Thanks for the detailed explanation. René
On Saturday, January 19, 2013, Jan Heine wrote: > The spreadsheet probably is based on Berto's chart, see > > > http://janheine.wordpress.com/2010/10/18/science-and-bicycles-1-tires-and-pressure/ > > > 1) Does tire size (650b, 700c, etc.) affect the optimal pressure for a > give > > tire width? > > No. In any case, the sizes most of us run fall within a relatively > narrow range. 700C is only 10% larger in diameter than 26". > > > 2) If you are a very light person, for wider tires you get some > ridiculous > > low number, like 7lbs. How do you determine the lowest pressure to use in > > these cases? > > All these values are starting points. Frank Berto came up with the > chart based on extrapolation, so the further you go toward the ends, > the less reliable the values become. > > My bike and I together weigh about 200 pounds, and I run my 42 mm > Grand Bois Hetres at 40-45 psi on most surfaces, but closer to 35 psi > on rough gravel. The extremely supple Extra Leger model requires about > 10% higher pressures, since the sidewalls are so flexible. Otherwise, > the tire begins to wash out when cornering on the limit. On the other > hand, you could run a Schwalbe Marathon at much lower pressures, since > the sidewalls are much stiffer. > > > 3) Can I extrapolate these values to tubeless MTB tires as well? > > The chart is based on a 15% tire drop. Mtbs require totally different > pressures - usually much lower. In cyclocross, the rule with tubular > tires (which don't suffer from pinch flats) used to be that you wanted > to bottom out on the rim on the biggest bump that you hit every lap. > If you didn't bottom out, your pressure was higher than optimal for > traction, and if you bottomed out all the time, your pressure was > obviously too low. > > Disclosure: Our sister company Compass Bicycles Ltd. sell Grand Bois > tires and Schwalbe tubes. > > Jan Heine > Editor > Bicycle Quarterly > 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 post to this group, send email to > rbw-owners-bunch@googlegroups.com<javascript:;> > . > To unsubscribe from this group, send email to > rbw-owners-bunch+unsubscr...@googlegroups.com <javascript:;>. > For more options, visit this group at > http://groups.google.com/group/rbw-owners-bunch?hl=en. > > -- Sent from Gmail Mobile -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
