[JASONDHSD]

In the 2010 Manual it says to inflate an extra 1 psi for every 10 degree colder and gives the base line of 32Front/30Rear at 60°F so at 30°F it should be 35/33 but it gives no mention of what to do at hotter temps. If it's 90°F should I under inflate by 3psi?

 

[2.5x_sleeper]

I always check my tire air pressure in the early morning, or in the evening, not really worried about the temperature. If the sun has been heating the tires or you've driven on the tires, it will throw off the pressure (increases it). :wink:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]

 

[crewzer]

In the 2010 Manual it says to inflate an extra 1 psi for every 10 degree colder and gives the base line of 32Front/30Rear at 60°F so at 30°F it should be 35/33...

That's not exactly what the manual says or implies, unless inflation is checked in a garage at, say, 60 F, and then the car is moved outside to an ambient temperature of, say, 30 F.

Ref OM pages 11-31 and -32?

If you inflate the cold tires to the recommended pressure when ambient temperature is 60 F, and the ambient temperature subsequently falls to 30 F, then the tire pressure would drop by ~3 psi (~1 psi per 10 degree F drop), and you'd be looking at adding ~3 psi to each cold tire to bring them back to the original recommended inflation pressure.

However, the instructions are not meant to suggest that cold absolute tire pressure should be inversely adjusted for changes in ambient temperature.

So, no matter what the outside temperature, the factory's recommended pressure specs apply to "cold" tires. Just check 'em in the morning before driving or the Sun hits 'em. Some folks, including me, use higher "cold" pressure to improve handling and/or fuel economy, but that's another matter.

More info here and here.

HTH,
Jim / crewzer