser (Aug 12, 2012)

Jon Richard said:


> I don't think that will ever happen in the world of MTB's. I can buy Wildwood, Brembo, Bear etc.. in whatever cylinder diameters I want but somehow *there is too much liability involved in allowing me to tune my own bicycle.*


I hope this idea never catches on, Jon


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## bikeabuser (Aug 12, 2012)

One Pivot said:


> ... you're not aware that most brakes from the manufacturer come in different rotor sizes? This is baffling. They ONLY change the rotor size in their "designed systems".
> 
> So in short, what you've been saying all along has been based off something completely untrue. Its time to throw in the towel on this one :lol:
> 
> ...


With all due repsect, you are limiting your abilities, if you stay inside the box.


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## bikeabuser (Aug 12, 2012)

1niceride said:


> You should be happy with current design then...all is well.
> 
> I do know that many with bb7's coupled with *adjustable leverage ratio levers* like to dial rotor size and leverage ratio to get that feel they like. I'm not sure how many otb's thats caused.
> 
> That lack of bias in the rear is a pita on the wifes fwd car. I'm constantly using the hand brake to spin the rear around in the winter. Some of my auto friends adjust that porp valve to their liking. Being able to tweak-priceless.


That's more than enough for me to say with confidence that I can make a 203mm rotor SUCK


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## kapusta (Jan 17, 2004)

bikeabuser said:


> Absolutely ... Because the factor being changed within this discussion, is rotor size ... You're not exchanging complete systems.
> 
> If we want to go there ... Then a lot of rewrite needs to occur by many, because now we'd be discussing,
> Company A's Brake System
> ...


 YOU are the only one mentioning comparing one complete brake system to another. Nobody else sees this as remotely relevant because, in fact, it is not.


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## bikeabuser (Aug 12, 2012)

kapusta said:


> This is complete nonsense. Many brakes are offered in different rotor sizes, the ONLY difference being the rotor and the adapter for mounting the caliper.
> 
> Further, if you ever actually TRIED this, you would know this claim is complete nonsense.


Tell me something NEW, and you might have a point.


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## bikeabuser (Aug 12, 2012)

kapusta said:


> YOU are the only one mentioning comparing one complete brake system to another. Nobody else sees this as remotely relevant because, in fact, it is not.


Really ?
Then why have the word's _caliper_ and _lever_ now entered the discussion ?

We've been talking about changing rotor size, and without making other changes to the braking system (my position all along), it's gonna be hit or mis as to how much, if any performance gain is acheived.

It's no different than putting a racing cam in an engine ... If you don't make other changes, you're not gonna get what you're looking for.


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## kapusta (Jan 17, 2004)

bikeabuser said:


> Tell me something NEW, and you might have a point.


So, you were already aware that your point about changing rotor size screwing up a "deigned system" is complete nonsense?


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## kapusta (Jan 17, 2004)

bikeabuser said:


> Really ?
> Then why have the word's _caliper_ and _lever_ now entered the discussion ?


Your just trolling now.


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## ehigh (Apr 19, 2011)

kapusta said:


> Your just trolling now.


Don't feed em. They're kinda a time burner and life waster.

Sent from my Desire HD using Tapatalk 2


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## bikeabuser (Aug 12, 2012)

kapusta said:


> So, you were already aware that your point about changing rotor size screwing up a "deigned system" is complete nonsense?


Sure it is ... You keep telling yourself that the rotor, caliper, and lever + it's adjustability are not a designed system, and I'll keep telling you that you are wrong.


kapusta said:


> You're just trolling now.


Yea, I got that from your negative REP LOL

Just admit it ... These are designed systems.
Call any manufacturer of these components and ask them if brand X component will work with brand Y component, and ask for a guarantee that it will work... They won't tell you it will work for one simple reason, it's not part of their design.


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## kapusta (Jan 17, 2004)

bikeabuser said:


> Call any manufacturer of these components and ask them if brand X component will work with brand Y component, and ask for a guarantee that it will work... They won't tell you it will work for one simple reason, it's not part of their design.


This is irrelevant.


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## kapusta (Jan 17, 2004)

*Yes, I neg rep'ed you...*

@Bikeabuser: Yes, I neg rep'ed you. Why? Because you are being a troll, and that is the one thing I neg rep for. I don't do it often maybe once or twice a year.

You have knowingly made several claims that are demonstrably untrue, and it wastes peoples' time correcting this. More importantly, however, other peoples' attempts to correct this misinformation just results in you dragging in irrelevant lines of argument in an attempt to further confuse things. When all this is done _intentionally_, that is trolling, and it takes away from the value of what can be a useful place to get good info.

Anyway, congrats on getting me to waste time and energy feeding you for so much of this thread.


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## Jon Richard (Dec 20, 2011)

bikeabuser said:


> We've been talking about changing rotor size, and without making other changes to the braking system (my position all along), it's gonna be hit or mis as to how much, if any performance gain is acheived.


You keep throwing in new variables to deflect and steer the discussion away from your erroneous assertions.

Larger rotors will always have greater thermal capacity and mechanical advantage, you may have a unique talent for making a 203 rotor "suck", but no matter now hard you try you will never make a larger rotor have less thermal capacity and mechanical advantage than a smaller one. So although these properties don't translate into better for all situations it does mean the potential for greater braking capacity will always be higher with larger rotors.

Your post about an aborted system in no way related to my comment about larger rotors being a sensible consideration to mitigate brake fade and arm pump.


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## kapusta (Jan 17, 2004)

Jon Richard said:


> You keep throwing in new variables to deflect and steer the discussion away from your erroneous assertions.


Yes, that is classic trolling.

You can't "win" against a troll.


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## Mr.P (Feb 8, 2005)

If bigger rotors do not have more thermal capacity, and do not have more leverage, and do not improve stopping, then you should be able to go the other direction.

140mm rotors on a DH sled. 

I can see them on the three titanium rotor bolt, world cup DH weight weenie racers bikes this season. lol.

P


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## Saul Lumikko (Oct 23, 2012)

solidfish said:


> You are correct about the lockups on bikes but this isn't a factor in this case. The 350z comes with ABS. For Stoptech's tests, I believe they just slammed on the brakes right up until the point of ABS initiating.
> 
> And yes they had larger calipers for the larger rotors but that still didnt reduce the braking distance significantly, as shown on the tables above.


Precisely: even the smaller rotors were capable of lockup, so braking distance was primarily limited by ABS and traction, not disc size. Anyone surprised that a larger rotor made little difference? Not me.

A larger rotor is more effective at stopping the wheel, but if you run out of traction (ABS activates, if present), rotor size really isn't a factor anymore. It's "large enough". At that point the advantage is reduced brake fade - also well documented and not the least bit surprising.

What a larger rotor does do is allow you to get the same braking power for less lever input.

As for whole systems screwing up by changing variables, I don't think it's as simple as that. For example I bought two sets of Avid BB7's with 185 mm rotors. I found the rear brake to be difficult to modulate on my 29er: just a slight pull with one finger would easily lock the rear wheel even with my weight back. I changed to a 160 mm rotor and got far better modulation. Another example: I took the discarded 185 mm rotor and put it on my Prophet, which originally had 160 mm rotors front and rear. Naturally in the front. While the original brake setup wasn't bad (26" tires have less leverage than 29ers so you can get away with a smaller rotor) I liked the new sharper response of the brake.

You just need to know what you're doing.


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## Jon Richard (Dec 20, 2011)

Larger rotors have greater thermal capacity and mechanical leverage, but it is the greater thermal capacity that gives them greater braking capacity as the function of brakes is in essence to convert kinetic energy into thermal energy. 

The mechanical advantage part of that equation can be achieved with different piston diameters, but with two identical systems save for rotor size if traction isn't a limiting factor the one with larger rotors would exhibit a shorter stopping distance. However if the ratios were adjusted so as to deliver equal force the mechanical advantage would become moot, yet the one with larger rotors would still out perform the other under repeated or extreme brake applications on account of better heat management.

As far as the 350z's the caliper swapping was for reasons explained in the first paragraph under the first chart for the Audi S4.


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## Saul Lumikko (Oct 23, 2012)

I beg to argue that the mechanical advantage directly causes them to stop the wheel more effectively without consideration to thermal capacity. 

Think about this example: a very very small rotor on one wheel and a huge rotor on another. Both wheels are still, and both brake systems are otherwise identical. The levers are pulled with equal force, so resting friction between the pads and rotor is the same for both systems. Then an attempt is made to make the wheels turn: the system with the smaller rotor will give up and start moving sooner because of mechanical leverage. 

For this reason my position is that larger rotors are more effective at stopping the wheel. Also the reduced heat buildup is not only due to more material and dissipation, but less heat is generated in the first place.

Larger piston diameters is different: it increases braking power by increasing friction between the pads and rotor, which causes the pads and rotor to get hot more quickly. Kinda like pulling harder on the levers.


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## 1niceride (Jan 30, 2004)

The initial post was do larger rotor sizes really improve braking?. 

The second post should have been in what way would you like to improve braking...

Sure, duty cycle factors in to it...

It just would be nice to be able to make small adjustments to lever ratio, kinda like shimano servowave thingy, like on my slx levers but with a manual adjustment knob to fine tune total lever leverage ratio. Some here seem weak in hand and want easier lever pull.

And another thought..Total braking system is in the eyes of the beholder.
A left wing brake designer will not have the same set up as a right wing brake designer. 

and thats the truth..ppppfffttt (ruth buzzy imitation).


----------



## Jon Richard (Dec 20, 2011)

Saul Lumikko said:


> Think about this example: a very very small rotor on one wheel and a huge rotor on another. Both wheels are still, and both brake systems are otherwise identical. The levers are pulled with equal force, so resting friction between the pads and rotor is the same for both systems. Then an attempt is made to make the wheels turn: the system with the smaller rotor will give up and start moving sooner because of mechanical leverage.


I agree:



Jon Richard said:


> &#8230;with two identical systems save for rotor size if traction isn't a limiting factor the one with larger rotors would exhibit a shorter stopping distance.





Saul Lumikko said:


> I beg to argue that the mechanical advantage directly causes them to stop the wheel more effectively without consideration to thermal capacity.


I would agree that the mechanical advantage offered by larger rotors stop a wheel more *efficiently*, but contend that the increased braking capacity is attributed to thermodynamics.

Even though changing piston diameters is different in terms of how it increases braking power it is still just another form of mechanical advantage and the same holding force of the wheel can be produced . In your example above the wheel with the really small rotor would hold as long as the one with the huge rotor if the caliper piston area was increased proportionately. Both approaches are equally effective, but the system with a larger rotor requires less work to produce an equal effect and therefore is certainly more efficient.



Saul Lumikko said:


> Larger piston diameters is different: it increases braking power by increasing friction between the pads and rotor, which causes the pads and rotor to get hot more quickly. Kinda like pulling harder on the levers.





Saul Lumikko said:


> Also the reduced heat buildup is not only due to more material and dissipation, but less heat is generated in the first place.


These points are why I hold that larger rotors having more potential for greater braking capacity is solely attributed to heat management. Two wheels with brakes having identical holding power but accomplished with different rotor and piston sizes will exhibit the same stopping distance, but the one with the smaller rotor will fade first under severe repeated braking.


----------



## solidfish (Jul 1, 2012)

Jon Richard said:


> The mechanical advantage part of that equation can be achieved with different piston diameters, but with two identical systems save for rotor size if traction isn't a limiting factor the one with larger rotors would exhibit a shorter stopping distance





Jon Richard said:


> These points are why I hold that larger rotors having more potential for greater braking capacity is solely attributed to heat management. Two wheels with brakes having identical holding power but accomplished with different rotor and piston sizes will exhibit the same stopping distance, but the one with the smaller rotor will fade first under severe repeated braking.


I believe your first post quoted above was mis-typed, or I mis-read, as your second post seems to contradict it. The stoptech data shows that larger rotors gave nearly insignificant gains in reducing stopping distance. It was less than 2% on their smallest vs largest comparisons. The advantages of larger rotors were their lower surface temperatures (over 35% cooler on the larger rotors).


----------



## Jon Richard (Dec 20, 2011)

Jon Richard said:


> The mechanical advantage part of that equation can be achieved with different piston diameters, but with two identical systems save for rotor size *if traction isn't a limiting factor* the one with larger rotors would exhibit a shorter stopping distance.





solidfish said:


> I believe your first post quoted above was mis-typed, or I mis-read, as your second post seems to contradict it. The stoptech data shows that larger rotors gave nearly insignificant gains in reducing stopping distance. It was less than 2% on their smallest vs largest comparisons. The advantages of larger rotors were their lower surface temperatures (over 35% cooler on the larger rotors).


The tests performed by Stoptech were limited by traction, the last run with their big brake kit had bigger tires and exhibited nearly a 20ft shorter stopping distance.


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## clunkklonk (Jan 26, 2013)

Saul Lumikko said:


> For this reason my position is that larger rotors are more effective at stopping the wheel. Also the reduced heat buildup is not only due to more material and dissipation, but less heat is generated in the first place.


This made my brain twist and warp.

Are we not transforming the same amount of kinetic energy to thermal energy, regardless of rotor size?


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## RadBartTaylor (Dec 1, 2004)

Lest we forget that with a change in piston size to increase power is only feasible up to a point since on bikes there are size limitations, clearance limitations and weight limitations. I'd guess that the systems that are currently on the market are an 'optimized' blend of these parameters. The only real option is rotor size.

Cars/Motorcycles have very tight tolerances, much more so than a bike.

With an increase in braking force comes a decrease in piston travel, hence lower disc clearance, am I on the right track with that? I can't imagine the hassle that would bring since rotors don't stay true for long.


----------



## clunkklonk (Jan 26, 2013)

ArizRider said:


> Lest we forget that with a change in piston size to increase power is only feasible up to a point since on bikes there are size limitations, clearance limitations and weight limitations. I'd guess that the systems that are currently on the market are an 'optimized' blend of these parameters. The only real option is rotor size.
> 
> Cars/Motorcycles have very tight tolerances, much more so than a bike.
> 
> With an increase in braking force comes a decrease in piston travel, hence lower disc clearance, am I on the right track with that? I can't imagine the hassle that would bring since rotors don't stay true for long.


I believe that some brakes have non linear leverage ratios. Less problems with disc clearance with larger pistons. I do not know how it's done, but it sounds like a good idea.


----------



## Jon Richard (Dec 20, 2011)

clunkklonk said:


> This made my brain twist and warp.
> 
> Are we not transforming the same amount of kinetic energy to thermal energy, regardless of rotor size?


The greater mechanical advantage of larger rotors will require less caliper force and therefore less friction and heat generated.



ArizRider said:


> Lest we forget that with a change in piston size to increase power is only feasible up to a point since on bikes there are size limitations, clearance limitations and weight limitations. I'd guess that the systems that are currently on the market are an 'optimized' blend of these parameters. The only real option is rotor size.
> 
> Cars/Motorcycles have very tight tolerances, much more so than a bike.
> 
> With an increase in braking force comes a decrease in piston travel, hence lower disc clearance, am I on the right track with that? I can't imagine the hassle that would bring since rotors don't stay true for long.


This is spot on. Many of my comments are hypothetical for the sake of the discussion.


----------



## 1niceride (Jan 30, 2004)

ArizRider said:


> Lest we forget that with a change in piston size to increase power is only feasible up to a point since on bikes there are size limitations, clearance limitations and weight limitations. I'd guess that the systems that are currently on the market are an 'optimized' blend of these parameters. The only real option is rotor size.
> 
> Cars/Motorcycles have very tight tolerances, much more so than a bike.
> 
> With an increase in braking force comes a decrease in piston travel, hence lower disc clearance, am I on the right track with that? I can't imagine the hassle that would bring since rotors don't stay true for long.


Most bike calipers are seal return style. The piston seal retracts the piston. They are not "sucked" back by the master.


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## clunkklonk (Jan 26, 2013)

Jon Richard said:


> The greater mechanical advantage of larger rotors will require less caliper force and therefore less friction and heat generated.


Still twisting my brain... 

The energy has to go somewhere. The first law of thermodynamics, conservation of energy and so on...

The larger rotor is travelling at a higher speed, thus taking the same amount of energy at lower caliper force.


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## 1niceride (Jan 30, 2004)

and another thing..large master coupled with large slave or caliper has lower line pressure compared to small master/small caliper with same leverage ratio,ie less hose expansion gives firmer feel at the lever with more road feedback. 

To the original post, I think improvement in braking by easier lever pull is all he or she was looking for.

The work=force x distance thingy applies to braking systems. Smaller rotor (less distance ie slower rotor speed) with more caliper force = larger rotor(more distance ie faster rotor speed) with lower caliper force. The truth is in the math...


----------



## solidfish (Jul 1, 2012)

Jon Richard said:


> The tests performed by Stoptech were limited by traction, the last run with their big brake kit had bigger tires and exhibited nearly a 20ft shorter stopping distance.


Dont mean to argue but their best run was only 6ft difference between the smallest and largest rotors. (not sure where you read 20ft). And thats at 100mph which requires over 329ft skid pad, making the total difference less than 2%. And that was with the better tires, lighter wheels, larger calipers and more pistons! So really, the rotor size did not reduce the braking distance significantly.


----------



## Jon Richard (Dec 20, 2011)

clunkklonk said:


> Still twisting my brain...
> 
> The energy has to go somewhere. The first law of thermodynamics, conservation of energy and so on...
> 
> The larger rotor is travelling at a higher speed, thus taking the same amount of energy at lower caliper force.


You know you're getting my brains in a knot now.

This was brought up on page three but didn't prove very fruitful. It was my understanding that the heat generated due to increased rotor velocity was not equally proportionate to leverage gain/force reduction imbued by larger rotors.

I need to calculate velocity increase vs. leverage ratio increase and take efficiency into account. I guess I'll have to crack open the books when I get home unless one better than I comes along with the solve and accompanied data which I very much hope happens as I hate homework.


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## 1niceride (Jan 30, 2004)

solidfish said:


> Dont mean to argue but their best run was only 6ft difference between the smallest and largest rotors. (not sure where you read 20ft). And thats at 100mph which requires over 329ft skid pad, making the total difference less than 2%. And that was with the better tires, lighter wheels, larger calipers and more pistons! So really, the rotor size did not reduce the braking distance significantly.


Did not read article but what was the percent difference in swept area?

The doubling of wheel resistance in braking will not result in a cutting in half the stopping distance. There are linear and non-linear relationships here that might not be intuitive just by looking..

significantly is in the eyes of the beholder...


----------



## solidfish (Jul 1, 2012)

Should note though this statement on that stoptech article:



> As we made a few more runs, the stopping distances increased as did the rear rotor temperatures. It was obvious that we had picked the wrong set of calipers for the front. Unfortunately, we were out of time, so we aborted the braking runs and moved over to the skid pad to conduct the J-Turn test.


But the overall tone of the article is that the larger brakes didnt reduce the stopping distance as much as they expected.

I pulled this article from a car racing forum and generally people are surprised when they drop thousands of dollars into a brake kit but only get 5% or less reduction in distance. As posted by Stoptech and the physics section of this thread (page 2 or so), the main benefits of larger rotors is reduction of heat, not distance.

This is why my original question was about improved braking due to heat dissipation, not distance.


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## kapusta (Jan 17, 2004)

Jon Richard said:


> The greater mechanical advantage of larger rotors will require less caliper force *and therefore less friction and heat generated*.


I would not be so sure about that. Yes, on a larger rotor you need to apply less force on the pad against the rotor. However, the rotor is moving faster past the pads, which generates more heat due to friction.

This is easily demonstrated rubbing you hands together. You can generate the same amount of heat pressing your hands together hard and moving them slowly, or rubbing very fast, while pressing more lightly.

I think the thermal advantage people speak of has more to due with what the larger rotor does with the heat that is generated.


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## Jon Richard (Dec 20, 2011)

solidfish said:


> Dont mean to argue but their best run was only 6ft difference between the smallest and largest rotors. (not sure where you read 20ft). And thats at 100mph which requires over 329ft skid pad, making the total difference less than 2%. And that was with the better tires, lighter wheels, larger calipers and more pistons! So really, the rotor size did not reduce the braking distance significantly.


I don't see you as being argumentative, I'm sorry if I'm coming off as a know it all because I certainly am not.

You are right, I misread the last paragraph believing it to be Stoptech's numbers but they were relaying what was written in sport compact car magazine so that data was not part of the control test. My apologies.


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## Jon Richard (Dec 20, 2011)

After further consideration I stand by my original statement, traction was the limiting factor in the Stoptech tests.

As Saul pointed out earlier even the smallest brakes were able to lock up and abs took over. In a test with two identical brake systems save for rotor size being insufficient to lock up the wheel the one with the larger rotor would exhibit a shorter stopping distance.


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## bikeabuser (Aug 12, 2012)

Jon Richard said:


> The tests performed by Stoptech were limited by traction, the last run with their big brake kit had bigger tires and exhibited nearly a 20ft shorter stopping distance.


Thus showing that contact patch and induced friction are related ... If a brake system can lock-up the wheel/tire combination, then the coefficient of friction comes onto play, along with tire compound and surface the tire rests upon ... YES ?


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## bikeabuser (Aug 12, 2012)

Jon Richard said:


> After further consideration I stand by my original statement, traction was the limiting factor in the Stoptech tests.
> 
> As Saul pointed out earlier even the smallest brakes were able to lock up and abs took over. In a test with two identical brake systems save for rotor size being insufficient to lock up the wheel the one with the larger rotor would exhibit a shorter stopping distance.


Thus showing that within a properly designed system, a larger rotor, IS NOT an improvement for the majority of riders.

ABS be damned, if traction is the limitation for a car, it is also a limitation for a bike ... So what good, other than thermal dissipation, is a larger rotor ... Heavier, bigger, more expensive, and most likely not needed by 99% of riders.

Is it an improvement ... Still highly subjective, as this thread indicates


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## Fajita Dave (Mar 22, 2012)

bikeabuser said:


> Thus showing that contact patch and induced friction are related ... If a brake system can lock-up the wheel/tire combination, then the coefficient of friction comes onto play, along with tire compound and surface the tire rests upon ... YES ?


If you want to be technical a larger contact patch on pavement doesn't increase traction. A larger contact patch reduces the pressure (friction) for every square inch of contact. So all you did was spread the vehicle weight over a larger contact patch. Which results in less tire wear.... but not more traction. The only ways to increase friction are with more pressure (weight or downforce) or by having a higher coefficient of friction (softer rubber / high grip pavement). Since there is less tire wear you can use a softer compound of rubber to increase grip without wearing your tires out.

For racing applications a larger tire will dissipate heat more efficiently. With how soft and tacky race tires are when hot a larger contact patch might have some gains in traction since it actually sticks to the pavement to some extent.

To stay on subject I've been thinking about going up to a 180mm rotor on my XC. I like the simplicity of mechanical brakes but I want more braking power up front. Good solution would be a larger rotor.


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## 1niceride (Jan 30, 2004)

bikeabuser said:


> Without factoring in all the other variables, stating a bigger rotor is better, is an ego inflating/deflating myth.
> 
> Surface area of pads, pad composition, rotor composition, actuation device (cable/hydraulic), mechanical advantage at lever, thermal mass of caliper, heat dissipation characteristics of various components within the system ... What else have I forgotten ?


and this thread lives on...what more is there to be said..


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## bikeabuser (Aug 12, 2012)

Fajita Dave said:


> *If you want to be technical a larger contact patch on pavement doesn't increase traction.]/b] A larger contact patch reduces the pressure (friction) for every square inch of contact. So all you did was spread the vehicle weight over a larger contact patch. Which results in less tire wear.... but not more traction. The only ways to increase friction are with more pressure (weight or downforce) or by having a higher coefficient of friction (softer rubber / high grip pavement). Since there is less tire wear you can use a softer compound of rubber to increase grip without wearing your tires out.
> 
> For racing applications a larger tire will dissipate heat more efficiently. With how soft and tacky race tires are when hot a larger contact patch might have some gains in traction since it actually sticks to the pavement to some extent.
> 
> To stay on subject I've been thinking about going up to a 180mm rotor on my XC. I like the simplicity of mechanical brakes but I want more braking power up front. Good solution would be a larger rotor.*


*

Thusly we see that coefficient of friction is a reality one must deal with 

Good solution ... Are you saying you CAN'T lock up your current brake system ?*


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## bikeabuser (Aug 12, 2012)

1niceride said:


> and this thread lives on...what more is there to be said..


Rinse, Lather, Repeat ... Until the bus wheels make a complete circle


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## Jon Richard (Dec 20, 2011)

bikeabuser said:


> ...


Yet again your quote/ respond is out of context attempting to validate a separate point.

No one is arguing that 203mm rotors are best for all bikes. If you cannot differentiate between larger rotors being better or improved (application dependant) and the fact that they have more mechanical advantage and thermal capacity (universal truth), then you cannot hope to be taken seriously when talking about designed systems when you reject the very physics that engineers must consider to design said systems.


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## 1niceride (Jan 30, 2004)

true story..

Frank the pencil pusher/keyboard guy rides Sam the mason contractor's bike and says "whats wrong with your brakes, they don't stop well". 

Sam rides Frank's bike and says "wtf is wrong with those brakes, they are real grabby". 

true story..


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## solidfish (Jul 1, 2012)

I'm confused with the conversations going on. I'm not sure what the conversations are talking about...

*To summarize this thread, I believe these were the 3 main points.*

1. Larger rotors do not decrease stopping distance significantly. That is not the ultimate purpose of larger rotors.

2. Larger rotors do dissipate heat more effectively. This is the ultimate purpose of larger rotors.

3. Larger rotors do reduce lever pressure. Thereby it makes it easier to lockup the brakes / modulate the force of your brakes.

My original questions was:
Do larger rotors really improve braking?

Answer:
If talking about distance, then no. If talking about heat dissipation or easier modulation, then yes.


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## Jon Richard (Dec 20, 2011)

You got the modulation part backwards. Brakes that are easier to lock up are harder to modulate.


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## Saul Lumikko (Oct 23, 2012)

What Jon said: with powerful brakes you have less modulation scale between "pads just touching" and "wheel locks up", so it's more difficult to get maximum braking power without losing traction. The difference between too much and too little is easily crossed. Larger rotor = more power, smaller rotor = easier to modulate.

Other than that, the summary looks good to me.

For me rotor choice was never about stopping distance or brake fade due to heat, but to me improved braking simply means a better lever feel so I can use the brakes efficiently. In some cases it has called for a larger rotor, sometimes a smaller one.


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## Fajita Dave (Mar 22, 2012)

bikeabuser said:


> Good solution ... Are you saying you CAN'T lock up your current brake system ?


Even with good sintered pads my front brake is weak with the 160mm rotor. It wont even lift the rear wheel off the ground much less lock the front tire. Its a cheap 2009 Avalanche 3.0 (first mountain bike in since I was a kid) and the stock components suck. I keep the rotor / pads clean and bed them in correctly but the mechanical brakes and 160 rotor just isn't enough and I do get brake fade depending on what trails I ride.

I thought about getting a hydro system for the front but after some more riding I thought a bigger rotor would probably be more useful to solve the brake fade and give me more braking power. I had this planned before this thread started but I wanted to see what people are saying about the SICC carbon rotors before I bought a new one .


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## Saul Lumikko (Oct 23, 2012)

Fajita Dave: Sounds like you're the perfect candidate for switching to a bigger rotor.


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## bikeabuser (Aug 12, 2012)

Saul Lumikko said:


> What Jon said: with powerful brakes you have less modulation scale between "pads just touching" and "wheel locks up", so it's more difficult to get maximum braking power without losing traction. The difference between too much and too little is easily crossed. Larger rotor = more power, smaller rotor = easier to modulate.
> 
> Other than that, the summary looks good to me.
> 
> For me rotor choice was never about stopping distance or brake fade due to heat, but to me improved braking simply means a better lever feel so I can use the brakes efficiently. *In some cases it has called for a larger rotor, sometimes a smaller one.*


And within this thread, you have people who still insist that you can't have it both ways.

Bigger is always an improvement ... Just as they have stated, all along.


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## Jon Richard (Dec 20, 2011)

bikeabuser said:


> And within this threadyou have people who still insist that you can't have it both ways.
> 
> Bigger is always an improvement ... Just as they have stated, all along.





Jon Richard said:


> No one is arguing that 203mm rotors are best for all bikes. If you cannot differentiate between larger rotors being better or improved (application dependant) and the fact that they have more mechanical advantage and thermal capacity (universal truth), then you cannot hope to be taken seriously


Stating that larger rotors offer greater braking capacity is not the same as declaring that they always improve brake performance. Unfortunately for those following the discussion this concept escapes you.


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## 1niceride (Jan 30, 2004)

Jon Richard said:


> Stating that larger rotors offer greater braking capacity is not the same as declaring that they always improve brake performance. Unfortunately for those following the discussion this concept escapes you.


I think it was written in jest...


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## bikeabuser (Aug 12, 2012)

1niceride said:


> Jon Richard said:
> 
> 
> > Stating that larger rotors offer greater braking capacity is not the same as declaring that they always improve brake performance. Unfortunately for those following the discussion this concept escapes you.
> ...


All has become such in this thread


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## Jon Richard (Dec 20, 2011)

1niceride said:


> I think it was written in jest...


It has been his hang up all along. Any mention of larger rotors increasing braking capacity elicits a retort arguing against it not improving brake performance- serious comprehension deficit where this point is concerned.



bikeabuser said:


> Thus showing that within a properly designed system, a larger rotor, IS NOT an improvement for the majority of riders.
> 
> ABS be damned, if traction is the limitation for a car, it is also a limitation for a bike ... So what good, other than thermal dissipation, is a larger rotor ... Heavier, bigger, more expensive, and most likely not needed by 99% of riders.
> 
> Is it an improvement ... Still highly subjective, as this thread indicates


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## 1niceride (Jan 30, 2004)

bikeabuser said:


> And within this thread, you have people who still insist that you can't have it both ways.
> Bigger is always an improvement ... Just as they have stated, all along.


I think this was written in jest...just a clarification.

The wife just walked by and was checking out what I was doing. She said its all in the modulation...I've known her for 35 years. She would know..


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## Jon Richard (Dec 20, 2011)

1niceride said:


> I think this was written in jest...just a clarification.


So you think he's been joking for 10 pages?


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## kapusta (Jan 17, 2004)

1niceride said:


> I think this was written in jest...just a clarification.


Joking? That's a good euphemism for it.


> The wife just walked by and was checking out what I was doing. She said its all in the modulation...I've known her for 35 years. She would know..


I thought it was all about moderation.


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## 1niceride (Jan 30, 2004)

No, not moderation...modulation. Don't let the wife know about moderation...


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## Jon Richard (Dec 20, 2011)

Well why not? If any stated fact about an increase in capacity can automatically be falsely construed as a claim that it means always better than sure, might as well loosely define thread derailing and trolling as things done in jest.


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## 1niceride (Jan 30, 2004)

Anybody who has been married for any length of time trolls each other daily. Its best just to giggle and forgetaboutit.


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## Jon Richard (Dec 20, 2011)

1niceride said:


> Anybody who has been married for any length of time trolls each other daily. Its best just to giggle and forgetaboutit.


That's sage advise, but irrelevant and in no way apropos to what was or should be being discussed.

Bigger rotors have greater braking capacity.

The original question was to broadly defined and opened the discussion to a many interesting propositions and insights, some of which were left open ended, that in my opinion was worth while to pursue as such exchanges serve to benefit the board and its members in spite of being an off shoot of the original question.

This incessant arguing of a point that no one is contesting is counter productive and absurd beyond the point of just jesting, it's abusive to the members trying to hold an intelligent exchange.

Don't be an *abuser*


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## rtsideup (Mar 21, 2012)

Was really interested in this topic.... then did the math. Reading 10 pages of blah, blah, blah.... +/- 1hr. 
1hr. of work = enough $ to buy a bigger rotor (and probably time to install it).


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## bikeabuser (Aug 12, 2012)

Jon Richard said:


> That's sage advise, but irrelevant and in no way apropos to what was or should be being discussed.
> 
> Bigger rotors have greater braking capacity.
> 
> ...


Written in a fashion that a _Registered Text Offender[/] would approve of _


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## Jon Richard (Dec 20, 2011)

bikeabuser said:


> Written in a fashion that a _Registered Text Offender[/] would approve of _


_

Your retort is not surprising at all given your propensity towards logical fallacies
Ad hominem - Wikipedia, the free encyclopedia

Here's another Proverb to go with your sig:

A prudent man deals with knowledge, but a fool exposes his folly. Prov 13:16_


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## tyrebyter (Sep 25, 2008)

The fundamental flaw is in the original question: "Do larger rotor sizes really improve braking?". It is like asking if red is a better color.


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## allthatflash (Sep 6, 2012)

Well in my expeirence, I have raced motorcycles for years and 2 things always are better#1larger rotors and better pads. most stock bikes come 305mm rotors and I switch them to 320mm narrow band rotors along with simi metallic sintered pads. This not only offers better braking with less effort it also helps in cooling the rotors faster. I think the same principle should apply to MTBs. A larger rotors will perform better and esp at higher speeds with less effort. You will save energy and won't get arm pump and once our confident on your braking you think about your run not "Oh **** am I gonna stop".Now is it worth it? that depends on you and your skill and what you want to occomplish. I have ridden 29ers and for some reason they all come with small rotors compared to my Enduro and I hate it. You have a larger then normal wheel with little rotors = bad braking. They don't offer the feel and the power I like, but to the normal Joe it will be good be enough. You make the call


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## allthatflash (Sep 6, 2012)

Saul Lumikko said:


> What Jon said: with powerful brakes you have less modulation scale between "pads just touching" and "wheel locks up", so it's more difficult to get maximum braking power without losing traction. The difference between too much and too little is easily crossed. Larger rotor = more power, smaller rotor = easier to modulate.
> 
> Other than that, the summary looks good to me.
> 
> For me rotor choice was never about stopping distance or brake fade due to heat, but to me improved braking simply means a better lever feel so I can use the brakes efficiently. In some cases it has called for a larger rotor, sometimes a smaller one.


This is some what true to a point....In Motorcycle racingThe larger brake will offer superior braking power hence you will be able to brake later and harder with less force. The stopping distance may change from corner to corner but it's all in the confidence that the brakes give it takes a motorcycle the same distance as a car to stop at full speed the larger rotors will need less force and will cool faster then smaller ones. almost 100% of all race teams will upgrade the brakes on the bike for that reason. Some of you talk about locking up the brakes...in racing thats the last thing you want to do....your smoother when you don't and the saying goes smooth is fast and fast is smooth plus it takes more energy coming into a corner skiding to slow down then someone slowing to speed then pedaling back up because he carries more momentum. Motorcycles and MTB are so much the same it's unreal


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## Saul Lumikko (Oct 23, 2012)

The notion of locking the brake is simply an example of what the brake system is capable of. If the brake system is capable of locking the brakes, your stopping distance is limited by traction and it will not become shorter even if you increase rotor size. This doesn't mean we'd actually aim to lock the brakes on purpose.

And I believe it was established earlier that racing applications require larger rotors primarily for reduced heat buildup and increased dissipation. Cooler brakes fade less.


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## EFMax (Aug 20, 2008)

Interesting to read some of the comments, I am not into physics so won’t pretend to understand everything but I do know about my bike and my riding.

I went through a quite major brake upgrade, probably to a point of over kill, but bargains were to be had at the time and the options available led me down the following path.

Me and my bike with kit, weigh in 240ibs. I enjoy some relatively technical free downhill riding in the woods and can easily reach speeds of between 35-40mph. In some sections, after a long straight, you can be face with a solid wall of trees at the T-junction ahead, so it is stop or be stopped.

Before my upgrade, and all other things being equal (weight wise and speed wise) I had a 180/160mm set of brakes with factory fitted pads. I knew exactly when I needed to brake in order to come to a complete stop and miss those trees.

Then I went to a 203/203mm set of brakes and also moved up from a basic 2pot setup to a 6pot/4pot spilt and changed the pads to ceramic compounds pads. My fav bit of downhill in my woods has three epic 600mm straights with a t-junction at the end, and the upgrade has (braking from the same point of view and pressure applied) allowed me to stop (from 40mph or 178mts per sec) to apply the brakes over 500mts later… what I take from all of this is my braking confidence has gone up because I have better margins for any errors.


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## Radical_53 (Nov 22, 2006)

The right setup doesn't change much when you start but it will make a difference at the end.
Less pressure on the lever means less fatigue in your arms. Less fatigue, on the other hand, means better modulation.
Brake pads with less or no fade are the same as better stopping power and, as there's more to gain when you pull the lever, better modulation also.
So of course large rotors won't make a difference if you just try to stop the bike once but it will make a difference on a typical ride.
The tricky question, to me, has always been the rear rotor. With an 8" rotor in the front 6" in the back always felt too weak, it had no real bite. 8" in the rear felt too grabby and had little to no modulation as the wheel locked up very easily.
7" rear rotors gave me the same lever feel as 8" in the front.

I guess it all comes down to what you're asking from your brakes. I want mine to be able to stop me in an instant, always, and want them to feel the same, all the time. This only works with large(r) rotors and pads with high(er) working temperatures (in my case sintered pads).


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## Saul Lumikko (Oct 23, 2012)

With a reasonably powerful brake system in good working order, fatigue is not an issue to me. Switching to larger rotors does make the brakes much grabbier, which means that the amount of lever input has to be controlled more accurately -> modulation is more difficult.


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## Radical_53 (Nov 22, 2006)

I guess that largely depends on how you're used to ride and where you ride.
Fading is an issue for me, easily, and so fatigue isn't far away either.
Just like everything else that reacts in a more direct, instant way better/stronger brakes have to be gotten used to. Just like a stiffer or lighter bike.


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## lew242 (Aug 7, 2008)

What's with this thread? You don't need a Phd in Physics, it's just common sense.

I have a 180mm RT76 on one bike with a SLX 666, and a the same rotor but 160mm and the same brakes on another. Simple fact is I can endo easier with less force on the larger rotor. Also modulation is pretty much the same, although that maybe a consequence of the latest generation of excellent Shimano brakes with their servo wave tech.


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## zaskar.le (Jun 20, 2011)

*Bigger discs*



Saul Lumikko said:


> With a reasonably powerful brake system in good working order, fatigue is not an issue to me. Switching to larger rotors does make the brakes much grabbier, which means that the amount of lever input has to be controlled more accurately -> modulation is more difficult.


Well coming from Motorsport type dealings the larger discs give you a larger clamping area by swept volume which equates to less pad pressures for any given braking over smaller discs the larger disc can have smaller pads/calipers for similar given braking forces as smaller discs but the point between being locked and maximum braking forces is a larger margin with bigger disc than a smaller disc.

So the smaller disc becomes more like an on off switch than a controllable medium because of the higher clamping pressure to get maximum forces to disc.

Forget ABS as that don't really stop you any quicker it just let's poor drivers keep control of the vehicle.

Maximum retardation is at the point just before you lock the wheel as once past that you speed up by law of friction.

The best braking there fore is a large disc with progressive clamping forces ie a calliper&lever that has feel to it plus someone that can control braking effort rather than using it like an on/off lever plus any heat created is dissipated over a larger area with larger disc.


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## Ridnparadise (Dec 14, 2007)

zaskar.le said:


> Well coming from Motorsport type dealings the larger discs give you a larger clamping area by swept volume which equates to less pad pressures for any given braking over smaller discs the larger disc can have smaller pads/calipers for similar given braking forces as smaller discs but the point between being locked and maximum braking forces is a larger margin with bigger disc than a smaller disc.
> 
> So the smaller disc becomes more like an on off switch than a controllable medium because of the higher clamping pressure to get maximum forces to disc.
> 
> ...


That all sounds sensible. Actually, in practical terms it is really helpful information, so thanks. Sometimes the simple stuff can be overlooked. In MTB terms does it sounds like a set of Brakeforce 1 brakes on 180mm rotors (or bigger). They have car-like modulation and a lot of force by all accounts.


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## car bone (Apr 15, 2011)

zaskar.le said:


> Well coming from Motorsport type dealings the larger discs give you a larger clamping area by swept volume which equates to less pad pressures for any given braking over smaller discs the larger disc can have smaller pads/calipers for similar given braking forces as smaller discs but the point between being locked and maximum braking forces is a larger margin with bigger disc than a smaller disc.
> 
> So the smaller disc becomes more like an on off switch than a controllable medium because of the higher clamping pressure to get maximum forces to disc.
> 
> ...


And on mtbs you can have only one side of piston(s) "active" like the bb7s, or 2 small pistons or 2 large, or 4, or 6 even. And then it would be useful to know how large the pads are. I have a feeling the more pistons the better even if the surface area of them are similar (more pad area then most likely).


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## Saul Lumikko (Oct 23, 2012)

Zaskar.le, good input and fresh point of views, thanks!

The mechanical advantage of certain levers can be adjusted, which is a bit analogous to pad size tuning: smaller rotor and higher advantage vs. larger rotor and smaller advantage would result in two systems that lock the front wheel at equal force, but the one with the larger rotor would be easier to modulate because the mechanical advantage was adjusted to compensate for the difference. Does this sound like anything like you experience with a larger rotor combined with smaller calipers / pads?


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## zaskar.le (Jun 20, 2011)

Saul Lumikko said:


> Zaskar.le, good input and fresh point of views, thanks!
> 
> The mechanical advantage of certain levers can be adjusted, which is a bit analogous to pad size tuning: smaller rotor and higher advantage vs. larger rotor and smaller advantage would result in two systems that lock the front wheel at equal force, but the one with the larger rotor would be easier to modulate because the mechanical advantage was adjusted to compensate for the difference. Does this sound like anything like you experience with a larger rotor combined with smaller calipers / pads?


hi yes thanks the principals are that you need progressive braking force and not a "grab" so you have control without snatching which is where the smaller disc loses out has the pad pressure has to be greater to equal the larger disc's force for same braking distance.

Here's one for you all to try ride along at a reasonable rate on a flat/smooth surface is best then find a line/marker first time hit the rear brake and see how long/far it takes you to stop then retry by using front brake only you will find a big difference in braking distance as the front brakes in any mode of movement do the most work and effectively there are slight changes with vehicles etc like Porsche as rear engined and front wheel drive does more on the front than rear wheel drives but on the whole it's the front that does the work.

so the best set up really is a large disc at front with a reasonable size on rear one simple way to think of it is that the front brake is before you and the rear is after you and your weight is going forwards not behind you.

One other thing you have to bear in mind is A what the forks will cope with as mine are Mazz marathon race full air with ali legs cross country type and they say 160mm max but that thing rears it's head up again yes 160 won't give you the force of a 180 plus but if i went with a 4-6 pot caliper i'd have lot's more clamping pressure!
But if i had a 203mm etc with a cable brake caliper maybe not the best one but aslong as worked that's going to be less stressfull than a hydro on a 160 that clamps like a limpet.
Because now that we have moved more to discs from rims braking the loadings/stresses have changed you now have a low down torque load on forks where as before it was spread with most around crown height.

Also on the rear there could be a limit in size by way of it ripping of ends of drop out's so something you need to find out.

When i built my car up when the first models came out had 240mm disc's that where very snatchy and very unpredictable in the wet etc with many rear ending other's then later they had 260mm which where better i used the 260mm calipers with adaptors to space them out and ran 283mm disc's and they was fantastic used mintex pads and could almost stand it on it's nose it would peel up front tyre rubber as if had window open you'd hear it tick tick as it picked up grit but it was also so controllable you could feel the edge between locked/unlocked.
One other thing was with original mintex pads was they had a groove across pads which gave you a twin leading edge.

One thing i do like with decent brakes is control for handling as if your riding switch backs in and out sort of thing say like your in a left hander and have to go right as you bring the bike up give it a dab of front brake and you will find it stands up/turns in better.

But for all it's something you have to find what works best for you and your style of riding! so try things out as ive Avid speed dials Ti which have lot's of adjustments re reach/pull leverage etc so try other things out as many different combinations ie disc/cables/levers will have various effect's.
As something that weighs 300lbs needs more braking force than something that weighs 120lbs. 
So horse's for course's as they say.


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## OneBadWagon (Mar 29, 2007)

I can't figure out if this is a serious question.


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