theshoemaker

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?

MIN 

That statement is false.

All things being equal: the narrower the tire, the less rolling resistance.

johnny99

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.

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.

theshoemaker

I'd love to find it. Was the thread about rolling resistance or what? What would I search for?

Phantoj

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.

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.

Phantoj

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.

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.

Phantoj

I actually inflate my 23mm tires and my fatties (35mm) to about the same pressure. You got a problem with that?

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?

Turboem1

Wider tires have less rolling resistance. It has to do with the shape of the contact patch and amount of deflection. / Thread

DocRay

That's right, so if you want to go to thinner tires, they need to be very high pressure -tubulars, which is why most pro teams still run tubulars.

But compound matters as well. Harder rubber rolls better, but cornering and wet conditions suffer with harder rubber.

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.

DocRay

no, this is really about 19 vs. 23-25 mm.

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.

Phantoj

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)

MIN 

Ok, using that example... could you not draw the same conclusions?

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.

Fig335

Here we go https://www.rouesartisanales.com/article-1503651.html

MIN 

From that perspective, I would agree. But if you compare 23c to 35c at the same pressure and construction - the 23c would be less rolling resistance on your average road (or on a drum tester.) HOWEVER, if the road was poor or if you were cyclocrossing etc the 35c would be lower resistance.

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?

Murrays

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

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.

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.

MIN 

Good answer - sounds like the wider tires are both higher and lower resistance - condition dependant. My initial answer was based on my assumption of a 23c to 35c type of comparison, hence my answer. Brevity left no room for contingency scenarios which have since been raised...

urbanknight

Actually, I would argue that the ride would be better on the wide tire in that case. 90 psi on a skinny tire actually "feels" flat, which it kind of is because it's deflecting so much. It might be just as cushy as the wide tire, but it will feel like you're riding through mud and it wil bounce more. If you like the cushy ride, 35mm is a great choice. Since I want to go faster and don't mind a slightly harsher ride, I ride 23s pumped up to 115 psi. I still notice much more drag with those compared to the 23mm tubulars I used to race at 150 psi. Wow, what a difference!