http://forum.slowtwitch.com/cgi-bin/gfo ... age=unread

Thoughts?

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I firmly believe that unless you actually test on an imperfect surface, that atleast somewhat replicates the surface of a real road, you've got nothing. How the tire deforms to asphalt and how it deforms to a constantly smooth surface, I believe, must make a difference. I don't think you can just multiply numbers thinking that a tire that deforms well to a roller will deform exactly equally well to a real road.

But that's just my thoughts, I believe the whole roller-deal is pretty flawed. Now if they would add a layer of tarmac on a roller, that would be interesting.

I have no scientific background for this, just my personal 2 cents.

EDIT: Here's an idea, put a piece if innertube over the roller, cover it in some appropriate glue, and roll it in small pebbles (aquarium bottom material stones?). Repeat until it's covered in an even tarmac-like surface. Repeat whole crr test. Now that would be of real interest.

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Roadbike
Kinesis RaceLight T2

Mountainbike
Van Nicholas Zion Ti

drop the psi too. @120 you'd have no teeth left round here, and bugger all grip either.

DMF, agreed. Those tests have to be read with the artificial setup in mind. There was a thread about tyre width and rolling resistance recently:
viewtopic.php?f=3&t=111506

That said, the Conti Attack not only comes out very well in the test, it rode nicely in the real world for me too (compared primarily to other Conti offerings).

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Bikes: Raceur, Beateur

Hi,



There is no reason for that. It would only change the numbers but not the rankings per se.

IOW a topformer in the lab should perform equally well on a road.

Ciao,

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By that reasoning, if a steel wheel tests best on a steel drum, it will also have the least rolling resistance on the road. I don't think that's the case.

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Bikes: Raceur, Beateur

Hi,



It's just not practical as the steel wheel would destroy the road surface which is inherently much softer.
That's why steel wheels are put on steel rails.

Not sure if some of the tyre models tested by Ron also figure in Al's database but if they are then these should occupy roughly the same spots in the ranking.
Rolling resistance will always vary with load, tyre pressure and to a lesser extent temperature. Keeping the load under the tyre steady instead of varying it with a road surface that is not smooth is not going to change the ranking of the test results.
If it did then introducing "a road surface" would make the test method only valid for that particular strip of road and not much else.
So, no point in doing that as you then should also test all tyres at varying tyre pressures and temperature and so on. Sure the rolling resistance figures will change but not the ranking give or take the odd exception or two...

Ciao,

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Being a snob is an expensive hobby.

DMF, disagree. Or better, I agree with your reasoning, in that it makes sense. Reality just turns out to be counter-intuitive.
Tom Anhalt, Andy Coggan have done regression field testing that confirms Crr-rollers has a consistent and linear relation to Crr-road. Other testing has confirmed this, but I can't refer to those by name right now. A factor of 1.4 to 1.5 to adjust Crr-rollers to road seems about correct, but the main point is the consistent nature of the factor. [edit: like Frank writes above] Also, while it is a good point that roller tests often are done with higher pressures than you'd run on the road, the numbers remain valid, as in, the tires stay in the same order. [Tom A., Tour Magazin].
Speaking of Tour, their tests are also comparable to this one (in their own lab-setup, as well as on the old Conti test-drum they used, albeit with their own testing/measuring gear). Tubulars are a different matter, but I suspect this has a lot to do with glueing technique.

Interestingly, this is yet more confirmation that you can't determine how 'fast' a tire is by feel. Of course, with all the different tires out there, it is well possible that some have a roller handicap/advantage. That just hasn't been found in any testing I know of.

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Allright, I'm willing to change my mind if someone actually has shown correlation with real world road testing (I'll take your word for those tests). It just seemed to me like this test takes no account for how the casing reacts to the small irregularities in the road, and one (well, me) thinking that different casings are better or worse at this, but the steel drum would never show that.

I guess that might mean, either there are no differences between different tyres casings, or it just doesn't matter for crr performance (but might matter for ´feel´).

_________________
Roadbike
Kinesis RaceLight T2

Mountainbike
Van Nicholas Zion Ti

Hi,



I hear what you're saying. IMO the good results of the Conti tyres (despite their rather stiffish casings) are attributable to two factors: the Vectran anti-puncture belt which is extremely supple (as in almost not being there) and the Black Chilli Compound.

Ciao,

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Being a snob is an expensive hobby.

Maybe I'm just not seeing it, but does anyone know if these tires were tested under load. How the casing deforms determines the size and shape of the contact patch, which has a huge effect on rolling resistance.

All this test does is put them in some sort of Crr ranking. It can't seperate out the effects of carcass TPI and rubber compound. But this test did not try to do this. Also this chap did it for free and has published data. Surley he is to be commended for that. I commend him for the time and effort put in the data published.

I do not think the small irregularites would change how the tyres rank. It would change the crr values measured but real world road data is difficult to do as air conditions are rarely constant ans how would you seperate the effects of air resistance, drive train drag e.t.c. from rolling resistance? You can't and it will be difficult to ride at a absolutley constant speed. The diemeter of the rollar used will also change the absolute crr vaules reported but the order the tyres rank in should remain the same. A big roller is better than a small one.

The tests have to be done this way and if you do not believe the results it like you don't believe in Physics. The data provides a ranking little else as on the road the vaules reported will be different.

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Another consideration is how aerodynamic a tire may be. A while back I was conversing with Chris from Flo wheels and he told me he was very surprised when they did their wind tunnel testing that the Vittoria Corsa Evo 320tpi had 50 more grams of drag over the Pro Race 3.

_________________
-For my next trick I will set myself on fire!
-This board and the world in general would be a much nicer place if everyone could just take themselves a little less seriously.
-Sticky Fingers John Rockefeller
-First one over the cliff wins!

http://www.trainingandracingwithapowerm ... -part.html"

http://xkcd.com/54/

A rough roller would not change the order of the tires. But if you were doing a pressure/Crr test, it will certainly change where the pressure increase no longer equals lower rolling resistance. That would be an interesting test, and seeing if tires w different constructions have different pressure sweet spots.