"but altitude can add or subtracts a few PSI pretty easily"
Altitude changes add or subtract from GAUGE pressure, but the actual pressure in the tire doesn't change: same volume _and same temp_\* means same pressure. The tire is still going to offer the same support and conform to the ground in the same way.
Where as temperature changes will effect the actual pressure in the tire. I've heard that an average car tire swings about 1.5 psi for every 10 degrees C. Bikes seem similar: I think I've seen about a 4 psi drop when taking the bike from room temp to just about freezing.
\* (yes, the less outside pressure technically means the tire will try to "inflate" a bit more, increasing the volume and reducing the pressure, but I think that's negligible when we're talking just ~2psi (1000 meters up) vs the tire casing)
\*\* (for now disregarding the temp changes that come with altitude changes, which seems to be about 6.5 C per 1000m)
\*\*\* Lornholio seems to have nailed it.
Feb. 11, 2022, 11 a.m. - Justin White
"but altitude can add or subtracts a few PSI pretty easily" Altitude changes add or subtract from GAUGE pressure, but the actual pressure in the tire doesn't change: same volume _and same temp_\* means same pressure. The tire is still going to offer the same support and conform to the ground in the same way. Where as temperature changes will effect the actual pressure in the tire. I've heard that an average car tire swings about 1.5 psi for every 10 degrees C. Bikes seem similar: I think I've seen about a 4 psi drop when taking the bike from room temp to just about freezing. \* (yes, the less outside pressure technically means the tire will try to "inflate" a bit more, increasing the volume and reducing the pressure, but I think that's negligible when we're talking just ~2psi (1000 meters up) vs the tire casing) \*\* (for now disregarding the temp changes that come with altitude changes, which seems to be about 6.5 C per 1000m) \*\*\* Lornholio seems to have nailed it.