effects of lower ambient temperature on tire pressure
 

So we know (according to Tire Rack anyway) that a drop in 10 degree F is worth about 1 psi in our tires. Meaning if I filled up my tires last week when it was 75* to 31 psi, then right now at 35* they should be at around 27 psi.

However, what happens to tire air temp at speed? How does a lower ambient temperature effect the air inside the tires after they're warmed up?

I ask this because if the ambient temp dropped 40 degrees since last week, common sense would say I need to put 4 more psi in the tires today. However, say normal tire temps are about 135 degrees (i'm just making up a number) when the ambient temp is 75. Are normal tire temps still 135? Or are they 95? Or somewhere in between?

'Normal' tire temps will likely be less when it's colder out then when it's hot. If you are at the track though, my experience has been you will ultimately get to the same hot temperature -- it just takes longer to get there.

Boyle's Law does not change. On the track you will heat up the tyres a lot more but on the street you will doubtfully get much of an increase due to driving alone. Pump them up!!
Dirk

Pressure at temperature T (where T is operating temp) is the most important aspect for a tire - not temp, mass or volume, though of course each one is dependent on the others. Since you're supposed to take tire pressures cold, there's a delta-T: operating temps - cold temps. Does that delta-T change with the ambient temperature? Experience says no, but exactly how much does it change?
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