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Originally Posted by blue2000s
When you go up in altitude, the ambient pressure decreases, increasing the effective tire pressure.
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Agreed! But, I took the topic here to be centered mainly on temperatures and their effect on the rubber compounds used in Hi-Per or Summer tires.
There is a pressure differential (the pressure difference between inside the tire and out) which changes with altitude. You're talking about guage pressure which measures pressure above/below atmospheric pressure, and this differs with altitude. So it first matters where you filled your tires.
1ATM (standard atmospheric pressure) is 14.7psi -
AT SEA LEVEL. It drops to about 12.2 at 5k' (Denver), and 10.1psi @ 10k'.
So the effect is that your tires become 'over-inflated' as you rise in altitude from
where you filled them because the outside air pressure is not acting as strongly on the outside of the tire with increases in altitude. If you filled them in denver, the tires become 'over-inflated' by 2.1psi@ 10k'. But, if you filled them in miami and go to 10k', the tires will be 'over-inflated' by a much more pronouced 4.6psi. If you live in an area with significant changes in elevation, it's a good idea to know the altitude (above sea level) where you live and presumably fill your tires. Solving this issue is easy... just bring a tire gauge along and release the 'excess' air as you gain altitude, just remember to refill once you hit the lowlands again.