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PostPosted: Tue Dec 11, 2012 6:42 pm 
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Joined: Tue May 03, 2005 2:20 am
Posts: 5746
Location: Belgium
Hi,

Quote:
Testing on a steel drum may be more accurate and reproducible, but it has little, if any, relationship to real world use.


If we agree that we're testing roling resistance and nothing else then let me tell you with 100% absolute certainty that there is 100% correlation between the results as found in the lab and in the real world.

IOW a tyre that does not show good rolling resistance figures in the lab won't roll well in the real world either and vice versa.

I personally do not object to the methodology used in that test it's just that some of the conclusions they draw from the outcome are completely off the wall.

Anyway, pls reread my previous post and maybe you'll understand it better.

Quote:
I'd suggest that you read the actual papers before passing judgement. Although I disagree with a significant amount of what I read in Bicycle Quarterly, Jan and his fellow testers deserve to be commended for actually attempting to do an analysis that approximates actual riding conditions.


Papers, what papers?
All it does is confirm (once more) what every engineer (and everyone with a bit of common sense for that matter) already knows for at least a century.
I'd be happy with that if it were not that they just had to add some complete nonsense which does nothing for their credibility, quite the opposite.

Ciao, ;)

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PostPosted: Tue Dec 11, 2012 6:49 pm 
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Posts: 224
WMW wrote:
fdegrove wrote:
Carrying out such tests is far more easy to do and far more precise in a controlled environment.
From that prespective the lab tests as carried out by Tour magazine are scientifically far more valid than any such test carried out on a road.


That "road" test simply has too many confounding variables... wind being a huge one, plus body position, different wheels, etc. These are easily great enough to swamp any Crr numbers.


Agreed. But did you read the study to see how they controlled for these variables, or are you just hypothesizing? Take the time to read the study and then make up your mind, but don't comment on something you haven't read.

The problem here is that people prefer to rely on anecdotal evidence rather than the best available data. Are there flaws in BQ's methodology? Sure. But it is the best analysis we have right now of the relationship between real-world riding conditions and tire brand, width, and pressure.

And the funny thing is all these tests were done years ago, but nobody paid attention to the benefits of wider tires until Specialized contracted out a study that basically confirmed the results of the BQ analysis.

Anyway, all of this has been argued ad infinitum on various internet boards, in some cases for years. If people prefer to rely on anecdote over evidence, more power to them!

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Posted: Tue Dec 11, 2012 6:49 pm 


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PostPosted: Tue Dec 11, 2012 6:58 pm 
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Posts: 224
fdegrove wrote:
Hi,
If we agree that we're testing roling resistance and nothing else then let me tell you with 100% absolute certainty that there is 100% correlation between the results as found in the lab and in the real world.

IOW a tyre that does not show good rolling resistance figures in the lab won't roll well in the real world either and vice versa.

Quote:
Although I disagree with a significant amount of what I read in Bicycle Quarterly, Jan and his fellow testers deserve to be commended for actually attempting to do an analysis that approximates actual riding conditions.


Papers, what papers?
All it does is confirm (once more) what every engineer (and everyone with a bit of common sense for that matter) already knows for at least a century.
I'd be happy with that if it were not that they just had to add some complete nonsense which does nothing for their credibility, quite the opposite.

Ciao, ;)


There is only a moderate correlation between rolling resistance results as found in the lab and in the real world, contrary to what you've said. Drum tests may be relevant for track racers, but not for anyone who rides on an actual road.

And regarding the papers, several studies were published in Bicycle Quarterly, which isn't a peer reviewed journal but they do provide detailed information on their methodology and results.

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Last edited by xrs2 on Wed Dec 26, 2012 9:28 pm, edited 1 time in total.

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PostPosted: Tue Dec 11, 2012 8:18 pm 
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Tubbie Guru

Joined: Tue May 03, 2005 2:20 am
Posts: 5746
Location: Belgium
Hi,

Obviously you do not seem to get it:

Quote:
Whether or not the tyre sees a fixed load (brick of lead fror instance) or a rider + a road as load isn't relevant at all for measuring rolling resistance either for as long as the load is the same for all devices under test. Something you can't be sure of when testing outdoors on a strip of road.
Point is that the relative order of difference between the test participants should and will be absolutely the same in both tests. The absolute figures may differ yet the differences should remain.


Quote:
Read them instead of relying on second-hand accounts from the internet and then we'll talk.


Maybe if you had you would not need to retort with such poor arguments?

Read this first as well while you're at it:

http://en.wikipedia.org/wiki/Rolling_resistance

Ciao, ;)

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PostPosted: Tue Dec 11, 2012 9:02 pm 
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Joined: Mon Nov 07, 2011 5:46 am
Posts: 224
fdegrove wrote:
Hi,

Obviously you do not seem to get it:

Quote:
Whether or not the tyre sees a fixed load (brick of lead fror instance) or a rider + a road as load isn't relevant at all for measuring rolling resistance either for as long as the load is the same for all devices under test. Something you can't be sure of when testing outdoors on a strip of road.
Point is that the relative order of difference between the test participants should and will be absolutely the same in both tests. The absolute figures may differ yet the differences should remain.


Quote:
Read them instead of relying on second-hand accounts from the internet and then we'll talk.


Maybe if you had you would not need to retort with such poor arguments?

Read this first as well while you're at it:

http://en.wikipedia.org/wiki/Rolling_resistance

Ciao, ;)


We are clearly not arguing about the same thing. Perhaps take a moment to consider whether your argument is even remotely related to the issue at hand. In any case, this has been rehashed thousands of times elsewhere. Please do take a moment to read the studies. Wikipedia is not a valid source.

The last word is yours.

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PostPosted: Tue Dec 11, 2012 9:26 pm 
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Tubbie Guru

Joined: Tue May 03, 2005 2:20 am
Posts: 5746
Location: Belgium
Hi,

Quote:
We are clearly not arguing about the same thing. Perhaps take a moment to consider whether your argument is even remotely related to the issue at hand. In any case, this has been rehashed thousands of times elsewhere. Please do take a moment to read the studies. Wikipedia is not a valid source.


I see. Someone must be moving the goalposts then?

So, in a nutshell: rolling resistance has been redefined since I last went to college, I read studies but clearly not the right ones and Wikipedia is not a valid source even when all it takes is a simple law of physics.

Excuse me for trying to mingle with brighter minds than my own..... :oops:

Now if you would be so kind to let the rest of the world know what you are talking about, what it is that has been rehashed a thousand times before and what on earth "the studies" are, we'd all be much obliged.

Thank you for posting, ;)

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PostPosted: Tue Dec 11, 2012 10:12 pm 
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The argument made by Heine against roller testing is that dissipation in the rider (by transmitted vibrations) is an important component of rolling resistance (an energy dissipation term proportional to speed and roughly proportional to weight). Therefore roller tests would tend to over-estimate optimal tire pressure, since a cost of high pressures, which is increased damping in vibrating the rider, would be neglected.

By shifting the preference to lower pressure, that shifts the preference to wider, thinner tires.

This has been debated on BikeTechReview's forum.

A curious conclusion reached by Bicycle Quarterly is that latex tubes are slower. But I suspect this was an artifact of their particular choice of tubes. Al Morrison @ BikeTechReview clearly shows better results from latex.

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PostPosted: Wed Dec 12, 2012 12:31 am 
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Tubbie Guru

Joined: Tue May 03, 2005 2:20 am
Posts: 5746
Location: Belgium
Hi,

Quote:
The argument made by Heine against roller testing is that dissipation in the rider (by transmitted vibrations) is an important component of rolling resistance (an energy dissipation term proportional to speed and roughly proportional to weight). Therefore roller tests would tend to over-estimate optimal tire pressure, since a cost of high pressures, which is increased damping in vibrating the rider, would be neglected.


If that is true it has nothing to do with the rolling resistance of the tyre as such but everything with the rolling resistance of a bicycle, his rider, his wheels and the damping factors of all of these combined.
Therefore the measured rolling resistance will vary with the impact of any of the above factors and it will change continously whilst moving from one piece of road to the next. Hell even the airpressure level surrounding the rider will effect the rolling resistance.

Now tell us, should we cover our bikes in sorbothane? Should we lose or gain weigth? Should we use saddles with or without padding? Back to steel or titanium frame?

I could be wrong but IMO the bulk (as in 95% or more) of the dissipation of energy is happening at the suspension end of the bicycle, IOW the tyres.
So, and I say this with respect, if mr. Heine wasn't measuring tyre rolling resistance but rolling resistance in general he should not have stopped at just measuring tyre rolling resistance either, wouldn't you agree?

I think they also forgot to measure the rolling resistance of the road they did the testing on as that too is a variable which can vary against yet another pile of variables as well....

For clarity's sake, I'll repeat it once again, Crr, in casu tyre rolling resistance, is a relative value allowing you to compare what can reasonably be compared. IOW it will allow you to create a picking order of preference from the testresults.
A tyre with a low rolling resistance relative to another tyre tested on a drum, in a lab, at a constant speed, constant load, is going to keep this low rolling resistance relative to that other tyre no matter what testing protocol you throw at it unless you bias that protocol to favour one outcome over the other. E.g. wildly overinflate, underflate, whatever.

Throwing in a road (which is only going to modulate reaction force R) and replacing W, a dead weight serving as a constant load, by a highly absorbant mass such as a human body, is not going to change the relative rolling resistance of one tyre to another.
Anything else, as described above, has nothing to do with rolling resistance but has everything to do with trackability.
Much in the same way a phonograph cartridge can track a groove thanks to its (electrical) load and suspension if you like.
In a similar vein a bicycle frame, wheel, you name it, can be optimised by applying well understood physics. Vertical compliance, choice of layups, variable wall thickness, pipe shapes, asymetry, etc. etc. can all be varied to obtain a particular sought after result.

The list is endless but to give one example: the current reversion to the old 27.2mm standard for seatposts because it is perceived as being more comfortable is not a mere incident. It is just applied physics nothing more, nothing less.
It too contributes to making a bike "roll" better.....

Ciao, ;)

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Last edited by fdegrove on Wed Dec 12, 2012 1:52 am, edited 1 time in total.

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PostPosted: Wed Dec 12, 2012 1:45 am 
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Joined: Sun Jul 29, 2012 2:59 pm
Posts: 505
Location: Ruidoso, NM
djconnel wrote:
Therefore roller tests would tend to over-estimate optimal tire pressure, since a cost of high pressures


No one uses roller tests to determine optimal tire pressure.

Quote:
A curious conclusion reached by Bicycle Quarterly is that latex tubes are slower. But I suspect this was an artifact of their particular choice of tubes. Al Morrison @ BikeTechReview clearly shows better results from latex.


Every real test shows latex is better. BQ's different result is due to a poor test protocol.

5 years ago I analyzed BQ's test and determined that a 1 mph difference in wind was equivalent to changing Crr by ~.004... which is the total Crr for a good tire! In other words we are looking at +-100% error for 1 mph wind!. And there are a bunch of other errors to boot.

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