We just tested the tires and recorded the results – I only can offer hypotheses why the tires behave that way. A likely explanation is that the decrease in hysteretic losses becomes smaller once you exceed a certain pressure, but the suspension losses still increase with higher pressures. (You don't get much less flex in the tire, but you still increase the vibrations as you go to higher pressures.) When you look at the original data in Bicycle Quarterly Vol. 11, No. 3, you'll see that different tire models (we tested three different tires in 0.5 bar increments) behave a bit differently, as you'd expect.
As a rider, I don't really care why my tires roll as fast at 50 psi as they do at 100 psi, I am just glad I can get tires that are wide and comfortable, and roll fast. Jan Heine Editor Bicycle Quarterly http://www.bikequarterly.com Follow our blog at http://janheine.wordpress.com/ On Monday, January 6, 2014 4:44:13 PM UTC-8, ted wrote: > > Jan, > Agreed on the practical practice side, but I am still curious about the > med hi to hi pressure phenomena. > If I understand correctly, you say that from nominal to very high > pressure, losses in the tire itself decrease. But from nominal to > moderately high pressures, suspension losses increase more and overwhelm > the reduction in losses in the tire so that the total resistance increases. > However from moderately high to very high pressure total resistance > decreases. Do you have a theory / explanation for that? What component of > the total resistance goes down with increasing pressure in that medium to > very high pressure regime? > Though it's not significant as a practical matter, somehow the engineer in > me still wants to know. > > On Sunday, January 5, 2014 6:50:27 PM UTC-8, Jan Heine wrote: >> >> >> >> On Sunday, January 5, 2014 5:45:23 PM UTC-8, ted wrote: >>> >>> If I read that right, you are saying that your data shows a local maxima >>> at medium-high pressure with lower losses at tire pressures both above and >>> below that point. Is that really what you mean to be saying? >>> >> >> Yes, that is what we found. (There is a second maximum at very low >> pressures, like below 40 psi for a 25 mm tire). As you point out, the >> differences, while statistically significant (we had so much data that it >> was easy to filter out the noise), don't really matter in real life. >> >> "Just ride" really is a good way to think about tire pressure. It's nice >> to know that obsessing about tire pressure doesn't gain you anything. I now >> inflate my Grand Bois Hetres to about 45 psi, and then ride them for a few >> months, until they start washing out under hard cornering, at which point I >> inflate them again. It's nice not to worry about tire pressure more than a >> few times a year. I do reduce the pressure if we are heading over long, >> rough gravel sections, but then I hardly ever re-inflate them even if we >> are riding for hundreds of miles on pavement thereafter. >> >> Jan Heine >> Editor >> Bicycle Quarterly >> www.bikequarterly.com >> >> Follow our blog at www.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.
