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PostPosted: Fri Feb 08, 2013 9:45 am 
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Location: Cambridge, New Zealand
I use a surface roughness factor in course modelling that scales Als CRR figures - I've not done formal testing of scenarios but once I've evaluated the surface the models work very well in predicting the effect of changing tyres for different riders.

And in formal testing I've seen predictable (per the AFM figures) changes in CRR when I've changed tyre set ups since the previous session (testing focussed on Aero so any CRR info is incidental).

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Posted: Fri Feb 08, 2013 9:45 am 


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PostPosted: Fri Feb 08, 2013 1:33 pm 
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sedluk wrote:
The test is fundamentally flawed. There is no correlation between a tire on a smooth surface versus a rough surface. Roads are never a smooth surface so the results are meaningless.


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

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Last edited by acoggan on Fri Feb 08, 2013 3:07 pm, edited 1 time in total.

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PostPosted: Fri Feb 08, 2013 1:42 pm 
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Location: Netherlands
Sometimes, I despair.
If you don't bother to read a thread, especially one that isn't 45 pages long, don't post.
And if some PhD shows up to post links to actual data, the last thing you'd want to do is actually follow it. I do apologise, don't let yourself be confused by the facts and go ride those Tufos on the real road, because they feel fast.

[edit: and the good doctor just beat me to it, thanks again]

@WMW, thanks for the explanation, I didn't know those Conti's are all the same casing.
@Fdegrove, I for one, am not able to avoid 'high-puncture risk' areas, they just happen. But I agree that side-wall protection is a somewhat questionable feature on a racing tire.

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PostPosted: Fri Feb 08, 2013 2:06 pm 
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Flawed logic to say take something that isn't remotely like the group you're comparing and it will behave differently, therefore invalidating the test.

There is within that thought though a serious point on the confidence you have to have in the established correlation between lab and real world performance for the actual population of tyres under test.


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PostPosted: Fri Feb 08, 2013 2:29 pm 
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The physics of what WNW/rruff has done is well known and his tests are vailid. His errors are low as he has stated makig his data even more vailid. The method that WNW has used is how tyre manufacturers for bike, motrocycles and tyres make Crr measurements. The same method is used in university Labs. It is a verified method and provide real world ranking. The Crr value generated will be specfic to the test conditions and the same tyre will show differet Crr values on the different road surfaces but with the correction factor the Crr values reported will be pretty close to what is seen in the real world.

Those that claim this test is not vailid do not understand the phyics of what is being done. Before dismissing this very time consuming work done for free and published for free may be do abit of readiing. Bicycling science Ed 3. is a good place to start.

Thanks WNW.

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PostPosted: Fri Feb 08, 2013 5:29 pm 
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DMF wrote:
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´).



You don't have to change your mind about anything. But, you should consider that it is a "constant". Which means, it really doesn't matter what road surface it is tested on, as long as every tire is tested in nearly identical fashion on the same surface.

Real world? Well, we know things in real life are vastly different. But, we need to have some constant and relative environment which to test and compare.

Then, we have to make assumptions that no matter what surface is used, to a point, that the results should be similar as a comparison.

The point being, it is better having something as a comparison, then nothing at all and guessing.

As Einstein once stated: "As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality."

So will we ever have a definitive? Not really when it comes to an actual race/performance at a specific point in time on a certain day. But at least it is something!


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PostPosted: Fri Feb 08, 2013 6:30 pm 
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drop the psi? 120 is not much for TT, is it?


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PostPosted: Fri Feb 08, 2013 6:53 pm 
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tetonrider wrote:
while this example is extreme, this leads me to believe that there is somewhere along the spectrum between "smooth road" and "world's worst road" where the correlation to the rollers breaks down. would it be on chip seal? that's real world where i ride and race. also, there are different grades of chip seal.


On a smooth hard surface, a solid steel wheel would have the lowest resistance. But none of the tires we use are trying to emulate that. Rather the best tires on the rollers and on the road are the ones that are thinnest and most flexible.

All of these tires lose energy the same way... via flex of the casing and tread, hysteresis, and friction. This is what I'm measuring via rollers, and scaling to the road. There is another component though, that is related to road roughness... how easily the tire conforms to bumps and how much vibration is transferred. So if one tire requires 90 psi to ride as smoothly as another at 100 psi, then the later would have an additional bonus on the road vs rollers. In this case you normalized the roughness component by altering the pressure. The hysteresis component always rises if pressure is dropped. Usually the good tires on the rollers tend to be smoother on the road also, but this isn't always the case.

If you'd like to scale Crr for different pressures, use (p1/p2)^.44. So comparing 100 and 90 psi, the factor is 1.047.

If I was doing this, however... I wouldn't do it. I ride on roads that are often pretty rough chipseal, and use 90psi front and 100 psi rear. I didn't notice any of these tires riding substantially different than the others. I expected the Vittoria Evos to ride smoother than the Contis... but I didn't experience it. I would need to do a blind test on the same section or road and switch back and forth several times.

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PostPosted: Fri Feb 08, 2013 10:11 pm 
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sedluk wrote:
The test is fundamentally flawed. There is no correlation between a tire on a smooth surface versus a rough surface. Roads are never a smooth surface so the results are meaningless.

As a thought experiment, take a hard solid rubber tire. It will have incredibly low resistance on a smooth surface and incredibly high energy loss on a rough surface. With this test, the solid tire would still be predicted to be the most efficient on a rough surface. Sorry but completely flawed.


Why not take your theory one step further and let us all know how would you perform a meaningful test? Don't keep all that useful knowledge only to yourself.


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PostPosted: Fri Feb 08, 2013 10:15 pm 
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bm0p700f wrote:
The physics of what WNW/rruff has done is well known and his tests are vailid. His errors are low as he has stated makig his data even more vailid. The method that WNW has used is how tyre manufacturers for bike, motrocycles and tyres make Crr measurements. The same method is used in university Labs. It is a verified method and provide real world ranking. The Crr value generated will be specfic to the test conditions and the same tyre will show differet Crr values on the different road surfaces but with the correction factor the Crr values reported will be pretty close to what is seen in the real world.

Those that claim this test is not vailid do not understand the phyics of what is being done. Before dismissing this very time consuming work done for free and published for free may be do abit of readiing. Bicycling science Ed 3. is a good place to start.

Thanks WNW.


Exactly! :thumbup:


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PostPosted: Fri Feb 08, 2013 10:20 pm 
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The potential difference is if the bike were allowed to bounce on bumps. With rollers it's locked in. A bare rim would do well on rollers but on a real road the bike would be bouncing so much resistance would be high. Yet the BikeTechReview/Wattage crowd has tested this, and for reasonable tires at the same pressure the rolling resistance tests work fairly well. That said it's clear that cyclocross world championships aren't won on high-pressure tires so for truly rough surfaces suspension effects are clearly important.

Anyway, great work. I'm glad to see people doing measurements like this. I'd love to see a latex-versus-butyl test to verify Al Morrison's conclusion that latex is faster.

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PostPosted: Sat Feb 09, 2013 12:46 am 
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Location: Belgium
Hi,

Quote:
I expected the Vittoria Evos to ride smoother than the Contis... but I didn't experience it. I would need to do a blind test on the same section or road and switch back and forth several times.


Many years ago I did these kinds of experiments just so I had a feel of whether or not claimed and tested stuff was corelating with what is experienced on a road.
My conclusion was that if you put a bog standard butyl inner tube in a Vitto Evo CX much of the advantage of its high TPI casing is going down the drain. Especially so at highish tyre pressures.
Put in a latex inner tube a la Vredestein, which is structurally very similar to what you'd find inside a high-end tubular, et voila, all is plush and comfy.
Do the same with a Conti clincher and the only thing you may notice is the lower weight of the latex inner tube. Vredestein hits the scales at a meager 55g, not all latex inner tubes are that much lighter than a standard butyl one.

I tried literally dozens of various latex inner tubes, basically anything I could buy, the most comfortable one was by far one made by or for Pariba (a defunct company bought up and chilled by Vred IIRC). It wasn't light at all weighing 80g a piece or thereabouts but it sure made the latex effect obvious.

I'm no longer preaching (People like Casran, Sharkman, Kraaf, et all can testify) the use of latex inner tubes as a general cure as I'm and always have been well aware that their use is not really universal in that they need the utmost care to mount and are by no means ideal for descending at high speeds among other things when mate to wheels of the clincher persuasion.
Still, for the courageous ones, the benefit is there to be had.

So, knowing all this I switched to tubulars where, in my mind, I could have my cake and eat it too.
Well, yes, I admit I am very lucky to live in Europe where we can source the creme de la creme of tubs without paying through the nose.
Where I do my shopping a Conti or Schwalbe would cost me 10 to 20 % more than a Veloflex Carbon so why bother?
A totally different situation from the US and even here the numbers of good sources are dwindling.

That being said, perceptions can be misleading sometimes. There is no doubt in my mind whatsoever that even the stiffish Contis would show a reduced Crr when outfitted with a latex inner tube. Latex being that much more compliant than butyl it should. Just plain common sense.
Not sure anyone would feel the difference with the possible exception of the carbon saddle/thin chamois crowd perhaps. Still, if it's measured than it is there....

Point is, when in doubt measure it. All test results I've ever seen always turned out to be in favour of latex inner tubes.
Whether or not one actually feels the difference then becomes rather irrelevant.
Common sense says latex rules.

Common sense also dictates higher tpi casings should perform better in the real world under the same circumstances as lower ones at the same pressures and increasingly so when pressure is lowered or load is increased. No ?

Sometimes I get the impression that some tyres are purposely designed to measure well but do not perform all that well in the real world.
OTOH I know tyres that do not care much about measurements but that have traditionally performed extremely well in the real world.

I'm well aware it all seems pretty contradictive but as explained before the blindingly fine test results of some tyres may well stem from elsewhere.
Hence perhaps the intuitive reaction of some to the obvious?

Quod erat demonstrandum.... Or Pandora's box reloaded.

Ciao, ;)

FLASH:

http://www.bike-eu.com/Home/General/2013/1/Vittoria-Opens-Nanographyte-Compound-Factory-1153769W/?cmpid=NLC|Bike%20Europe|22-jan-2013|Vittoria%20Opens%20#8216;Nanographyte

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PostPosted: Sat Feb 09, 2013 2:12 am 
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acoggan wrote:
http://www.trainingandracingwithapowermeter.com/2010/12/crr-roller-vs-field-test-results-part.html" onclick="window.open(this.href);return false;"
;
I still dunno why the hell Michelin stopped making the Pro 2 Race; probably coz all you weight weenies kept saying they were too heavy :D

I reckon they've acknowledged their balls-up by making the Pro 4 a lot like the Pro 2


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PostPosted: Sat Feb 09, 2013 5:27 am 
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Is there a new Conty Attack?! I'm confused, but that's easy to do.

I'm thinking I might run the ~165g black chili Attack up front and an Ultremo ZX out back.

Years back, I happily ran the pre-BC Attack / Force combo. Went with Ultremos to save weight and allegedly improve Crr.

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Posted: Sat Feb 09, 2013 5:27 am 


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PostPosted: Sat Feb 09, 2013 1:33 pm 
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My observation, is that low rolling resistance often is linked to less then ideal traction, specifically not holding corners at speed. I would add, that the ability to deal with road imperfections is important for most of us and vital to the equation for overall tire performance. The test does not address overall performance, only rolling resistance. We must always consider the limits of a test, it is our eagerness to extrapolate, beyond the scope of this limited type of test, that inaccuracies and false conclusions occur.

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