Warbird wrote:
longtrousers wrote:
Warbird wrote:
longtrousers wrote:
5 bars seems to be very low to me, but probably I have to learn and go even lower than the 100 psi I run at the moment.
I'm a bit confused at the moment.
I might try to run 6 bars with conti 5000, I weigh 190 lbs; do you think that would be ok? I would fear flats, especially in a race I rather loose some speed as getting a flat.
I weigh a bit more than you (215 at the moment, have been heavier over the last few years), I haven't run anything above 95psi in years. I can't remember the last time I had a pinch flat. With 23mm GP4Ks (which measure 26mm on my wheels) I'm running around 90psi, and with 25mm GP4Ks (which measure 28mm) I'm running around 80psi. If I were 190 lbs, and/or my tires measured wider, I'd be running even lower pressures...
I remember a snake bite when I had a bit lower pressure, anyway I have 23 mm front and 25 rear and as I said I pump up to 100 psi at the moment. You have 80 psi. Isn't it strange that zipp restricts such:
"The 303 Firecrest has a max tire pressure of 72.5psi (5 bars)"
I mean at least me but even you as a rather low pressure rider could not purchase this rim because you can only inflate it up to 72.5. I think, but correct me if I'm wrong, that also Tom A and Josh at Silca talk about pressures of 100 psi on rough roads. Although lower pressures are even faster but more prone to flats. This max of 72.5 psi just feels strange to me as if it is a typing mistake.
Actually, I could run the recommended pressure, I would just need a tire that measured at least 30mm when installed on those rims. With a 30mm tire, I would be right at the recommended maximum pressure, with 32mm tires I could run in the mid 60s.
How wide are your rims, and how wide do your tires measure when installed on them? If I put a 23mm tire on my old Open Pros, on average the tire is actually going to measure 23mm, and according to Silca's calculator (and my own testing), my ideal pressure would be about 110psi. Put those same tires on my FLO 60s, and now the tire measures 26mm. And according to Silca (and again, my own testing), low 90s is ideal, while 110psi is noticeably slower and harsher riding. Put 25mm tires on the FLOs, and they now measure 28mm, and the ideal pressure drops again to about 80psi. And 110psi rides like crap.
Also keep in mind that tire widths are very inconsistent across brands. I've seen a lot of OEM spec tires that run significantly narrower than labeled, even on wider rims...
Thanks for your thoughts. I looked at Silca tire pressure calculator, but that only seems to work in the "professional" version.
Anyway, I measured my sizes:
Front Tire: 23mm 4000 SII measures 24,2 mm Rim: 808FC 27mm running 7 bar 100 psi at the moment
Rear Tire: 25mm 5000 measures 26 mm Rim: Citec 24 mm running 7 bar 100 psi at the moment
In races I run 25mm 5000 on the front, that should aerodynamically still be ok, staying under 27mm of the rim.
Aerodynamically, the rear tire seems to broad for the narrow citec but I think that does not matter because the rear wheel is hidden anyway on the front by the frame. I weigh 85 kg (187 lbs).
Last edited by:
longtrousers: Jul 12, 20 1:28