On Jan 5, 2014, at 12:42 PM, ted <[email protected]> wrote: > Does anybody else remember Jobst asserting back in the early 90s that > tubulars were slower than clinchers because of the glue? I think the "... > flattening was more pronounced in tubulars than clinchers." that Tim mentions > was part of his reasoning.
Back in rec.bicycles.tech years ago, Jobst noted the different shape of the curve for tubulars and came to the conclusion that the tubulars were squirming on the glue bed, road tubular glue being somewhat soft to allow the tire to be removed and put back on or replaced without having to put more glue on the rim. Track riders long used shellac to adhere the tubular to the rim, which forms a hard bond with no flex; once the tire is removed (with difficulty) new shellac has to be applied to glue the new tire on the rim; Jobst thought that a hard glue like shellac would eliminate the losses and that tubulars would then show the same curve. I don’t know if that was tested. FWIW, IIRC the Avocet tire tests were done with an asphalt covered drum instead of a smooth steel drum. IIRC Jobst also did slip angle tests by riding on an asphalt covered wood platform, finding that bike tires slip out at a 45 degree angle to the ground. I wonder if there is a difference in the slip angle based on tire width and/or inflation pressure. Racing motorcycles appear at times to get below 45 degrees, although as I am looking at head-on photos of cornering racing motorcycles that may be an illusion of camera angle. I have been reading Jan’s book on Rene Herse, which my wife gave me for Christmas. There is a great photo (one among many) of a tandem (Prestat/Herse, I think) rounding a downhill corner with another immediately behind. While they do not appear to be at the cornering limit, the bike is on the inside of the turn on rough and perhaps gravelly pavement and yet appears quite sure footed- at least the riders don’t look at all alarmed. It appears to have 650B x 42 tires or thereabouts. I have felt that wider, softer tires seem more secure in corners (although consistent with my earlier posts I don’t know if that is actually true versus an assumption) than skinny hard tires. I had a demonstration of this back in my track racing days when I punctured my front wheel (track tubular at 110 psi, maybe 20-21 mm wide) and borrowed a front wheel from another competitor. His wheel had a 700 x 19 or so Continental Grand Prix pumped up to 140 psi or something like that. It felt incredibly unstable, like it was on ball bearings so there was no resistance to the handlebar swinging back and forth, really quite unsettling although it didn’t slip or do anything untoward on the boards. I was glad to give him his wheel back at the end of the night. -- 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]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/groups/opt_out.
