joshatsilca wrote:
So the bead width changes the effective tire width and height. A 25mm GP4000s on a 13mm bead width rim (the old standard) measures at 25.6mm wide and on a 17mm bead width (common new carbon wheels) it measures at 27.1mm wide and on something very wide like an ENVE 7.8 with 19.5mm bead width, that same tire measures, 28mm wide at 100psi! Effectively, the tire is able to act as a larger diameter than listed on the casing as the bead widens.
J
Josh so the pieces you provided for the "Tire Pressure - Stop Guessing" article are interesting. We had this discussion earlier this spring when I was looking for a recommendation for my pro female roommate riding wider rim Enve wheels. I wish we could get a "Ask Josh at Silca" thread going about this so it isn't buried in this thread. Looking at your main graph, not sure if you provided this to Jim Gourley or not but can you give any more specifics to the testing?
It appears, that a 25mm Conti was used, but does not indicate at which speed you were rolling the rubber, the weight of the rider + bike, nor the wheel and it's internal diameter. Recently I had the chance to test out some HED Jet+ which are 21mm wide. This is opposed to my old Zipps that were 16.25mm wide. I did some "quick" tire pressure testing, just finding the number of pumps it took to get my previous tire pressure on the Zipps, then repeating this on the HED Jet+ and stopping at the same number of pumps and recording the PSI difference. I tested many tires, many runs, but in the end it seemed like same number of pumps (#22 pumps fwwiw Joe Blow Sport) results in 9psi lower on the HED Jet+ than the Zipp. My baseline was a Supersonic 23mm that I was pumping to 100psi. Through this testing it also reinforced just how much tires grows thru use as I was seeing a 5% difference in psi between new and old tires.
My question is what is the optimal pressure. Given a 152 lbs + 18 lbs bike for 170lbs total. Using HED Jet+ with 23mm (narrow 23mm) what is the optimal PSI.
Btw, my approach from here on out since I rotate new SS on to the front, and then once used for a few races to the back, is that both PSI, front and rear, will be the same. Fwiw, I rode 94 PSI at Raleigh assuming a few PSI leak for the latex. I pumped at 82 two weeks ago at Chattanooga.
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