# How noticeable is 200-300 grams in wheels?



## D93 (Oct 19, 2011)

I currently have a set of DT Swiss M1900 and am considering switching to Stans Arch EX with Chris King or DT 240 hubs. I'm figuring the build will save about 200-300 grams, depending on the build and hub selection. I'm not sure of the exact weight of the M1900 hoops, but I'm guessing around 450 grams each, so the Arch EX will save a bit there.

Will I notice the difference on the long grinding fire road and single track climbs or during single track decents?


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## COLINx86 (Apr 8, 2009)

I guess it depends on how sensitive you are to changes on your bike. 
That said, I'm not too sensitive to changes, but I was easily able to tell a difference in 300g loss in my wheels.


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## coldryder (Aug 24, 2011)

It also depends on where the weight is lost. For example, if two wheelsets are identical but one has a hubset that is 250 grams lighter, it will likely not be noticeable. But if, for instance, the weight is lost in the rim, you'll be more likely to notice it. The further away from the hub, the more the weight loss is noticed and the more benefit is derived.

I recently purchased a set of American Classic 29 Race wheels. They are 200 grams lighter thant the American Classic 29 Tubless I was riding. I can feel the difference.


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## lightjunction (May 17, 2011)

coldryder said:


> It also depends on where the weight is lost. For example, if two wheelsets are identical but one has a hubset that is 250 grams lighter, it will likely not be noticeable. But if, for instance, the weight is lost in the rim, you'll be more likely to notice it. The further away from the hub, the more the weight loss is noticed and the more benefit is derived.


Exactly. Also, losing weight at the front of your bike is more noticeable than the back...ie: a lighter fork is more noticeable than a lighter rear wheel, even if you're losing the same amount.

As far as your weight issue goes, you may notice it, but something to consider is how much stiffness you'd be giving up (if any) for those lighter wheels. I feel like that's a more noticeable feature, at least for my type of riding.


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## 411898 (Nov 5, 2008)

Very noticable...


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## nov0798 (Nov 27, 2005)

D93 said:


> I'm not sure of the exact weight of the M1900 hoops, but I'm guessing around 450 grams each, so the Arch EX will save a bit there.


DT Swiss - M 1900


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## Jerome (Dec 21, 2003)

Rule of thumbs (summarized version) : weight in wheels = rotational weight (when your wheels are moving). Rotational weight = 3 x static weight. And the farther from the center (hub) you'll save weight, the more you'll feel it, because of the centrifugal force. So, in theory, a 300 g weight save on the rims would equate to a 900 g save on static parts like a fork, a seatpost or a frame, for example. You'll feel it for sure!


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## The Boz (Sep 28, 2011)

I would also add that you might not notice any difference on shorter rides, but you would feel fresher on longer rides with the lighter wheels, as the revolutions add up.


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## MarkMass (Sep 10, 2006)

About 8 years ago I had a set of Bontrager Mustangs w/ XT hubs on my Blur Classic. I bought a set of Mavic Crossmax (tubeless), put them on, and I could tell the difference immediately. I don't know what the weight delta was, but I was spinning up faster and riding was so much easier. It almost felt like cheating.

You can easily save 200g with lighter tires and going tubeless. It's easily the best bang for the buck in terms of performance upgrades.


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## Guest (Feb 5, 2012)

Jerome said:


> Rule of thumbs (summarized version) : weight in wheels = rotational weight (when your wheels are moving). Rotational weight = 3 x static weight. And the farther from the center (hub) you'll save weight, the more you'll feel it, because of the centrifugal force. So, in theory, a 300 g weight save on the rims would equate to a 900 g save on static parts like a fork, a seatpost or a frame, for example. You'll feel it for sure!


A grossly exaggerated rule of thumb. Rims, tires, and tubes count as 2x. Hubs are like frame weight. It is physically impossible for there to be a multiplier as high as 2x.

200g at the rim can be noticeable but not dramatic.


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## WarBoom (Dec 13, 2011)

Not sure on bikes but I know on race cars that every pound of rotational weight you remove is like removing 3lbs from the chassis. So I would say 200-300g could be like 600-900g and 1.5-2lbs would be very noticeable


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## krzysiekmz (Nov 10, 2009)

If you decide on King hubs then weight savings will not be great. Dt's on the other hand will save weight without compromising performance/durability as much. Going with Arch rims will save on rotational weight and allow for easy tubeless conversion. 

Depending on what tires you have now, you can shred 100's of grams changing tires and going tubeless. It is definetly the best way to upgrade and lighten your bike. 

Chris.


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## Guest (Feb 5, 2012)

WarBoom said:


> Not sure on bikes but I know on race cars that every pound of rotational weight you remove is like removing 3lbs from the chassis. So I would say 200-300g could be like 600-900g and 1.5-2lbs would be very noticeable


Curious why you would think a wheel on a bike would work differently than one on a car. You think the physics is different?

The translational energy of a wheel is (1/2)mv^2.

The rotational energy of a wheel is (1/2)Iω^2.

The total energy of a wheel is then 1/2(mv^2 + Iω^2).

For a wheel with all mass at the outer edge, I=mr^2, and for a rolling wheel. ω=v/r.

Substituting, we have 1/2(mv^2 + Iω^2) = 1/2((mv^2 + (mr^2)(v/2)^2) = 1/2(mv^2 + mv^2). That is precisely 2x. A real wheel will be less that 2x because its mass isn't concentrated at the outer edge. Bicycle wheels are at about 1.7x in reality when you include the hub weight.

It is physically impossible for the multiplier to be greater that 2x. Those who say differently are exaggerating what they don't understand. Race cars are 3x? No, they're not.

A difference of 200-300g of outer wheel weight will feel like 3/4-1 pound in additional inertia. Compared to the overall weight that is very small but will effect steering a little. Differences between tires will matter more.


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## Ole (Feb 22, 2004)

You might feel a difference between 300g lost at the rim and 300g lost somewhere else due to how the bike responds to your input, but the actual difference in speed is not necessarily any at all. Only in technical mountain biking do you perform enough accellerations that the diff between rotational and stationary mass makes even a theoretical difference. On road riding and xc racing, there is none.

That said, lighter wheels are less stable even if the stiffness was to be the same, but they also lets the suspension work better. So, depending on your riding style, terrain and suspension setup, lighter wheels can be either faster or slower at speed.


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## BruceBrown (Jan 16, 2004)

D93 said:


> I currently have a set of DT Swiss M1900 and am considering switching to Stans Arch EX with Chris King or DT 240 hubs. I'm figuring the build will save about 200-300 grams, depending on the build and hub selection. I'm not sure of the exact weight of the M1900 hoops, but I'm guessing around 450 grams each, so the Arch EX will save a bit there.
> 
> Will I notice the difference on the long grinding fire road and single track climbs or during single track decents?


Depends on a few things just as everyone has pointed out (where the weight savings occurs in the lighter wheels - rims, spokes, and or hubs - as well as the quality of the wheel build for your riding weight and needs). But if your M1900 wheels weigh what the DT Swiss site says (880g front for QR/850g front 15mm TA + 1080g rear = 1930-60g - hell yes you'll feel a difference with lighter wheels.

The newly designed Arch rims look very nice. You get the slightly wider profile with the inner diameter of 21mm on the EX rims compared to the 19mm of the regular Arch rim. I have a set of wheels with the Crest rim (same inner 21mm width, but lighter).

Combined with some good rolling tires (Racing Ralph, IKON, Raven 2.2, etc...), a light cassette and the weight savings can add up enough for you to feel it on long grinding fire road and single track climbs.

I'd pick a good quality wheel builder who knows your needs, riding weight and can build the set for you.


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## D93 (Oct 19, 2011)

Looking at the DT Swiss website and comparing the specs on my rims with those on the site I think the M1900 rims are 480 grams. 

The ArchEX rim weighs 400 grams, so if I'm saving 80 grams per wheel of rim weight will the difference be noticeable? I'm sure there will be some spoke weight savings as well. I'm already running tubeless and will use the same tires.

Riding style is long climbs followed by technical descents.


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## BikeShopMonkey (Nov 18, 2010)

it's funny cause i spend some serious cash and go to extremes to save weight only to put it back on with stupid stuff like tools/tube/bell. 
i weigh my bike and in the end it comes out light weight, but not weenie weight.

then i image how heavy it would be if i didn't get the weight down in the first place and i would not be able to ride that heavy of a bike on most days.

so it does matter. every gram matters in the long run. make your bike as light and reliable as possible for more efficiency, handling and fun.

we can all ride a 40 lbs. bike, but maybe not as happily.


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## WarBoom (Dec 13, 2011)

First off I understand the physics between a bike wheel and a car wheel would use the same formulas and basic physical constraints but I didn't want to sound like a know it all jackazz which aparently you don't mind being portrayed as so...

Yep your math looks just fine
All I know is in a 10second car every 100lbs lost from the chassis is a 1/10sec (car length) and 30lbs lost on your wheel tire combo is 1-1.5/10sec. So please explain how it's not a 3x multiplier again. 
And I have personal experiance in it doin bracket racing. Going from a solid alum wheel to a 3peice magnesium wheel with a weight savings of 45lbs we can go from a +10.5 class to a +10.3 class with nothing but a wheel change. Same tire size, same day, nearly same temp.



craigsj said:


> Curious why you would think a wheel on a bike would work differently than one on a car. You think the physics is different?
> 
> The translational energy of a wheel is (1/2)mv^2.
> 
> ...


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## Guest (Feb 6, 2012)

WarBoom said:


> All I know is in a 10second car every 100lbs lost from the chassis is a 1/10sec (car length) and 30lbs lost on your wheel tire combo is 1-1.5/10sec. So please explain how it's not a 3x multiplier again.


Do you want me to quote myself? You can go back and read post #13 again if you like. The answer hasn't changed.



WarBoom said:


> And I have personal experiance in it doin bracket racing. Going from a solid alum wheel to a 3peice magnesium wheel with a weight savings of 45lbs we can go from a +10.5 class to a +10.3 class with nothing but a wheel change. Same tire size, same day, nearly same temp.


I would suggest you reconsider your belief that these things are things you "know". Simple physics tells use that the multiplier MUST be less than 2x, so anything you "know" says that it is 3x is clearly wrong.

Being called a "know it all jackazz" by people like you is a badge of honor. How could you even tell?


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## TigWorld (Feb 8, 2010)

D93 said:


> ...Will I notice the difference on the long grinding fire road and single track climbs or during single track decents?


I think you will notice a difference - climbing, descending and even bombing the rock gardens.

Here's part of a post I just made in the wheel forum thread in relation to thinner lighter spokes, but I think its applicable here too:

I have been building progressively lighter and lighter wheels over the years as well as running wider and wider tyres with lower pressure.

I have achieved lighter wheels, in part, by going from comps, to super comps and now revs. My rims have also got lighter along the way (mavic 717s 400g+, crests ~350g, podium MMXs ~290). I've also been going for lighter hubs (eg. rears - XTR 300g+, DT240s ~250g, A2Z ~250g, tune ~200g). My heaviest pair of wheels (1768g) is over 500g heavier than the lightest set (1240g). All wheels are 32h 3x laced.

What I've felt riding this range of wheels (and this is as subjective as it gets) using the identical tyres on each set of wheels (Conti X-King 2.4 front 28psi, Race King 2.2 rear 30psi) is:
- for just "cruising" around there is no perceivable difference between any of the wheels - you've really got to be pushing hard for any differences to become apparent;
- the narrow internal rim width of the 717s makes that wheelset (at 500g heavier) feel the flexiest and least accurate steering of all the wheelsets (although its clearly the strongest of all the wheelsets I own);
- the Tune/Revs/Podium MMX rear (676g) feels stiffer than the A2Z/SuperComps/Crest rear (776g) because of the larger/stiffer axle in the Tune rear hub (despite the thinner spokes and lighter components);
- I can run my rebound damping one or even two clicks faster with the lightest wheelset so the tyres stay in better contact with the ground particularly through braking bumps and rock gardens;
- the lightest wheelset is deflected off objects easier but it makes it easier to get the bike to go where I want it to as opposed to where the momentum of the wheels wants to take me - the lightest wheelset feels the most "accurate" to ride at speed.

From an engineering point of view, the lightest wheelset will clearly flex more than the heaviest wheelset, but from my experience the difference in flex (perhaps only fractions of a mm) is so far outweighed by the weightloss benefits to make the overall ride of the lightest wheelset superior. For riding hard and fast my lightest wheelset feels the most accurate and inspires the most confidence - something I would not have believed before I built and rode these wheels.


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## rydbyk (Oct 13, 2009)

Rotating weight is NOT all the same.

Hubs and tires are both rotating. Losing 90g off tires vs. 90g off hub are not the same. 

You will notice the tires before the hubs with regards to acceleration.

This is the primary reason that I9 has gotten rid of the nipples needed on the spokes. Instead, they bring the weight of the spoke down to the hub by adding a fatter threaded area of the spoke that threads into the hub = no 32 or more heavy nips way out there by the tires and rims.

.02


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## Jerome (Dec 21, 2003)

craigsj said:


> A grossly exaggerated rule of thumb. Rims, tires, and tubes count as 2x. Hubs are like frame weight. It is physically impossible for there to be a multiplier as high as 2x.
> 
> 200g at the rim can be noticeable but not dramatic.


The x3 multiplier for anything on the outer edge of the wheel (i.e. rim, tube (if any) and tire) is frequently used as a rule of thumb by the mags and other sources. I've never personnally measured the exact weight effect of such a change, but I can assure you that the difference can be felt and is huge in comparison with other weight reductions.


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## Guest (Feb 8, 2012)

Jerome said:


> The x3 multiplier for anything on the outer edge of the wheel (i.e. rim, tube (if any) and tire) is frequently used as a rule of thumb by the mags and other sources. I've never personnally measured the exact weight effect of such a change, but I can assure you that the difference can be felt and is huge in comparison with other weight reductions.


Ignorance can certainly be pervasive.  I haven't personally seen this mistake made in mags and other "sources", only here, but you may be right. It is, regardless, a mistake made by people who just make things up. 3x is BS that's just made up.

I've already provided the equations, known for centuries, along with the simple algebra needed to get the answer. This question is not subject to opinion or popular vote, it would be fair game in any first year high school physics class.


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## LukeGX (Oct 14, 2011)

WarBoom said:


> First off I understand the physics between a bike wheel and a car wheel would use the same formulas and basic physical constraints


I dont see how two different size wheels (race car and bike) can have the same factor for weight reduction in the wheel rim compared to the chassis/frame.

The further from the centre of the wheel the greater the effect of the weight saving so it stands to reason that larger wheels will have a larger factor and a greater weight saving effect in the rim.

Anyone who thinks that weight savings in the rim of small wheels (car) is the same as the weight saving in the rims of large wheels (bike) is obviously having trouble grasping the concepts of basic physics despite all the poorly presented algebra.

I took my valve caps off and now my bike is 56g lighter.


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## whtdel (Oct 24, 2008)

C'mon guys, Craigsj is right ... this subject has been covered in depth:
http://forums.mtbr.com/xc-racing-training/240-grams-rotational-600-gram-static-587734-2.html

And the physics that explains it all:
12. ROLLING, TORQUE AND ANGULAR MOMENTUM

If we remove the hub and spokes out of the picture, the equivalent factor would be 2x. On the other end, a plain disc will have an equivalent factor of 1.5x. Does a car wheel (with its hub) could be referred as a ring or a disc? If you agree with the later, than the equivalent factor would be closer to 1.5x.

But in fact, I wouldn't mix cars and bikes, since the physics surrounding cars happen at a much higher speeds, where aerodynamic' forces change drastically as the speed changes (by the square of speed), thus affecting lap times/performances by a large margin.


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## LukeGX (Oct 14, 2011)

whtdel said:


> And the physics that explains it all:
> ROLLING, TORQUE AND ANGULAR MOMENTUM


But the problem is it is all theory, they do mention radius as you would expect and that has a strong affect on the rotational energy even when mass stays the same. But no where does that site deal with reduction of mass on different parts of the 'disc'. The equations assume that mass is removed or added in equal proportions along the whole radius of the disc, which never happens in real life in cars or bikes.



whtdel said:


> But in fact, I wouldn't mix cars and bikes


I agree


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## Guest (Feb 15, 2012)

LukeGX said:


> But the problem is it is all theory...


How is that a problem? Explain what part of reality makes the theory invalid.



LukeGX said:


> ...they do mention radius as you would expect and that has a strong affect on the rotational energy even when mass stays the same.


It does not. That is shown clearly in example problem 12-1.



LukeGX said:


> But no where does that site deal with reduction of mass on different parts of the 'disc'. The equations assume that mass is removed or added in equal proportions along the whole radius of the disc, which never happens in real life in cars or bikes.


That's because concentration of mass at the circumference is worst case. As mass is distributed inward the multiplier becomes less than 2x. For bicycle wheels it is typically about 1.7x as has been said before.


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## litany (Nov 25, 2009)

craigsj said:


> How is that a problem? Explain what part of reality makes the theory invalid.
> That's because concentration of mass at the circumference is worst case. As mass is distributed inward the multiplier becomes less than 2x. For bicycle wheels it is typically about 1.7x as has been said before.


I think people who don't have a background in physics don't really understand how insanely accurate the theory is. It's so accurate it's what we use to design everything.

That web page isn't the end all of physics of rotating objects. The biggest problem is it's very difficult and time consuming to derive the rotational inertia of an object. You basically have a very complicated multivariable calculus problem where you have, even in something as simple as a spoke, a constant change of it's shape down the length of it (they are butted after all). When you finally spend a few days calculating the rotational inertia of every part of your wheel you realize that your result is hardly any different from just estimating with prederived shapes. Thankfully there are prederived lists of common object types and their rotational inertia which you can use to "build" a wheel. For example: List of moments of inertia - Wikipedia, the free encyclopedia

If you want to achieve a higher degree of accuracy you can add multiple calculations together. Estimate the rim as a hoop, estimate the hub as a solid cylider, estimate a spoke as a rod, estimate nipples as point masses, estimate the friction disc as a disc as a thick walled cylindrical tube etc. The more work you do the more accurate you can make your estimation. You can then go verify this estimation relatively easily and if you didn't make a mistake you should be able to get well within 1% of actual.

It's up to you to care enough to do the work. Generally though it's quite easy.

Let's take a real world scenario. I have DT XR 2.4D laced with supercomps to DT 240 hubs using DT al nipples. For instance lets say I want to upgrade to a fancy carbon rim, the XRC300. Spoke and nipple weights wont vary much between builds because I am using similar parts anyway. I want to know what effect a lighter hoop will have. Well I can estimate that to a very high degree of accuracy quite easily. The new rim will be about 100g lighter.

From that wiki page I=mr^2 Ok, we have a 26" wheel. How far is it actually from the hub to the center of the rim? 11" or 28cm. How much lighter is the new rim? 100g. Ok lets plug in and see what we get.

Our difference will be 78400gcm^2

Ok well what does that actually mean? How does that effect my bike? Well let's look at it this way, how much less work am I going to have to do now to accelerate my bike up to 10mph. Well that's just going to be however much work it would take to accelerate that hoop up to 10mph. What's that? That's how much energy that hoop will have at 10mph.

E = rotational energy + kinetic energy

I run race king tires. My race kings are 205cm around which means that at 10mph they are rotating at 13.7rad/s. Now lets add it all up: 1.735J

So losing 100g in one rim saves you 1.735J of energy to accelerate you from 0 to 10mph.

Seems low doesn't it? Wheels rotate really slowly is all.

So here we are. Answering the OPs question. We saved 100g in the best location possible in a wheel (all at the rim). That's 200g per wheelset and the difference was...minimal. You might notice it, a stiffer slightly lighter rim. I love light weight bikes. I'm currently saving up for some enve rims but don't get too carried away with thinking you're going to be like twice as fast or something.


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## Guest (Feb 16, 2012)

litany said:


> If you want to achieve a higher degree of accuracy you can add multiple calculations together. Estimate the rim as a hoop, estimate the hub as a solid cylider, estimate a spoke as a rod, estimate nipples as point masses, estimate the friction disc as a disc as a thick walled cylindrical tube etc


This is precisely where my 1.7x number comes from. I estimated the center of mass of a variety of bicycle wheels by weighing and measuring the individual parts. I modeled four wheels: a 700c road wheel, a 26er, a light and a heavy 29er wheel. The results didn't vary a great deal. The center of mass is about 70% of the way to the tread +/- 5%.

The extra energy needed to move rotating mass is WAY overblown. A 160 pound rider on a 30 pound bike that has 10 pounds worth of wheels has about 10% of his energy of motion tied up in the wheels with only half of that being rotational energy. Small differences in wheel weight, especially at the hubs, won't make a noticable dent. Sure, this is the WW section and everyone here is anal about weight savings, but it's good to keep things in perspective rather than exaggerate them out of control. Grams are grams except at the rim and tire where they are about twice as important, but the rim and tire aren' t places to skrimp on function either.


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## litany (Nov 25, 2009)

craigsj said:


> This is precisely where my 1.7x number comes from. I estimated the center of mass of a variety of bicycle wheels by weighing and measuring the individual parts. I modeled four wheels: a 700c road wheel, a 26er, a light and a heavy 29er wheel. The results didn't vary a great deal. The center of mass is about 70% of the way to the tread +/- 5%.
> 
> The extra energy needed to move rotating mass is WAY overblown. A 160 pound rider on a 30 pound bike that has 10 pounds worth of wheels has about 10% of his energy of motion tied up in the wheels with only half of that being rotational energy. Small differences in wheel weight, especially at the hubs, won't make a noticable dent. Sure, this is the WW section and everyone here is anal about weight savings, but it's good to keep things in perspective rather than exaggerate them out of control. Grams are grams except at the rim and tire where they are about twice as important, but the rim and tire aren' t places to skrimp on function either.


I agree completely. I wasn't trying to say your 1.7 number was wrong or anything, I was just explaining to the previous poster who seemed unsatisfied with where such numbers came from how he could model it himself.

A lot of people get hung up on accuracy without really understanding what that means or why it matters (or doesn't). When you're talking about only a 1.7J difference in a system that you're inputting 200-300J per second being off by 50% you're still only talking about a piddly amount of energy. I was trying to show how if you are super lazy with your estimate you can get to within 5-15% which will be around a tenth of a Joule. Obviously depending on how you set up your estimate you can ensure you will be on the high end which will add comfort: well I know I'll never get more than _this_. Let's not even get into anything _fancy _ like significant figures lol


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## Guest (Feb 16, 2012)

litany said:


> I agree completely. I wasn't trying to say your 1.7 number was wrong or anything, I was just explaining to the previous poster who seemed unsatisfied with where such numbers came from how he could model it himself.


Yes. People often get the concept right but have no feel for the magnitude of the differences. In this case it's remarkably small. Very accurate results can be obtained on wheels with a spreadsheet and a bit of time and parts information.

A similar argument with 29ers happens over and over again. The difference in mass is about 10%, the wheel size itself doesn't matter, and the ultimate difference to accelerate, at my rider weight, is about 0.5%, yet people still argue how sluggish 29er wheels are. Myths die hard.


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## litany (Nov 25, 2009)

craigsj said:


> people still argue how sluggish 29er wheels are. Myths die hard.


Maybe that has to do with gearing? You're turning a bigger wheel so it feels like your crank is accelerating slower despite the fact that your actual acceleration is unchanged?


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## Guest (Feb 16, 2012)

litany said:


> Maybe that has to do with gearing? You're turning a bigger wheel so it feels like your crank is accelerating slower despite the fact that your actual acceleration is unchanged?


Yes, that's true for some and there have been threads on that. I think it's always been part of the lore and 29er advocates have always apologized for it despite it being trivial. I suspect that early 29er wheels and tires were, in fact, heavy but that was before my time. It's true that the gearing commonly doesn't change even though it should.


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## LukeGX (Oct 14, 2011)

> It does not. That is shown clearly in example problem 12-1.





> When you finally spend a few days calculating the rotational inertia of every part of your wheel you realize that your result is hardly any different from just estimating with prederived shapes





> A similar argument with 29ers happens over and over again. The difference in mass is about 10%, the wheel size itself doesn't matter, and the ultimate difference to accelerate, at my rider weight, is about 0.5%,


If radius doesn't affect rotational energy then why does the weight loss factor increase as weight loss is moved to the outside of the wheel (as radius of weight loss increases).

If the equations are so accurate and they show negligible difference between a theoretical disc and an actual wheel then why bother trying to remove weight from the outside of the wheel? As others have stated, the accurate equations clearly show that there is negligible difference between a solid disc and a spoked wheel and therefore it should not matter where the weight is lost from.

Is it a common misconception that loosing weight from the rim has more affect than loosing weight from the hub? Or is it just a misconception that the affect is tangible?

Why do the equations say that the location of the weight loss can be avaraged across the disc but they also say that weight loss is increased by a factor of 1.7 at the rim?


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## Guest (Feb 16, 2012)

LukeGX said:


> If radius doesn't affect rotational energy then why does the weight loss factor increase as weight loss is moved to the outside of the wheel (as radius of weight loss increases).


The radius doesn't factor into the calculation of kinetic energy of a rolling wheel. That's why the radius of the wheel doesn't determine how slow it is to accelerate. The distribution of mass within the radius does matter but wheels with a larger radius don't have a distribution significantly different than smaller wheels.



LukeGX said:


> If the equations are so accurate and they show negligible difference between a theoretical disc and an actual wheel then why bother trying to remove weight from the outside of the wheel? As others have stated, the accurate equations clearly show that there is negligible difference between a solid disc and a spoked wheel and therefore it should not matter where the weight is lost from.


A conventional wheel and a theoretical disc are entirely different things. A real disc wheel is not the same as a ideal disc.

Why you "bother" to remove weight from the outside of a wheel, if you do, is it's that weight that matters most.



LukeGX said:


> Is it a common misconception that loosing weight from the rim has more affect than loosing weight from the hub? Or is it just a misconception that the affect is tangible?


Hub weight is not different than frame weight. Rim weight is worth twice as much. Many people overstate how much it matters.



LukeGX said:


> Why do the equations say that the location of the weight loss can be avaraged across the disc but they also say that weight loss is increased by a factor of 1.7 at the rim?


A real wheel can be modeled mathematically. It's not the equations that say that, it simply how it is. Weight loss at the rim is worth more than 1.7x, the 1.7x number is a typical number for wheelsets overall. If have abnormally light hubs and/or abnormally heavy rims and tires, your factor will be larger. It will NEVER be as high as 2x and certainly not 3x.

Take, for example, a 700g front wheel with a 450g rim. Add to that wheel 700g of tire and tube. As a rough approximation, the weight distribution as a percentage of radius will be (700 + 450) / (700 + 700) or 82%. The real number will be a lower mostly because the rim and tire and not concetrated at the outer radius. The rear hub, being heavier, lowers the number too. That why the number is closer to 70%.


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## litany (Nov 25, 2009)

LukeGX said:


> If the equations are so accurate and they show negligible difference between a theoretical disc and an actual wheel then why bother trying to remove weight from the outside of the wheel? As others have stated, the accurate equations clearly show that there is negligible difference between a solid disc and a spoked wheel and therefore it should not matter where the weight is lost from.


I'm not sure understand how it works. If you saw from my post I never modeled the wheel as a solid disc and never suggested doing so. As craigsj said you can mathematically model a real wheel. You can do it to a degree of accuracy that will make it very difficult and extremely expensive to experimentally find any difference between the predicted value and the actual value. This means the model is perfect for all intents and purposes. It all come down to how much work you are willing to put in. I however have argued that there is very, very little benefit and that being lazy is just fine.

Keep in mind the equations agree perfectly with reality for the things they model, obviously a rim is a more complicated shape than a hoop but it's so freaking close it doesn't matter. In any case you don't have a scale that can measure the weight of a rim to a thousandth of a gram so it _really_ doesn't matter. If you want to get super paranoid about it cut your rim open, measure the density and distribution of the material and you can create a huge equation to gain you that .0001kg m^2 (probably even less) of accuracy or something absurd like that. Don't forget to use your $5k scale, your $500 set of calibration weights and your $300 set of calipers. Then hope and pray your next rim is identical to the first (it wont be).

The equations show that removing weight from the rim is clearly the most efficient place to remove it. That's why I showed the difference a 100g reduction made at the rim. It showed the OP the maximum benefit. Stop thinking of the rim as a disc. Think of it as a collection of components--that is after all what it is. Also keep in mind that I can make a solid disc that has the exact same moment of inertia of a real wheel. That doesn't mean that it's the best way to do it.

That whole 1.7 factor is just a _super_ lazy way of doing it. Good enough to give you a pretty good idea but it's not the end all and be all.


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## BShow (Jun 15, 2006)

Kings are _not_ light hubs.


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## muzzanic (Apr 28, 2009)

I enjoyed reading this.


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## TigWorld (Feb 8, 2010)

The difference between accelerating a light and heavy wheel just once may be a piddling amount of energy, but ride 100km offroad and you will have accelerated those wheels thousands and thousands of times. Anytime you change speed, direction or elevation you are accelerating your wheels. All those little piddling differences add up. MTB riding is all about continuous changes in velocity.


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## LukeGX (Oct 14, 2011)

muzzanic said:


> I enjoyed reading this.


Me too.


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## championp (Feb 11, 2011)

You guys need to forget the math and ride your bikes. Lighter wheels make a huge difference. To the OP, yes you will notice the difference when you ride.


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## Electric Panda (Jan 8, 2006)

The interesting thing about this thread is that we should all try to get the science and forget the hype… while light wheels do make a ‘huge’ difference – how much of that ‘huge’ is hype and placebo effect and how much more energy are you actually using with a 100gr heavier tyres? Someone has done power testing on UST tyres v ‘normal’ tyres – I think I read one of LMN’s posts somewhere – it was not as much as many of us would think.

I am guilty of giving ‘11% further from the axis’ (with the additional weight) as one of the reasons why 29 wheels have tested 7% less efficient than 26 wheels… my bad… I do remember doing inertia calcs in first year but who remembers that stuff anyway?! It is probably why the elite XCO teams riding 29 wheels put up with skinny tyres and flexy wheelsets to get the weight down.


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## litany (Nov 25, 2009)

Electric Panda said:


> The interesting thing about this thread is that we should all try to get the science and forget the hype&#8230; while light wheels do make a 'huge' difference - how much of that 'huge' is hype and placebo effect and how much more energy are you actually using with a 100gr heavier tyres?


Exactly. We need to cut through the hype to get to the truth. I really wish someone would do actual testing on bicycle components. All the "pro reviews" are just so...useless. So little actual information.


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## Norm28 (Jun 15, 2011)

haha, this thread makes me feel stupid.........


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## phoeneous (Mar 7, 2005)

LukeGX said:


> Me too.


Me three. (7 years later)


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