Thanks for the information Jan, Some of your comments elicit some questions. You say: "a Grand Bois 700C x 32 mm (or Vittoria CX Corsa 25 mm) tire is as fast at 60 psi as it is at 200 psi. At moderately high pressures (110 psi or so), they actually were a little slower, but this is a minor effect. While statistically significant (so it's not noise in the data), running your tires at 110 psi will only make you marginally slower than running them at 60 or 80 psi."
Are you equating the behavior of high performance 32mm clinchers and 25mm tubulars, or are both tires you mention clinchers? Are you saying these tires have the same rolling resistance or just that their resistances as functions of pressure have the same derivatives, or just that the curves have vaguely similar shapes, or something else entirely? Are you saying that the optimum pressure for such tires from a rolling resistance standpoint is about 60 or 80 psi, and that the variation in rolling resistance anywhere from 60 to 110 psi, though measurable, is negligible? What was the load on the tire for these measurements? Are the rolling resistances at 60, 70, 80, and 90 psi measurably different? If these tires are as fast at 60psi as they are at 200psi (wording that seems to imply equality), but marginally slower at 110psi, doesn't that imply that they are faster at 200psi than at 110psi (though faster still some where between 60 and 80psi)? Isn't that rather surprising/improbable? Are these tires only as fast at 60psi as they are at 200psi or are they faster at 60 than at 200? Have you ever known anybody to actually use a 32mm bike tire at pressures greater than (or even as high as) 110psi? Is it safe to put 200psi in a grand boise 700c 32mm tire? You also say: "... there is a minimum pressure below which rolling resistance increases. In our testing, we found that this pressure was about at the point where the tire no longer cornered safely - pretty low!" Are you saying that for a 32mm tire 60psi is "pretty low!" and that at pressures lower than 60psi cornering is unsafe? You say: "... moderately high pressures (110 psi or so), ...". Do you really feel that 110psi in a 32mm tire is a moderately high pressure? If you do I am going to have to seriously revise my understanding of every qualitative recommendation of yours that I have ever read. I fear I have been seriously mistaken about what "high" and "low" mean. thanks for your help. On Saturday, January 4, 2014 7:26:34 PM UTC-8, Jan Heine wrote: > > Obviously, if your tire is flat, rolling resistance is very high. So there > is a minimum pressure below which rolling resistance increases. In our > testing, we found that this pressure was about at the point where the tire > no longer cornered safely - pretty low! > > There also must be a maximum pressure beyond which tires become slower. At > infinite pressure, the tire would be totally stiff, and then you'd be back > to the old days when wheels were shod with narrow strips of rubber. Those > were very slow. > > In reality, the pressures we tend to ride are in the middle - even 200 psi > isn't making a tire totally stiff - so we don't need to worry about it. > Basically, a Grand Bois 700C x 32 mm (or Vittoria CX Corsa 25 mm) tire is > as fast at 60 psi as it is at 200 psi. At moderately high pressures (110 > psi or so), they actually were a little slower, but this is a minor effect. > While statistically significant (so it's not noise in the data), running > your tires at 110 psi will only make you marginally slower than running > them at 60 or 80 psi. I am quoting from memory, the exact data is in the > *Bicycle > Quarterly* article (Vol. 11, No. 3). > > So for practical purposes, tire pressure should be selected as low as you > can go while still getting good cornering. This holds true at least for > high-performance tires. We haven't tested this for sturdy, belted utility > tires, but if you are concerned about performance, you won't run those, > anyhow. > > Jan Heine > Editor > Bicycle Quarterly > http://www.bikequarterly.com > > Follow our blog at http://janheine.wordpress.com/ > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/groups/opt_out.
