Latex Tubes vs Ultra Light Butyl Tubes?

[WMW]

WMW: if you could share how you come to that conclusion (edit: re Heine's testing), that would be great. It seems people are either strongly following, or rejecting Jan Heine's work, but I've never seen the critique being substantiated beyond "one doesn't test like that". I'm an engineer myself, but not in a mechanical field, and interested to understand the issues at hand better.

Jan did coast down tests on a full bicycle... on different days. Anyone who has looked at the physics knows that aero drag dominates the test he did, and slight changes in wind or position will swamp the small differences between tubes... or tires for that matter.

[WMW]

The tube didn't make a sound when it went flat and it wasn't pinched in the bead.

Then what was that "pow" you mentioned and why did the tire come off?

Like I said, a properly installed tube has very little stress. Zipp tested latex tubes and found that the rim strip would melt and fail before the tube had an issue from heat.

[rmerka]

Tire didn't come off, poor choice of words in the first post. Also the rim is 202 carbon clincher and the rim strip didn't melt. I think I still have the tube. I'll post a pic of the burn if I can find it.

[dunbar42]

Jan did coast down tests on a full bicycle... on different days. Anyone who has looked at the physics knows that aero drag dominates the test he did, and slight changes in wind or position will swamp the small differences between tubes... or tires for that matter.

You can read about the test at the link below. 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.



http://janheine.wordpress.com/2012/06/1 ... -of-tires/

[weightLight]

Butyl condoms and Latex tubes, oh shit, or is it latex condoms and butyl tubes, oh man I can never remember!

[HillRPete]

dunbar42: my gut feeling would be along those lines too, but again, I'm not an expert. Having only read the online material, not print, I think they have been making an effort in working out which of their results carry statistic significance.

On a steel drum, a steel wheel will have the lowest rolling resistance, resembling a railroad setup. But on the road or rougher surface, a steel wheel will not roll the best (apart from traction issues). Dunlop figured this out for us.

But anyway, I'm looking forward to try bigger tubulars with latex tubes this spring.

[Marin]

I'm getting the feeling that a little bit of damping (i.e. hysteresis) in the tire might actually be a good thing in the real world (as opposed to lab tests on smooth surfaces without a rider) since it will reduce the transfer of vibrations to the rider by reducing the spring-back of the tire and thus transferring less energy to the rider's mass.

[gospastic]

I read this interview the other day with Josh Poertner, former Zipp employee. He seems to believe in latex tubes. Good enough for me.

http://nyvelocity.com/content/interview ... h-poertner

[HillRPete]

Jan did coast down tests on a full bicycle... on different days. Anyone who has looked at the physics knows that aero drag dominates the test he did, and slight changes in wind or position will swamp the small differences between tubes... or tires for that matter.

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.

[LouisN]

I'm trying to find some decent light tubes to buy as a batch (for the kids's clincher wheels, and spare tubes).

But unfortunately, I only had bad luck with ultra light butyl tubes.
Mostly Vittoria and Michelin.
They seem to be even more prone to flats than latex.

Any recommendation for an ultralight butyl tube that served you well ?


Louis

[Zigmeister]

There is an obvious quality difference between latex as well. I used to ride Vittoria Corsa Evo CX 23c tubulars. By the next morning, nearly flat after a ride.

Became really disenchanted and disappointed in Vittoria.. The quality, finish, valve area, real garbage lately. Once I got a hold of some Veloflex Carbon tubulars...yes, a step above IMO.

Those will hold air for days, never really go flat at all between rides. So there is something different going on with those compared to the Vittoria latex tubes. Valve holes were all sealed/plumber tape real well, so it wasn't leaking from there at all.

Currently riding a Conti Force rear tubular, 24mm butyl, Veloflex Carbon 23c front/latex. The ride is pretty much the same until you drop the pressure to 90psi. 95-100psi+, the ride is very similar between the two. They are mounted to 56mm wide/tubular carbon rims strung up tight.

Hope I get an extra 5watts out of the Veloflex though, I need it during a race.

[fdegrove]

Hi,

They seem to be even more prone to flats than latex.

That's perfectly logical as butyl does not have (by nature) the extremely high stretch factor of latex (especially natural, unpigmented latex) so it can not conform around an object the way latex can. Hence the add anti-puncture advantage of latex over butyl.

Just as WMV, I too am rather sceptical of the ability of thin butyl tubes to have lower RR than latex. Seems highly unlikely given the above.

I've never seen latex burn. Seen stretch marks and signs of overheating. If you do spot this then replace the tube immediately.
Latex is impossible to manufacture uniformly so don't pump it up (over half a bar say) outside its envelope as you'll likely damage it.

Correct me if I'm wrong but isn't latex about 90 times more flexible than butyl?

Ciao,

[WMW]

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.

[WMW]

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.

[HillRPete]

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.