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PostPosted: Mon Mar 03, 2014 3:58 am 
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wassertreter wrote:
The thing is, this sort of random variance can be handled quite well using statistical methods. If they are doing due diligence -- which they claim -- then the findings can still be relevant.


Sure. Say running each configuration 10 times on different days and averaging the results. But he didn't claim to have done anything of the sort or make any mention of variance. BTW, that makes an already tedious and long test 10x as long and tedious.

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Posted: Mon Mar 03, 2014 3:58 am 


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PostPosted: Mon Mar 03, 2014 11:26 am 
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WMW: he does indeed claim statistical analysis on his blog:

One important question was still open: Did the results represent real differences in tire performance, or was there too much noise in the data? After all, even slight changes in rider position, a tiny gust of wind, or other factors might influence the results. To check this, Mark, who has a Ph.D. with a Minor in Statistics, did a sophisticated statistical analysis. He found that our results were “statistically significant.” (Basically, he compared the data from the three runs of the same tire with the data from different tires. The variations between runs with the same tire were much smaller than the variations between different tires.) This means we really did measure differences in tire performance. (Many studies skip this step, but it’s crucially important.)


PS: Since this has been going back and forth a bit, I feel the need to disclose that I have never run Grand Bois or similar tyres, and will probably not do so any time soon. But the discussion is interesting nonetheless.

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PostPosted: Mon Mar 03, 2014 4:40 pm 
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wassertreter wrote:
WMW: he does indeed claim statistical analysis on his blog:The variations between runs with the same tire were much smaller than the variations between different tires.)


Think about that for a second. All that means is that the results were not totally random. In other words the scatter caused by random variables did not *completely* overwhelm the real Crr differences. It definitely does *not* mean that his conclusions were valid.

If he wants to convince anyone, then let's see the raw data and analysis.

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PostPosted: Mon Mar 03, 2014 10:42 pm 
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Sure, seeing the data would go some way. Or maybe just a number for what "much smaller" means, for starters. On the other hand, you hardly ever see the raw data, be it Crr tests from some german mag, or Cervelo, Zipp, younameit aero tests. In the end it (almost) always comes down to how much you trust the tester and publisher in methodology and conduct.

Personally, I don't think the work Heine does would be second rate, compared to the high gloss publications.

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PostPosted: Tue Mar 04, 2014 12:34 am 
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No, you usually don't see raw data... but when the test has such large sources of potential error, and reaches odd conclusions... I don't believe the results otherwise.

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PostPosted: Tue Mar 04, 2014 1:04 am 
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Hi,

The odd conclusion being that butyl inner tubes reduce RR.
Knowing that the influence on RR of a latex inner tube has barely any measureable impact on RR that is an odd conclusion indeed.
Especially so when one considers the fact that in all other RR tests carried out so far over the past decades and beyond, tubulars and clinchers confounded, the top performers invariably where the ones that had a latex inner tube.

This begs the question: how on earth did they arrive at such a conclusion?

One other question that pops up which may have been answered in the Heine article is what butyl inner tube did it take to beat all other contenders?

To my mind, and I think I've mentioned it before, the only way to beat the RR record holder is to build the same tyre and do away with the inner tube altogether. After all, wasn't that one of the "raisons d'etre" for the tubeless tyres in the first place?

Ciao, ;)

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PostPosted: Wed Mar 05, 2014 6:32 pm 
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Heine's superior butyl tube was just an ordinary one... not even thin or special.

I've tested the fattest latex (old Vreds that weigh > 100g) and thinnest latex tubes (new Vreds)... no difference in Crr. Latex returns nearly all of its deformation energy. There is a reason they use it for slingshots and spear guns. Make rubber bands out of latex and compare their launch performance to butyl... no comparison.

There is no advantage to going tubeless since you need something to seal the tire anyway... and latex adds essentially nothing to Crr.

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PostPosted: Fri Mar 07, 2014 12:53 am 
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WMW wrote:
dunbar42 wrote:
He claims they only did this on mornings with perfectly calm winds and that they (later in a wind tunnel) confirmed the rider was able to hold a very consistent position. We're talking about an 800ft/245m rolldown test on a fairly modest grade hill so I doubt aerodynamic drag is all that significant.The test seems at least as relevant (if not more so) as the steel drum Crr tests which only tell you how a tire behaves on perfectly smooth surfaces.


Sure... no wind (0.0 mph... really?) and a perfectly consistent position... right. If you are able to compute the effect of these variables, please do so and get back to us. I did... and I don't believe any of the results.


Fine, but I hope you aren't putting too much stock in steel drum Crr tests either. I could make an equally snarky comment like "real world roads are never as smooth as steel drums." That doesn't leave us with much other than anecdotes about how amazingly fast a tire feels.


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PostPosted: Tue Mar 11, 2014 12:47 am 
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Metal drums are perfectly fine for comparing the hysteresis losses of different tires and tubes. The factor they miss is suspension losses... vibration caused losses which increase with pressure, and result in an optimum pressure for any given tire depending mostly on road conditions.

The important point is whether there is any reason to suspect that the relative ranking of tires on rollers will change on a real road. It could happen if there was some reason why a low hysteresis tire somehow transmitted high vibration on the road (relatively).

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PostPosted: Tue Mar 11, 2014 1:01 am 
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Hi,

Quote:
The important point is whether there is any reason to suspect that the relative ranking of tires on rollers will change on a real road.


That would not make any sense provided the only thing you're testing is rolling resistance.
Whether or not you carry out such a test on a steel drum or on a real road should not change the ranking of the DUTs.


Quote:
That doesn't leave us with much other than anecdotes about how amazingly fast a tire feels.


How a tyre "feels" is not relevant. It may feel either way but that does not make it any faster or slower. You can't rely on perception.

Ciao, ;)

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PostPosted: Wed Mar 12, 2014 2:31 am 
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fdegrove wrote:
Whether or not you carry out such a test on a steel drum or on a real road should not change the ranking of the DUTs.


I'm not certain of that. One component of resistance on the road will be vibration... which ends up being dissipated and lost. This isn't measured at all on the roller.

It might be tricky to put into a resistance value, but it should be easy enough to measure the vibration. Instrument a bike with motion and vibration sensors, and send the rider around a loop... swap tires, change pressure, try different surfaces, etc... see what difference it makes.

At any rate regarding the *tubes*... I don't think latex tubes are going to be generating more vibration at all.

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PostPosted: Wed Mar 12, 2014 2:05 pm 
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The ideal test would be a road rolldown with rider in a vacuum.

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PostPosted: Wed Mar 12, 2014 4:47 pm 
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Hi,

Quote:
I'm not certain of that. One component of resistance on the road will be vibration... which ends up being dissipated and lost. This isn't measured at all on the roller.


Because it bears no relevance to determining rolling resistance.
What you do is add another load at the bottom of the sprung system which is modulated instead of being constant.
As far as rolling resistance is concerned it won't change a thing all else kept equal.

Ciao, ;)

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PostPosted: Wed Mar 12, 2014 9:45 pm 
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Well, then call it tire-dependent system resistance if you will, but to me it sounds logical that isolating the rider (60-90kgs of flesh and bone) from road vibrations can result in higher rolling speed.

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PostPosted: Tue Jul 29, 2014 9:37 am 
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A few months after starting this topic, I finally found chance to try latex tubes by myself.
To be honest, no real difference on my average speed or HR or something else, but they feel better I guess.
A bit softer and, nice lets say.

I also moved UK for some months, so I feel safer about pinch flats on this roads with latex tubes.

I also ride my road bike to work too, and pumping tires up every morning, while you are running late, is really a pain...

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Posted: Tue Jul 29, 2014 9:37 am 


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