# how much faster is slick compared to knobby?



## ivantcs (Jan 22, 2008)

Anyone know how much faster is slack than knobby?
Had a road ride on my knobby. 1 road bike and 2 mtb with slick
They were doing like 38km/h on flat and short climbs
The speed maintain for about 20km if not wrong.
One mountain bike and road bike took turns to lead
I draft all the way together with another mtb but got dropped at the last 2 or 3km.
Comparing a 1.25 or 1.5 slick to 1.95 knobby
The slicks are panaracer t-serve if not wrong, while i'm using maxxis ignitor.
Are slick much faster or am i just a slower rider?


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## SteveUK (Apr 16, 2006)

It would be very hard to quantify, but yes, a slick tyre will roll on tarmac considerably faster than a knobbly one, such is the increase in rolling resistance. Running the knobbly at as high a pressure as one can will improve tarmac performance, but still not to a point whereby it could compete with a slick tyre.


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## Atomik Carbon (Jan 4, 2004)

*Is this a serious question ?????*



ivantcs said:


> Anyone know how much faster is slack than knobby?
> Had a road ride on my knobby. 1 road bike and 2 mtb with slick
> They were doing like 38km/h on flat and short climbs
> The speed maintain for about 20km if not wrong.
> ...


Just pot on a set of 1.5" slicks and see how much faster you will be on the road. Now take those same slicks and ride off road.....:nono: .


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## Stevirey (Jul 16, 2005)

*slick vs knobby*

Slicks are obviously much faster on the street.And obviously no good on a trail.The best compromise I've come up with is Maxxis Holy Rollers.Fast on the street and good on the dirt.
The only down side is the weight. If it doesn't kill you,it will make you stronger.HaHa.


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## jeffgothro (Mar 10, 2007)

I spose as fast as you can pedal them...with me I've never felt slicks were faster, they just offerd less resistance, weather its a slick or knobbie doesnt matter to me, all thinings being equal I go just as fast on both usually.


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## Atomik Carbon (Jan 4, 2004)

*?????????????????????????????????*

with me I've never felt slicks were faster, they just offerd less resistance, [/QUOTE]

?????????????????????????????????????????????????????????????????????


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## jeffgothro (Mar 10, 2007)

YaMon said:


> with me I've never felt slicks were faster, they just offerd less resistance,


?????????????????????????????????????????????????????????????????????[/QUOTE]

Ever hear term its not the bike...but the rider...something like that. In other words, I can pedal or go just as fast on knobbies as I can on slicks (say like 90 PRPM -pedal revolutions per minut for example), I just have to work a little harder at doing it with knobbies. Got it?


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## highdelll (Oct 3, 2008)

well, i can ride uphill just as fast as i ride downhill - i just have to work harder


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## jeffgothro (Mar 10, 2007)

If you can maintain your pedal cadence at a steady RPM up hill as well as down hill at a constant speed then good for you, your a better man then me.  :thumbsup:


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## SteveUK (Apr 16, 2006)

"_all thinings being equal I go just as fast on both usually._"

But all "thinings" (great word, by the way!!) aren't equal, that's the point. By your reasoning, there's no point in putting air in tyres - just pedal harder.


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## Atomik Carbon (Jan 4, 2004)

*?????????????????????????????*



jeffgothro said:


> ?????????????????????????????????????????????????????????????????????


Ever hear term its not the bike...but the rider...something like that. In other words, I can pedal or go just as fast on knobbies as I can on slicks (say like 90 PRPM -pedal revolutions per minut for example), I just have to work a little harder at doing it with knobbies. Got it?[/QUOTE]

I'm NOT touching this one ....????????????????????????????????????????????


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## eminefes (Sep 11, 2008)

I'm not familiar with what kind of slicks you can get for mountain bikes, but if you can get a skinny pair that inflates to around 80-100 psi, that should make a nice difference. You can probably expect to see your average speed increase by a couple mph.

Or buy a road bike and really see your speed increase. :thumbsup:


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## jeffgothro (Mar 10, 2007)

SteveUK said:


> "_all thinings being equal I go just as fast on both usually._"
> 
> But all "thinings" (great word, by the way!!) aren't equal, that's the point. By your reasoning, there's no point in putting air in tyres - just pedal harder.


I'm talking more about terrain or thats what I had in mind when I wrote that...like riding on the street for example (which is where I do alot of my riding). I honestly dont feel a difference in my speed weather I'm on slicks oe knobbies, you follow? If anyone doesnt believe or agree with me, thats fine, but your not me, when I ride I usually keep a steady cadence, that cadence dictates how fast I go, NOT the tires I happen to be using.

Tire pressures are relitive - if it takes 70lbs to make my knobbie rock hard, thats what I put, if it takes 100lbs to make my slick rock hard, thats what I put. This why I seldom to almost never use slicks, I prefer the added traction and stability of knobbies.


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## bigpedaler (Jan 29, 2007)

I have one bike, MTB, and a majority of the riding I do is on pavement. I commute, pay bills, take the kids to the burger joint, etc. on two wheels. I ride trails when I have the time and opportunity. Well, in '07, I had zero opportunity, so in '08, I tried out some Intense MicroKnobby 2.25's. Near as I will get to true slicks.

The Micros rolled at least half a gear faster than the Hutch Spiders they replaced; less overall effort for the same speed, and where my extra effort got burned up was in wind resistance (I block a LOTTA wind, lol). But the Micros are absolute sheee-iiittt! on dirt! Now that the weather is going away again, I put the Spiders back on for the snow. I may or may not wear out the Micros come spring, dunno. But the OP question depends 100% on riding surface.


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## Circlip (Mar 29, 2004)

Some knobbies are actually fairly quick rolling (for a knobby) due to tread pattern, but perhaps just as importantly casing construction. Some full slicks are actually quite slow (compared to other slick tires) for the same reason - casing construction. Many full slicks in a 26" format have casings that are highly reinforced since they are made for commuting, and consequently casing design priortizes durability. That extra reinforcement consumes measurable amounts of energy e.g. more rolling resistance to deform the casing as the wheel rolls.

I have a Powertap power meter on my mountain bike, and have observed with quantifiable numbers of watts in versus speed, that it is actually possible to have a knobby tire that has less rolling resistance than a slick tire. However, that will be the rule rather than the exception.

More pressure in a knobby isn't always a guaranteed answer either. Depending on the specific arrangement of tread blocks, some knobby tires are actually more efficient on the road at lower than max recommended pressures, since it can bring extra rows of blocks into play to create a more continuous rolling succession of blocks. Once again, I have verified this quantitatively.

At higher speeds, especially approaching and over 25mph, wind resistance is by far a greater impediment to speed than rolling resistance. Proportionately, the effect of adding a bit of rolling resistance isn't very consequential at those higher speeds, for anyone who actually has the fitness to maintain those speeds for any duration with the less aerodynamic MTB riding position.

Lastly, if you have a narrow slick then you will have reduced wind resistance versus a wider tire, again really only relevant at higher speeds. A wider slick won't have the same aero advantage.

The obvious comment to all of this is that if you really want to go fast, get a road bike. However, if that's not an option or else if you simply prefer riding a mountain bike on the road then some of the information above may be helpful. From a training perspective, it's all a function of watts/power in at the cranks. How fast you travel as a result (due to bike/tire differences, etc.) is somewhat irrelevant, although most people do find the extra speed and smoothness to increase the fun factor for road riding.


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## Ericmopar (Aug 23, 2003)

Generally speaking, the slicks are faster, but there are exceptions. 
A few months ago, I put Bontrager Cruizer 2.1 tires on my old Trek beater bike and it now feels like I'm riding into a headwind all the time. 
Those Bontrager slicks are so bad, that I can climb and cruise just as fast on pavement, with my 6" San Andreas DHS, with 2.4" full knobby Maxxis tires. 
Before, when I had 1.5" invert tires on the old Trek, I could pedal along at least two gears higher on less energy.


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## pisiket (Sep 19, 2006)

Great post!



Circlip said:


> Some full slicks are actually quite slow (compared to other slick tires)


I always thought that that was the reason for my not feeling any difference with slicks at all. I had gone from Conti. vertical pro tires to armadillos... Of course this is just my feeling, I did not measure anything.

I absolutely hated the flimsy look of slicks on my 26" mountain bike as well.  Yuck!

Ali


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## Bo55Diesel (Jun 12, 2008)

I put slicks on my bike and my average speed increased by about one m.p.h. on my timed rides.


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## pursuiter (May 28, 2008)

~20% faster.



-----------------------------------------------------------------------------------------------------
83% of all statistics are made up on the spot


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## Circlip (Mar 29, 2004)

pursuiter said:


> ~20% faster.
> 
> -----------------------------------------------------------------------------------------------------
> 83% of all statistics are made up on the spot


That figure and your footnote re: statistics match up very nicely. :thumbsup:


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## Steve from JH (Dec 30, 2003)

*The physics of rolling resistance*

The main cause of rolling resistance is somewhat surprising. At least I was surprised when I researched the subject. It has to do with the hysteresis of the materials used.

Put in plain english, hysteresis means that the rubber of the tire resists being flattened out into a contact patch with more force than it exhibits when it snaps back from being flattened out. The part of the patch ahead of the axle is being flattened; the part behind the axle is snapping back. This means that the tire pushes down on the ground with more force ahead of the axle than behind. The point of maximum downward pressure is thus ahead of the axle when the wheel is rolling. It's right below the axle when the wheel is still.

So the main point of resistance by the ground to the load on the wheel is ahead of where the load comes down to the ground through the axle. This creates a reverse torque on the wheel, trying to turn it backwards.

It follows that the longer the contact patch is, the farther forward the point of maximum resistance to the load is, and the more rolling resistance there will be from this hysteresis effect.

If all other things are equal except that you have knobs on one tire and a slick tread on the other, the contact patch will have to be longer for the knobby tire in order to get enough rubber on the road to support the load. Thus more rolling resistance.

Another factor is that the rubber of each knob is much thicker than the rubber on the slick tire. More rubber sitting on the casing means more hysteresis and more rolling resistance. Tires have less rolling resistance as they wear out because of this factor.

As for wind resistance of the tire, surprisingly it's what's happening to the air inside the tire that makes the most difference, not what's happening outside. As the wheel rolls along, the air inside is subjected to turbulence much like what happens when a propellor cuts through the air. So the larger the overall volume of air inside the tire, the more turbulence and resistance. That, I think, is one reason road tires are so narrow. It's not primarily to make them cut through the air better, although that's a factor. It's that they simply contain less air.


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## Circlip (Mar 29, 2004)

pisket said:


> I always thought that that was the reason for my not feeling any difference with slicks at all. I had gone from Conti. vertical pro tires to armadillos... Of course this is just my feeling, I did not measure anything.


There's a very timely note on Velonews' tech guru Leonard Zinn's column today that talks specifically about Armadillos, or any other tire with a similar casing construction;

http://www.velonews.com/article/85518/technical-qa-with-lennard-zinn---fight-flats-lose-speed


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## Steve from JH (Dec 30, 2003)

Circlip said:


> There's a very timely note on Velonews' tech guru Leonard Zinn's column today that talks specifically about Armadillos, or any other tire with a similar casing construction;
> 
> http://www.velonews.com/article/85518/technical-qa-with-lennard-zinn---fight-flats-lose-speed


I think what is happening when the tire is not supple enough--as in the example Zinn is discussing--is not strictly speaking increased rolling resistance. Instead what you're getting is a series of minor slippages as the tire very briefly loses its grip on the road surface. The same thing can happen from overinflating a tire.


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## ivantcs (Jan 22, 2008)

Steve from JH said:


> The main cause of rolling resistance is somewhat surprising. At least I was surprised when I researched the subject. It has to do with the hysteresis of the materials used.
> 
> Put in plain english, hysteresis means that the rubber of the tire resists being flattened out into a contact patch with more force than it exhibits when it snaps back from being flattened out. The part of the patch ahead of the axle is being flattened; the part behind the axle is snapping back. This means that the tire pushes down on the ground with more force ahead of the axle than behind. The point of maximum downward pressure is thus ahead of the axle when the wheel is rolling. It's right below the axle when the wheel is still.
> 
> ...


Interesting. :thumbsup:


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