The derivate of contact patch area with respect to "drop". I think the support force is roughly psi times contact patch area. I think that though the internal pressure may increase slightly that effect is negligible because the change in tire volume is a tiny fraction of the total. I think the spring rate is psi times delta area divided by delta drop. I think the relationships between contact patch area, tire width and drop are a bit complicated. I suspect spring rate dependence on width is closer to linear than the width squared dependence that is implied by assuming it varies with cross sectional area (which is what I think you are suggesting). So for cush I think it is closer to a linear linear dependence.
For pinch flats I think you get a linear increase in spring rate from the width and another linear increase in allowable deformation due to the hight that goes with the width. So that would suggest a scale factor squared dependance on that front. My experience of late has been that I pick the pressure based on ride and handling. Pinch flats just haven't been a problem for me. Of course I don't assume that is the case for everybody. On Tuesday, June 10, 2014 7:14:42 PM UTC-7, Anne Paulson wrote: > > The effective spring rate is going to depend on volume, isn't it, because > the volume says how much air there is and that determines how much > compression there can be? And the contact patch is going to depend on > diameter, isn't it? > > The derivative of the contact patch with respect to what? > > > On Tue, Jun 10, 2014 at 6:34 PM, ted <ted....@comcast.net <javascript:>> > wrote: > >> I would think we care about effective spring rate (cush) and how much >> additional travel is possible before getting a pinch flat. Aren't those >> driven by the contact patch size, its derivative, and the height of the >> tire? How does cross section area (or volume) drive those? >> Are you sure this is a diameter squared dependency? >> >> On Tuesday, June 10, 2014 5:31:44 PM UTC-7, Anne Paulson wrote: >> >>> It's 6% in diameter, but that makes 12% difference in volume, which is >>> what we care about. >>> >>> >>> On Tue, Jun 10, 2014 at 4:56 PM, Deacon Patrick <lamon...@mac.com> >>> wrote: >>> >>>> That's about a 6% discrepancy, which certainly seems reasonable given >>>> different rim widths and tire stretch. >>>> >>>> With abandon, >>>> Patrick >>>> >>>> >>>> On Tuesday, June 10, 2014 4:52:31 PM UTC-6, Anne Paulson wrote: >>>>> >>>>> If you order some of Jan Heine's tires, be aware of a size discrepancy. >>>>> >>>>> I just got a couple of his Grand Bois tires, which are sold as 700 x >>>>> 32mm. I knew they were made by Panaracer, and I have used the Panaracer >>>>> Pasela 32mm and the Jack Brown 33mm tires, so I figured I knew what to >>>>> expect. When the tires arrived, they looked narrower than I expected. >>>>> Then, >>>>> when I opened them up, they were labelled 700 x 30. Then, when I mounted >>>>> them on my Mavic Open Pro rims, they measured 30mm wide. >>>>> >>>>> When I asked Jan, he explained that he has a different system of >>>>> measurement, and according to his measurement system (mounting them on >>>>> some >>>>> rim or other) they measure 32mm. >>>>> >>>>> So, expect the Grand Bois tires to be narrower than other tires sold >>>>> with the same width. >>>>> >>>>> -- >>>>> -- Anne "Standards are good, everyone should have one" Paulson >>>>> >>>>> It isn't a contest. Enjoy the ride. >>>>> >>>> -- >>>> 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-bun...@googlegroups.com. >>>> To post to this group, send email to rbw-owne...@googlegroups.com. >>>> >>>> Visit this group at http://groups.google.com/group/rbw-owners-bunch. >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> >>> >>> -- >>> -- Anne Paulson >>> >>> It isn't a contest. Enjoy the ride. >>> >> -- >> 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-bun...@googlegroups.com <javascript:>. >> To post to this group, send email to rbw-owne...@googlegroups.com >> <javascript:>. >> Visit this group at http://groups.google.com/group/rbw-owners-bunch. >> For more options, visit https://groups.google.com/d/optout. >> > > > > -- > -- Anne Paulson > > It isn't a contest. Enjoy the ride. > -- 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/d/optout.
