- misunderstanding rolling resistance -
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- misunderstanding rolling resistance -
I must not understand rolling resistance. I went to the LBS to get some new tires. Just as I was running out of time I asked some questions about tire width and was told that “the wider the tire, the less rolling resistance”. I thought that rolling resistance was resistance caused by surface area contact and that the more of it you have the more resistance you get. No? What am I missing here?
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Sheldon Brown's web site has a good argument on why "all things being equal" is a bogus argument. When you are dealing with different sized tires, all things are never equal.
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There was a thread a while ago that had a website that talked about rolling resistance. It said that too and I didnt understand it either.
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Originally Posted by Fig335
There was a thread a while ago that had a website that talked about rolling resistance. It said that too and I didnt understand it either.
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https://yarchive.net/bike/rolling_resistance.html
All things equal, rolling resistance is better with fatter tires.
But fatties suffer in these areas (generally all things are NOT equal):
1. Larger area means higher stress in the tire for the same pressure. So fat tires often are rated for lower pressure than thin tires.
2. Fat tires usually have less flexible sidewalls - is this because they are cheaper, junkier tires, or because they have to be stronger to handle higher stresses? Who knows, but this increases rolling resistance.
3. Fat tires make for a larger aerodynamic cross-section, so aero drag is higher with fatties.
All things equal, rolling resistance is better with fatter tires.
But fatties suffer in these areas (generally all things are NOT equal):
1. Larger area means higher stress in the tire for the same pressure. So fat tires often are rated for lower pressure than thin tires.
2. Fat tires usually have less flexible sidewalls - is this because they are cheaper, junkier tires, or because they have to be stronger to handle higher stresses? Who knows, but this increases rolling resistance.
3. Fat tires make for a larger aerodynamic cross-section, so aero drag is higher with fatties.
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Originally Posted by MIN
That statement is false.
All things being equal: the narrower the tire, the less rolling resistance.
All things being equal: the narrower the tire, the less rolling resistance.
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Well, I think the contact area has to be equal for either size of tire. Contact area will be load/pressure regardless of tire size.
But a fatty casing doesn't have to flex as much to get the same amount of contact with the ground. And the flex of the casing is not entirely elastic; energy is absorbed in that flexing, causing rolling resistance.
But a fatty casing doesn't have to flex as much to get the same amount of contact with the ground. And the flex of the casing is not entirely elastic; energy is absorbed in that flexing, causing rolling resistance.
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Originally Posted by urbanknight
INCORRECT. Read post by phantoj above. The reason for this is that (assuming equal tire pressure) the wider tire will bulge less on the ground, resulting in a smaller contact patch while the narrower tire will have to bulge more to support the same amount of weight. This was discussed in a thread recently (I'll see if I can find it) where someone drew a picture to demonstrate.
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Originally Posted by johnny99
Equal tire pressure means that the fatter tire is over inflated. That is why "all things being equal" is a bogus argument. If you over inflate the the skinny tire, then its rolling resistance will go down, too. Over inflated tires give you a harsher ride that can actually slow you down on rougher roads.
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Originally Posted by urbanknight
INCORRECT. Read post by phantoj above. The reason for this is that (assuming equal tire pressure) the wider tire will bulge less on the ground, resulting in a smaller contact patch while the narrower tire will have to bulge more to support the same amount of weight. This was discussed in a thread recently (I'll see if I can find it) where someone drew a picture to demonstrate.
One is 23c at 100psi using Rubber compound/belt combo X.
Second is is 2" wide at 100psi using the same Rubber coupound/belt combo X.
You are saying the 2" wide tire will have less rolling resistance?
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Wider tires have less rolling resistance. It has to do with the shape of the contact patch and amount of deflection. / Thread
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Originally Posted by urbanknight
INCORRECT. Read post by phantoj above. The reason for this is that (assuming equal tire pressure) the wider tire will bulge less on the ground, resulting in a smaller contact patch while the narrower tire will have to bulge more to support the same amount of weight. This was discussed in a thread recently (I'll see if I can find it) where someone drew a picture to demonstrate.
But compound matters as well. Harder rubber rolls better, but cornering and wet conditions suffer with harder rubber.
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Originally Posted by Phantoj
I actually inflate my 23mm tires and my fatties (35mm) to about the same pressure. You got a problem with that?
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Originally Posted by MIN
You have two slicks:
One is 23c at 100psi using Rubber compound/belt combo X.
Second is is 2" wide at 100psi using the same Rubber coupound/belt combo X.
You are saying the 2" wide tire will have less rolling resistance?
One is 23c at 100psi using Rubber compound/belt combo X.
Second is is 2" wide at 100psi using the same Rubber coupound/belt combo X.
You are saying the 2" wide tire will have less rolling resistance?
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i was told by the owner of my LBS that the reason you dont see 700x18 tires as much anymore is because slightly larger tires (700x20) were found to have lower rolling resistance AND a more cush ride.
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https://sheldonbrown.com/brandt/rolling-resistance.html is actually a lot better link than the jumble of Jobst that I linked to in Post #6. Also https://sheldonbrown.com/tires.html#rolling (see Width and Pressure)
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Originally Posted by DocRay
no, this is really about 19 vs. 23-25 mm.
I guess I'm not understanding the some of the peripheral issues of the arguement. For the sake of argument, controls must be in place. Even if in reality a larger tire would be run at lower pressures, for the sake of comparison two tires of different sizes needs to be considered at the same pressure, same construction.
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Originally Posted by ivegotabike
i was told by the owner of my LBS that the reason you dont see 700x18 tires as much anymore is because slightly larger tires (700x20) were found to have lower rolling resistance AND a more cush ride.
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Originally Posted by johnny99
It's not my problem. You're the one who is defeating the purpose of fat tires by over inflating them. I am kind of surprised that a 35mm tire doesn't blow off your rim at 100 psi, though.
Why shouldn't I? I find the ride quality to be good. Is the ride of a fat tire at 90 psi the same as a skinny tire at 90 psi?
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As others have pointed out, wider tires at the same pressure and design have lower rolling resistance, but narrow tires can run at higher pressures which can make the ride less comfortable.
Other factors include weight and air resistance where narrow tires win out.
OTOH, narrow tires are more prone to pinch flats and higher pressure tires are more prone puncture from road debris.
Personally, I ride Michelin ProRace2 23x700 inflated to 110. I find that's a good compromise of the various factors.
-murray
Other factors include weight and air resistance where narrow tires win out.
OTOH, narrow tires are more prone to pinch flats and higher pressure tires are more prone puncture from road debris.
Personally, I ride Michelin ProRace2 23x700 inflated to 110. I find that's a good compromise of the various factors.
-murray
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I found a link to an explanation posted by dannoxyz https://www.rouesartisanales.com/article-1503651.html I was slightly off on my explanation. The contact patch is about the same in surface area, but the narrow tire has to deflect more, which causes more rolling resistance.
Well, I wasn't trying to argue that wide of a range, but yes actually.
If the cross sections are round as most bike slicks are (no shoulders and no flat tread section) and they have the same everything else, the 2" will have less rolling resistance. You have to understand geometry, though. A perfect arch only contacts a flat surface on a pinpoint, so the contact patch is almost nill in either case. When you apply weight to the tire, it gets compressed and causes the contact patch to get larger. The wider tire can spread its weight along its width while the narrower tire has to use its length, which is curved (because it's a wheel). This causes the narrower wheel/tire to have to flatten itself more to reach that contact patch. Either way, the contact patch is about the same, but the narrow tire has to flatten itself as it rolls while the wide tire can stay more round. Because of that, the road creates more friction in flattening the narrow tire than it does with the rolling wide tire.
Now, as mentioned above, you can't run 100psi on a 2" wide tire, and I imagine the differences between a 23mm tire and a 28mm tire are very subtle, especially since some of that is offset by the aerodynamic drag and weight differences.
Originally Posted by MIN
You have two slicks:
One is 23c at 100psi using Rubber compound/belt combo X.
Second is is 2" wide at 100psi using the same Rubber coupound/belt combo X.
You are saying the 2" wide tire will have less rolling resistance?
One is 23c at 100psi using Rubber compound/belt combo X.
Second is is 2" wide at 100psi using the same Rubber coupound/belt combo X.
You are saying the 2" wide tire will have less rolling resistance?
If the cross sections are round as most bike slicks are (no shoulders and no flat tread section) and they have the same everything else, the 2" will have less rolling resistance. You have to understand geometry, though. A perfect arch only contacts a flat surface on a pinpoint, so the contact patch is almost nill in either case. When you apply weight to the tire, it gets compressed and causes the contact patch to get larger. The wider tire can spread its weight along its width while the narrower tire has to use its length, which is curved (because it's a wheel). This causes the narrower wheel/tire to have to flatten itself more to reach that contact patch. Either way, the contact patch is about the same, but the narrow tire has to flatten itself as it rolls while the wide tire can stay more round. Because of that, the road creates more friction in flattening the narrow tire than it does with the rolling wide tire.
Now, as mentioned above, you can't run 100psi on a 2" wide tire, and I imagine the differences between a 23mm tire and a 28mm tire are very subtle, especially since some of that is offset by the aerodynamic drag and weight differences.
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Originally Posted by urbanknight
I found a link to an explanation posted by dannoxyz https://www.rouesartisanales.com/article-1503651.html I was slightly off on my explanation. The contact patch is about the same in surface area, but the narrow tire has to deflect more, which causes more rolling resistance.
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Originally Posted by Phantoj
The 35mm tires are rated for a max pressure of 90 psi, and I usually run them at that pressure.
Why shouldn't I? I find the ride quality to be good. Is the ride of a fat tire at 90 psi the same as a skinny tire at 90 psi?
Why shouldn't I? I find the ride quality to be good. Is the ride of a fat tire at 90 psi the same as a skinny tire at 90 psi?
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