Just don't hold your breath. On Tuesday, January 7, 2014 9:48:36 PM UTC-8, Christopher Chen wrote: > > I look forward to your results, Ted. > On Jan 7, 2014 9:42 PM, "ted" <[email protected] <javascript:>> wrote: > >> I don't see how this relates to my question. >> I think it is a possible (or even probable) explanation for resistance >> increasing as pressure increases from nominal to moderately high values. >> My question is what could explain resistance then decreasing as pressure >> continues to increase from moderately high to very high levels? >> I think the hypothesis you present is inconsistent with that aspect of >> your experiments results. >> As the tire gets harder wouldn't the suspension losses continue to >> increase? Aren't the reductions in losses in the tire itself likely to >> continue to become smaller and smaller, or even reverse? What can possibly >> explain resistance decreasing as tire pressure increases from 140 to 200 >> psi if resistance had already gone through a local minimum below 140 psi? >> >> Of course you are quite right that this is of no importance when we go >> ride our bikes, but when experimental data seems to contradict our >> understanding of how something works I like to find at least a possible >> explanation. Don't you? >> >> On Tuesday, January 7, 2014 11:18:30 AM UTC-8, Jan Heine wrote: >>> >>> 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 [email protected] <javascript:>. >> To post to this group, send email to >> [email protected]<javascript:> >> . >> Visit this group at http://groups.google.com/group/rbw-owners-bunch. >> For more options, visit https://groups.google.com/groups/opt_out. >> >
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