Rolling resistance of wide tires

Exactly ... I guess that's my point, there are a lot of factors to be considered and you can drive yourself nuts trying to account for them all. So IMHO you are better off running something with good puncture protection that you are used to and handles predictably vs going for the fastest rolling tire and risking a puncture or a crash. The time you gain in rolling resistance might be lost on the side of the road. 

Xenophon wrote:It's an interesting topic but imo trying to identify let alone factor in all variables and their interaction becomes so complex as to be unrealistic.  And even if you'd manage that herculean feat, it would still provide a relatively one-dimensional simplification of the real world.  A tire with extremely low rolling resistance won't help if it slips or flats easily.

Of course, everyone keeps telling themselves that tiny technical differences can radically affect outcomes and that's what makes the industry sell very expensive bikes and expensive, specialized tires with marginal applications (I'm looking at you, Heine) to 49 y/o dudes such as myself whose BMI is usually north of optimal and who never, ever can exploit those marginal benefits. 

Pick the tire and tire pressure in function of the terrain you ride, your willingness to accept discomfort, the noise level that you wish to accept and the risk of slipping/flatting that is acceptable to you etc.  There is no magic formula and even if there was one, you'd have to swap tires almost every single ride in function of weather and the type of surface ridden to fully exploit it.  Subjectively fastest tire I ever rode was great in dry conditions but offered the grip of teflon on melting ice in the wet.  Sure didn't help my speed.  Most comfy tire I ever rode (Compass Barlow Pass in extralight) was like a magic carpet, so smooth.  But the carpet drank sealant like a russian sailor drinks vodka and unfortunately it decided to blow off the rim.  Twice.  

<a wrote:

Tire width choice, like every other equipment decision in cycling, is a compromise trying to choose the best width/tread/pressure for the type of terrain and conditions you are going to encounter over the entire ride.... for something like Unbound this can be quite the challenge where your dealing with lots of hard-packed smooth and fast gravel, blown-out loose dry stuff, mud, square-edged water bars, and probably some mud. So the goal is to choose the best tire that will be good for most conditions.

The problem with BRR is that they are doing the test on a smooth drum, so yes, that will give you a rolling resistance for "ideal" conditions, but when you're riding off road only a small portion of that is "ideal". Also, rolling resistance is just part of the equation, if your pressure is too high your energy is going vertically instead of propelling you forward, so running a wider tire at lower pressure will allow some deformation. 

My understanding is that wider tires have the same rolling resistance at the same pressure as their narrower counter parts, but most people won't, or shouldn't be running the same pressure on a wider tire. 

 

Here's a good article by René Herse on this subject... granted, they are not impartial. https://www.renehersecycles.com/why-wider-tires-are-not-slower/ 

Angstrom wrote:...
What exactly does it mean to have "the same tire in a wider size"?  You can't just scale every dimension up.  Stiffness goes as the cube of thickness, so small changes could have significant effects.  And if you change some dimensions but not others, is it really the same tire?...

AnyAndAllRoads wrote:

And I think that's where the drum tests fail. Running a single tire on the equivalent of a flat road is just not the same as riding 2 tires, especially uphill where more of the weight is on the rear tire. I'm not sure there really is a good way to test one tire vs another other than actually riding them - and that gets expensive.

I understand that a (relatively) smooth drum test is not a good predictor of performance on rough surfaces when it comes to rolling resistance vs. pressure.  There’s plenty of data on impedance losses to support that.

But between similar tires tested under similar conditions?  I find it hard to believe that a tire that’s a slug on the drum will be a rocket on the gravel, or vice versa.

I think it’s reasonable to look towards the top of the lists at BRR or other tests, and choose the highest-rated tire whose other characteristics fit your needs.  

Angstrom wrote:

I understand that a (relatively) smooth drum test is not a good predictor of performance on rough surfaces when it comes to rolling resistance vs. pressure.  There’s plenty of data on impedance losses to support that.

But between similar tires tested under similar conditions?  I find it hard to believe that a tire that’s a slug on the drum will be a rocket on the gravel, or vice versa.

I think it’s reasonable to look towards the top of the lists at BRR or other tests, and choose the highest-rated tire whose other characteristics fit your needs.  

 

pushstart wrote:I think both are true in practice.  The wider tire will be less likely to flat just by nature of volume alone, but also different tire brands do sometimes change the design of wider tires in the same model lineup (without having investigated deeply, WTB Exposure jumps to mind).

But there are certainly examples where this does not happen, so I think there's plenty of opportunities to compare construction apples to apples. 

Angstrom wrote:

I understand that a (relatively) smooth drum test is not a good predictor of performance on rough surfaces when it comes to rolling resistance vs. pressure.  There’s plenty of data on impedance losses to support that.

But between similar tires tested under similar conditions?  I find it hard to believe that a tire that’s a slug on the drum will be a rocket on the gravel, or vice versa.

I think it’s reasonable to look towards the top of the lists at BRR or other tests, and choose the highest-rated tire whose other characteristics fit your needs.  

 

mmalin wrote:I appreciate the discussion going on here.

My opinion is that there is a coupling between an ideal tire width for a given course/terrain and the average speed that a rider can sustain over the magnitude and type of vertical deformations on a given course. This theory is roughly described in the Speed vs. Terrain vs. WAM figure shown in the following 3T blog post:

https://blog.3t.bike/2020/06/14555/what-gravel-tire-do-i-need-gravel-bike-tech/

I think the point that this blog tries to help the community understand is that tire selection should also be dependent on the size of the engine, aka fitness of the rider, for a given event. If you are unfit for the demands of the event, a small% decrease in rolling resistance is not worth the trade off in loss of suspension in a narrow tire

How does the group feel about this theory?

shiggy wrote:

Bad example. WTB makes the Exposure (and other models) with the same three constructions in each size

The Exposure comes in two widths – 30mm and 34mm. While both versions share the same tech and intentions of endurance road and gravel racing, the two tires are each distinct due to very different tread layouts. The 30mm Exposure uses a fast rolling smooth center tread, with a simple and low-profile set of file-tread shoulders for a bit of traction when the corners get loose. The 34mm Exposure on the other hand uses a more narrow slick center with siped sides, that transition into progressively taller diamond tread supported on the shoulders by larger, widely spaced lugs. It definitely looks like it will be more suited for riding in the loose stuff.

barrows wrote:"Offsetting pressure there's also a geometric factor.  Consider riding on a reasonably uniform field of broken glass, i.e. any paved road near my home.  In a given distance a wider tire will roll over a larger number of shards so will be more likely to encounter one large and sharp enough to puncture the tire."

The above is an incorrect POV:  The wider tire will be less likely to flat in this scenario, because the load is spread out.  The load at any given point of glass shard is lower, so there is less force at that point working to puncture the tire.  This factor is one of the reasons wider tires, at lower pressures (lower pressures allow the tire to conform around the point of a road, or a piece of glass) are used for MTB racing, where course often have pointy, sharp rocks.

pushstart wrote:

I guess they do now?  They didn't used to.  Well, the sidewall construction may have been the same, but the 34 looked like a completely different tire.

From  https://bikerumor.com/wtb-brings-more-widths-and-tread-to-road-trail-with-new-riddlers-and-exposures/