# Lighter tire or less rolling resistance?



## bvber (Apr 23, 2011)

Which is more critical for increasing speed? I saw threads about different rolling resistance of narrower vs. wider tire and threads about reducing rotating weight to improve speed but those two categories play together when choosing tires. So which do you consider a priority if you want to go faster?


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## cxwrench (Nov 9, 2004)

light weight doesn't increase speed at all. you can _accelerate up to speed_ slightly quicker w/ a given amount of power, but that's all. once you're at speed, aerodymanics are the most important factor. lower rolling resistance will help you all the time.


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## Jay Strongbow (May 8, 2010)

It's kind of a false choice because most of your lighter tires are also the ones with lower rolling resistance.


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## bvber (Apr 23, 2011)

Jay Strongbow said:


> It's kind of a false choice because most of your lighter tires are also the ones with lower rolling resistance.


Wider tires generally weigh more than narrower one of the same model line. For example, Conti GP4000S, 23 is 25 grams lighter than 25 (Continental Bicycle -Grand Prix 4000 S) but I've seen rolling resistance chart posted on this forum which shows wider tire having less resistance. (Tire Rolling Resistance | Roues Artisanales)


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## MMinSC (Nov 19, 2011)

Riding more is critical for increasing speed...


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## Jay Strongbow (May 8, 2010)

bvber said:


> Wider tires generally weigh more than narrower one of the same model line. For example, Conti GP4000S, 23 is 25 grams lighter than 25 (Continental Bicycle -Grand Prix 4000 S) but I've seen rolling resistance chart posted on this forum which shows wider tire having less resistance. (Tire Rolling Resistance | Roues Artisanales)


yeah, true. Sorry, at first I understood the question a litte differently and thought you meant comparing different tires all together. If you look at a chart of tires of a particular size with the best rolling resistance you'll notice that non of them are boat anchors.
But anyway, as for the same tire in a different size, I'd assume the rider weight and air pressure would have to be factored in to so a blanket answer would be difficult.


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## bvber (Apr 23, 2011)

Jay Strongbow said:


> I'd assume the rider weight and air pressure would have to be factored in to so a blanket answer would be difficult.


Lets say a rider weighing 150Lbs who can get by with 23 wide tire but if the rotating weight isn't an issue for going faster, shouldn't that rider just get 25 wide or more for less rolling resistance? In such case, why aren't we seeing wide tires in "Tour de ..."?


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## RoadBoy1 (Oct 1, 2011)

bvber said:


> Wider tires generally weigh more than narrower one of the same model line. For example, Conti GP4000S, 23 is 25 grams lighter than 25 (Continental Bicycle -Grand Prix 4000 S) but I've seen rolling resistance chart posted on this forum which shows wider tire having less resistance. (Tire Rolling Resistance | Roues Artisanales)


The Tire Rolling Resistance chart is good. I first saw it about 6 years ago in an article by Leonard Zinn but I have to wonder is there an updated version of this? Some of these tires (Pro Race 2, Panracer Stradius Pro) don't exist anymore. If anyone knows of an updated version to this chart please post it. Thanks.


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## asgelle (Apr 21, 2003)

cxwrench said:


> light weight doesn't increase speed at all...


If you believe that, then you also have to believe that the coefficient of rolling resistance of tires, Crr, doesn't affect speed either since the force to overcome rolling resistance is the product of weight times Crr.


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## cxwrench (Nov 9, 2004)

asgelle said:


> If you believe that, then you also have to believe that the coefficient of rolling resistance of tires, Crr, doesn't affect speed either since the force to overcome rolling resistance is the product of weight times Crr.


explain it to me then. i thought lighter rolling components will only accelerate quicker, but not necessarily make for higher speed. would i be right in thinking that give a certain amount of power, lower rolling mass will attain higher speed and not just get there in less time?


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## NJBiker72 (Jul 9, 2011)

cxwrench said:


> explain it to me then. i thought lighter rolling components will only accelerate quicker, but not necessarily make for higher speed. would i be right in thinking that give a certain amount of power, lower rolling mass will attain higher speed and not just get there in less time?


You don't accelerate once unless you ride nothing but perfect flats. 

As for rolling resistance. Wider is less at the same pressure. Very big qualification..


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## rruff (Feb 28, 2006)

bvber said:


> Lets say a rider weighing 150Lbs who can get by with 23 wide tire but if the rotating weight isn't an issue for going faster, shouldn't that rider just get 25 wide or more for less rolling resistance? In such case, why aren't we seeing wide tires in "Tour de ..."?


Weight matters little. The tradeoff is between rolling resistance and aerodynamics. That is why all the new aero rims are designed to have a good profile with 23mm tires.


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## cxwrench (Nov 9, 2004)

NJBiker72 said:


> You don't accelerate once unless you ride nothing but perfect flats.
> 
> As for rolling resistance. Wider is less at the same pressure. Very big qualification..


did you read my first post? the OP asked about 'increasing speed', not 'accelerating quicker'. i know that lighter wheels accelerate quicker. will they go 'faster' all things being equal? as you said, very big qualification.


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## NJBiker72 (Jul 9, 2011)

cxwrench said:


> did you read my first post? the OP asked about 'increasing speed', not 'accelerating quicker'. i know that lighter wheels accelerate quicker. will they go 'faster' all things being equal? as you said, very big qualification.


You have to accelerate to go faster. Sure how much of a difference will vary but acceleration is a rather large factor in speed.


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## MMinSC (Nov 19, 2011)

NJBiker72 said:


> You have to accelerate to go faster. Sure how much of a difference will vary but acceleration is a rather large factor in speed.


Not really. They're related, but not mutually exclusive. If you aren't racing, it doesn't matter how quickly you get to 25mph, as long as you get there. 

To relate it to cars...

Torque is Acceleration
HP is speed


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## NJBiker72 (Jul 9, 2011)

MMinSC said:


> Not really. They're related, but not mutually exclusive. If you aren't racing, it doesn't matter how quickly you get to 25mph, as long as you get there.
> 
> To relate it to cars...
> 
> ...


True but that time getting up to speed is not time at speed, so it does slow your overall speed down.

How much then depends on a variety of factors. For me it is terrain. There is not a flat road around me. So it is all climbing/accelerating, then getting low for the descent. Then repeat. In each of those instances, the narrower tires are a benefit.


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## asgelle (Apr 21, 2003)

cxwrench said:


> explain it to me then. i thought lighter rolling components will only accelerate quicker, but not necessarily make for higher speed. would i be right in thinking that give a certain amount of power, lower rolling mass will attain higher speed and not just get there in less time?


You're mixing up two things; rolling resistance and rotational inertia. We're talking about rolling resistance, the retarding force from energy loss due to deformation in the tires. The force to overcome rolling resistance is the product of the coefficient of rolling resistance, Crr, times the normal force on the contact patch (equal to weight for both tires). So increasing weight has the same impact as incresing Crr, i.e, a 5% increase in weight on the tire is the same as increasing Crr of the tire by 5%. The power to overcome rolling resistance is the force time bike velocity. mgCrrV.

Rotational inertia comes into play when the bike is accelerating. Then in addition to the force to accelerate the mass of the system, there is an additional component due to increasing the rotation rate of rotating components. Unlike rolling resistance, though, this term is proportional to acceleration, not speed. As Kraig Willett andf others have shown, acceleration on a bicycle even in a full sprint is so slow that terms that scale as acceleration ar much smaller than those that go as velocity.


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## cxwrench (Nov 9, 2004)

asgelle said:


> You're mixing up two things; rolling resistance and rotational inertia. We're talking about rolling resistance, the retarding force from energy loss due to deformation in the tires. The force to overcome rolling resistance is the product of the coefficient of rolling resistance, Crr, times the normal force on the contact patch (equal to weight for both tires). So increasing weight has the same impact as incresing Crr, i.e, a 5% increase in weight on the tire is the same as increasing Crr of the tire by 5%. The power to overcome rolling resistance is the force time bike velocity. mgCrrV.
> 
> Rotational inertia comes into play when the bike is accelerating. Then in addition to the force to accelerate the mass of the system, there is an additional component due to increasing the rotation rate of rotating components. Unlike rolling resistance, though, this term is proportional to acceleration, not speed. As Kraig Willett andf others have shown, acceleration on a bicycle even in a full sprint is so slow that terms that scale as acceleration ar much smaller than those that go as velocity.


i definitely understand the difference between rolling resistance and rotational inertia. what i'm wondering about is if you had 2 sets of wheels, w/ the same exact shape/aerodynamic properties. say one pair weighed 1000g and the other pair weighed a pound more, so 1454g. if you had the same tires mounted on both and inflated them to the same pressure, obviously the lighter pair would accelerate quicker if the same force was applied. the question is would the lighter pair achieve a higher speed or would they both top out at the same speed? obviously we'd keep this to speeds attainable by a fit cyclist, so maybe 35-40mph. would aero drag come in to affect and limit the top speed of both pair to the same number? or does this even make sense?


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## MMinSC (Nov 19, 2011)

NJBiker72 said:


> True but that time getting up to speed is not time at speed, so it does slow your overall speed down.
> 
> How much then depends on a variety of factors. For me it is terrain. There is not a flat road around me. So it is all climbing/accelerating, then getting low for the descent. Then repeat. In each of those instances, the narrower tires are a benefit.


If you think a tire that weighs 50g more is really slowing you down, on any road, then a talk with a sports psychologist may be in order. It's 2.5 ounces, distributed around the circumference of the tire. Really not enough to make a difference...

And no, narrower are not a benefit. Once they wear, they become more squared off than a rounder profiled/wider tire. Ergo, your contact patch with the road is larger, thus, slightly slower....


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## cxwrench (Nov 9, 2004)

asgelle said:


> Final speed is when the power produced by the rider is equal to the power necessary to overcome all the retarding forces - drag, gravity, rolling resistance, drivetrain and other frictional losses. You say aero drag is the same in both cases, and we'll assume level ground so gravity doesn't enter the picture. Since the bikes are the same, frictional losses will also be equal. That leaves rolling resistance. You say you understand rolling resistance, that you know, as I wrote above, that power to overcome rolling resistance is Crr mg V where Crr is the coefficient of rolling resistance, and mg is the weight on the tire. It doesn't matter where that weight comes from. It could be the bike, the rider, the wheels or the tire. Since you're using the same tires, Crr will be the same for the two cases. That leaves the weight on the tires (I know it should be normal force, but we've limited ourselvs to level ground). It's not clear in your scenario if the heavier wheels raise the weight of the total bike/rider package or if the added wheel weight is offset by less weight somewhere else. We can consider both cases. In the first the weight of the total package is less so the rolling resistance force goes down. Therefore the power to overcome all the retarding forces goes down and the final speed goes up. If the total package weighs the same in both cases, the rolling resistance is the same and so is the final speed.
> 
> This paper presents the complete model. Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291. (Andrew Coggan) - Academia.edu and all the component parts are explained.


ok, i think i get the idea now. i'll check out that paper and see if i can understand it! :thumbsup:


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## asgelle (Apr 21, 2003)

cxwrench said:


> i definitely understand the difference between rolling resistance and rotational inertia. what i'm wondering about is if you had 2 sets of wheels, w/ the same exact shape/aerodynamic properties. say one pair weighed 1000g and the other pair weighed a pound more, so 1454g. if you had the same tires mounted on both and inflated them to the same pressure, obviously the lighter pair would accelerate quicker if the same force was applied. the question is would the lighter pair achieve a higher speed or would they both top out at the same speed? obviously we'd keep this to speeds attainable by a fit cyclist, so maybe 35-40mph. would aero drag come in to affect and limit the top speed of both pair to the same number? or does this even make sense?


Final speed is when the power produced by the rider is equal to the power necessary to overcome all the retarding forces - drag, gravity, rolling resistance, drivetrain and other frictional losses. You say aero drag is the same in both cases, and we'll assume level ground so gravity doesn't enter the picture. Since the bikes are the same, frictional losses will also be equal. That leaves rolling resistance. You say you understand rolling resistance, that you know, as I wrote above, that power to overcome rolling resistance is Crr mg V where Crr is the coefficient of rolling resistance, and mg is the weight on the tire. It doesn't matter where that weight comes from. It could be the bike, the rider, the wheels or the tire. Since you're using the same tires, Crr will be the same for the two cases. That leaves the weight on the tires (I know it should be normal force, but we've limited ourselvs to level ground). It's not clear in your scenario if the heavier wheels raise the weight of the total bike/rider package or if the added wheel weight is offset by less weight somewhere else. We can consider both cases. In the first the weight of the total package is less so the rolling resistance force goes down. Therefore the power to overcome all the retarding forces goes down and the final speed goes up. If the total package weighs the same in both cases, the rolling resistance is the same and so is the final speed. 

This paper presents the complete model. Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291. (Andrew Coggan) - Academia.edu and all the component parts are explained.


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## asgelle (Apr 21, 2003)

MMinSC said:


> If you think a tire that weighs 50g more is really slowing you down, on any road, then a talk with a sports psychologist may be in order. It's 2.5 ounces, distributed around the circumference of the tire. Really not enough to make a difference...
> 
> And no, narrower are not a benefit. Once they wear, they become more squared off than a rounder profiled/wider tire. Ergo, your contact patch with the road is larger, thus, slightly slower....


Before seeing a psychologist, you might want to talk to a physicist or at least consider the paper cited above. Everything you write above is refuted by data. I especially like the part where the shape of the tire affects the contact patch area.


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## MMinSC (Nov 19, 2011)

asgelle said:


> Before seeing a psychologist, you might want to talk to a physicist or at least consider the paper cited above. Everything you write above is refuted by data. I especially like the part where the shape of the tire affects the contact patch area.


You may want to read just what I wrote again...or learn to interpret the paper by Roues...

I AGREED with the idea that a wider tire yields a smaller contact patch, as the graphic wide tire/narrow tire shows.

A narrow tire, once it wears, with become more square, thus yielding a MUCH larger contact area with the road.


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## asgelle (Apr 21, 2003)

MMinSC said:


> I AGREED with the idea that a wider tire yields a smaller contact patch, as the graphic wide tire/narrow tire shows.


Yes. That's what's funny. That graphic, I do not think it means what you think it means.


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## phoehn9111 (May 11, 2005)

Please reference Leonard Zinn at Velonews for the rolling resistance and
moment of inertia information. I believe it is the closest to a definitive explanation
of the very complex dynamic in play.


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## asgelle (Apr 21, 2003)

phoehn9111 said:


> Please reference Leonard Zinn...


I would steer people away from Zinn, who has demonstrated minimal understanding, to Bicycling Science by Wilson and Papdopoulos. Amazon.com: Bicycling Science (9780262731546): David Gordon Wilson: Books


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## danl1 (Jul 23, 2005)

Originally Posted by *asgelle*  
_You're mixing up two things; rolling resistance and rotational inertia. We're talking about rolling resistance, the retarding force from energy loss due to deformation in the tires. The force to overcome rolling resistance is the product of the coefficient of rolling resistance, Crr, times the normal force on the contact patch (equal to weight for both tires). So increasing weight has the same impact as incresing Crr, i.e, a 5% increase in weight on the tire is the same as increasing Crr of the tire by 5%. The power to overcome rolling resistance is the force time bike velocity. mgCrrV._



Except, not. Increasing the weight of the entire bike+tire+rider system by 5% is equivalent to increasing the Crr of the tire by 5%. Your calculation is off by a few orders of magnitude. 

Unless we're talking about the tire rolling down the road by itself. But I'm not going to worry how fast that's going. It'll fall over soon enough.


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## bvber (Apr 23, 2011)

bvber said:


> In such case, why aren't we seeing wide tires in "Tour de ..."?


I think I found the answer to my own question. Tech FAQ: Again, bigger tires roll faster!


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## NJBiker72 (Jul 9, 2011)

MMinSC said:


> If you think a tire that weighs 50g more is really slowing you down, on any road, then a talk with a sports psychologist may be in order. It's 2.5 ounces, distributed around the circumference of the tire. Really not enough to make a difference...
> 
> And no, narrower are not a benefit. Once they wear, they become more squared off than a rounder profiled/wider tire. Ergo, your contact patch with the road is larger, thus, slightly slower....


As I said it is a matter of degree. And I know saying narrower is quicker is a sacrilege to some. That's why you see pro's on 32's.


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## asgelle (Apr 21, 2003)

danl1 said:


> Originally Posted by *asgelle*
> _You're mixing up two things; rolling resistance and rotational inertia. We're talking about rolling resistance, the retarding force from energy loss due to deformation in the tires. The force to overcome rolling resistance is the product of the coefficient of rolling resistance, Crr, times the normal force on the contact patch (equal to weight for both tires). So increasing weight has the same impact as incresing Crr, i.e, a 5% increase in weight on the tire is the same as increasing Crr of the tire by 5%. The power to overcome rolling resistance is the force time bike velocity. mgCrrV._
> 
> 
> ...


Weight ON the tire, not weight OF the tire. Go back and check the quoted text. (for that I had to take you off the ignore list?)


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## T K (Feb 11, 2009)

asgelle said:


> Final speed is when the power produced by the rider is equal to the power necessary to overcome all the retarding forces - drag, gravity, rolling resistance, drivetrain and other frictional losses. You say aero drag is the same in both cases, and we'll assume level ground so gravity doesn't enter the picture. Since the bikes are the same, frictional losses will also be equal. That leaves rolling resistance. You say you understand rolling resistance, that you know, as I wrote above, that power to overcome rolling resistance is Crr mg V where Crr is the coefficient of rolling resistance, and mg is the weight on the tire. It doesn't matter where that weight comes from. It could be the bike, the rider, the wheels or the tire. Since you're using the same tires, Crr will be the same for the two cases. That leaves the weight on the tires (I know it should be normal force, but we've limited ourselvs to level ground). It's not clear in your scenario if the heavier wheels raise the weight of the total bike/rider package or if the added wheel weight is offset by less weight somewhere else. We can consider both cases. In the first the weight of the total package is less so the rolling resistance force goes down. Therefore the power to overcome all the retarding forces goes down and the final speed goes up. If the total package weighs the same in both cases, the rolling resistance is the same and so is the final speed.
> 
> This paper presents the complete model. Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291. (Andrew Coggan) - Academia.edu and all the component parts are explained.


So are you saying a lighter wheel/tire package will attain/sustain a higher speed? All other things being equal.


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