Tire Rolling Resistance Study

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wpccrunner
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by wpccrunner

VeloNews posted an interesting new study on tires and rolling resistance

http://velonews.competitor.com/where-th ... tires-fast

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DMF
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by DMF

Interesting read, but WHY do they test these things at 116psi when IME most seasoned cyclists on clinchers will be riding closer to a 95-105psi range? GP4000s on intermediate quality tarmac at 116psi seems off the mark IMO...

As for those who've looked at the aerodynamics/windtunnel-tests of tires, I really wonder what the actually fastest tire would be,when aerodynamics and crr is both taken into account... I'd take a bet a Conti 4000 would be riding in circles around a cotton specialized? ;)

OK, I realize this comes off a bit much as a pro conti post, but I really just mean to point out the whole story...

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by SLCBrandon

:popcorn:

Grill
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by Grill

I ride all 23mm tyres at 115-120psi on the road. For TT's it's higher and on track it's waaaaaay more.

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by mimason

Grill, what is your weight?

I'm 83kg and typically ride 100-105/105-110 when on 23s. Somtimes if I'm in a hurry and did not fill up I'm likely 90/95 at the lowest.

Interesting that Specialized was high in the ranking likely due to all the Continental expertise going over to the darkside.

bm0p700f
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by bm0p700f

Different widths too. Who would ride a 28mm tyre at 116 psi. Drop the pressure and the rolling resistance goes up a bit.

Grill I used to ride tyres that width that hard and oh my I am so glad I use wider tyres at lower pressures now. While there is no right and wrong on this I couldn't go back. If I want to remind my self what 23mm tyres are like at 110 psi I take my old vitus out and I am reminded to put it away for a while again.

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by djconnel

I was shocked a tubeless with sealant came out on top! When tubeless first came out I expected they'd have the best rolling resistance since there's no tube-tire interface but they initially had really stiff sidewalls to suppress burping/blowout and so they tested slow.

On the pressure: safest to just go with constant pressure since the effect of pressure differs depending on the road surface: not so much for rolling resistance proper but for an additional energy dissipation mechanism of bouncing the rider which in the standard model is still folded into Crr. You won't measure that on a test rig. I suppose they could have come up with some scheme to scale pressure based on 1/diameter or whatever but then you're depending on pump linearity and not just precision.

I think the best pressure depends on if you're interested in time trials and hillclimbs when you'd naturally run higher pressure or in road racing when you'd run a bit lower. And of course it depends on body mass. I'm 58 kg and ride 140 psi in hillclimbs. Most of the time I'm 80 psi.

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by Grill

mimason wrote:Grill, what is your weight?

I'm 83kg and typically ride 100-105/105-110 when on 23s. Somtimes if I'm in a hurry and did not fill up I'm likely 90/95 at the lowest.

Interesting that Specialized was high in the ranking likely due to all the Continental expertise going over to the darkside.


78kg. 115-120 on 23c, 100-110 on 25c, 130-140 on 20c tubs, and 175+ on the track.

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by BeeSeeBee

DMF wrote:As for those who've looked at the aerodynamics/windtunnel-tests of tires, I really wonder what the actually fastest tire would be,when aerodynamics and crr is both taken into account... I'd take a bet a Conti 4000 would be riding in circles around a cotton specialized? ;)


Tom Anhalt actually looked at that with data from Specialized. The GP4000 (23mm) does in fact beat the Specialized tires aerodynamically, but the Cotton Turbo pretty handedly overcomes that disadvantage between +/-10° of yaw thanks to its rolling resistance.

From http://bikeblather.blogspot.com/2014/07 ... -town.html:

Image

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DMF
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by DMF

Very intriguing chart, I wonder how the SW cotton gets such low aero numbers when it is basically the same shape/construction as a Vittoria Evo Corsa, that in FLO's aero testing did absolutely horrible results...?

Image

100 grams of drag roughly equates to 9-11 watts at 40kph AFAIK...

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by BeeSeeBee

The plot I posted is a combination of aero drag and rolling resistance, the Cotton Turbo is a pretty poor aero performer, but as Tom mentions, "Crr can make up for a great deal of aerodynamic sins." Click the link and you can see just the aero performance.

Using the aero rule of thumb (0.1 lbs (50 g) of drag (@ 30 mph) = 0.5 s/km = 5W = 0.005 m^2 CdA = 0.0005 Crr) and going off just the aero data, I see the Cotton Turbo about 4.5W slower than the GP4000S at 10° and 9W slower at 15°. The Vittoria is about 8W slower than the GP4000S at 10° and ~10W slower at 15°. There's clearly some texture on the side of the Cotton Turbo, perhaps it helps reduce flow separation, at least at lower yaw angles?

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by CPongpanich

This is a genuinely interesting article. Thanks for posting.

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DMF
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by DMF

I see the VN article puts the crr difference at only 2,3 watts per tire, or roughly 5 watts for the pair, between the SW cotton and GP4000s...

Somehow the figures of the SW cotton being superior in an aero/crr combination doesn't make sense to me?

Of course we are ATM speaking of numbers from three different sources, and at the brink of margin of error...

And also. Gp4000s obviously has some serious puncture protection compared to the flimsier cottons, so where is the Attack/Force combo in all of this? Seems like the most potential rival to the cottons?


Edit, seems GP4000 fairs a bit better than the GP Attack at high yaws, but Attack has it slightly in the lower yaws where we are comparing the SW cottons, and AFAIK the Attack has lower crr than the GP4000 too...

Image
Last edited by DMF on Wed Nov 11, 2015 9:04 pm, edited 4 times in total.

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by bsavery

Couple thoughts. When do we start claiming velonews was paid off by specialized???

Second, doesn't really make a different in RR but seems odd they did all this testing then relied on the manufacturers numbers for width and weight.

But the numbers are more interesting in the comparison between clincher/tubeless/open tubular. Surprised tubeless did so well.

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BeeSeeBee
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by BeeSeeBee

DMF, note that the VeloNews test uses a 25mm GP4000S tire, whereas the Specialized data uses a 23mm tire, which is good for north of 1W (see here: http://www.conti-tyres.co.uk/conticycle ... 014_UK.pdf . An aside: interesting that the Schwalbe One performs worse the wider you go :noidea:). Also, like you said, there's certainly going to be some error involved because we're grabbing stuff from all over the place, but it certainly opens up a can of worms about equipment selection depending on what your expected wind angles are going to be.

But this is the stuff I love, we're starting to include multiple parameters in tests that we used to look at with a pretty singular focus. e.g. We'd only look at aero, or only at CRR, but now we're looking at the combination of the two to find the overall best. Similar to how watts to spin is starting to enter the conversation about wheel aerodynamics in a way that I don't remember in the past. Science slowly trudges forward :thumbup:

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