nothing really crazy here, but it did peak my curiosity.
Does anyone consciously think about the fact that the race is hot and on black asphalt and thus reduce their tire pressures?
I am about 137 on race day riding 23mm clincher 4000s with latex tubes. I usually put them around 95 psi for race day (that is what all those neat charts show).
I would imagine that there would be a slight increase in pressure due to heat, but over 5 or so hours on the course, there is also a decent amount of leakage from the latex.
Obviously not a critical deal, just something that got me thinking.
For every 10 degree rise in temp, air pressure in a tire rises 2 PSI. Not sure how hot the tire gets on the Queen K. Let’s assume it 75 in the morning when you pump and its 105 on Queen K at noon. Based on on what I read, you could get a 6PSI rise in pressure.
For every 10 degree rise in temp, air pressure in a tire rises 2 PSI. Not sure how hot the tire gets on the Queen K. Let’s assume it 75 in the morning when you pump and its 105 on Queen K at noon. Based on on what I read, you could get a 6PSI rise in pressure.
So if you use latex tubes you can just sorta ignore the issue!
For every 10 degree rise in temp, air pressure in a tire rises 2 PSI. Not sure how hot the tire gets on the Queen K. Let’s assume it 75 in the morning when you pump and its 105 on Queen K at noon. Based on on what I read, you could get a 6PSI rise in pressure.
pv=nRT is the way to go.
However, one important thing. We don’t care so much about the rise in ambient air temp. We care about the air temp in the tires. A black tire on black asphalt in the direct sun in HI in October? I would wager that it is gonna be a pretty significant rise of temp in there by hour 4 of the bike.
Guy Lussac’s law of constant volume, pressure and temp. Just tell me how hot a tire gets on the Queen K and maybe we can come to some agreement on how much the PSI would increase.
Well, only part of the tire.
Because part of the tire has an airspeed of exactly zero.
And the heat load of infrared radiation is considerable. Just think about how you feel riding in 100 degrees, but in direct sun. Unless you’re wearing aluminum foil, you feel like it’s 140 plus, even with all that ‘cooling’ air. Now pretend you’re wearing an-all black rubber suit, kinda like a tire. Ouch.
If only there was a simple equation to help us think about this question!
pv=nRT
Air is compressible, and thus, does not follow the ideal gas law (even more so in Hawaii with the high humidity). It’s a pretty good estimate for relatively small changes, though.