Car Tire Pressure


#1

My cars usually say 29 psi or 30 or 32 psi on the door jambs. The tires say max 35 psi. Whenever my tires are inflated its when I pull in to a Tire place or Jiffy Lube and get them inflated. But my tires are hot then so shouldn’t I inflate them to 35? My understanding is that the number on the door jamb is COLD tires inflated pressure, so if I inflate to 29 or 30 when the tires are in fact HOT, then my tires would be underinflated all the time, thus wasting gas mileage.


#2

The number on the jambs is for cold pressure, yes. If you’re on your way home, and you over-inflate them, you could park it and wait until the next day, then deflate to the proper pressure.

It might be easier if you tested the pressure cold, then drove them until hot, and measured again. It won’t be perfectly accurate, but it’ll be closer than guessing.

The amount of weight the car has (or is carrying) will change the tire’s temperature (and thus inflation), too.


#3

Best thing is to check them with a good gauge first thing in the morning. Then go add air, if they were, say, 4 psi low when you first checked them add 4 psi when you get to the air pump. But don’t exceed the sidewall tire no matter what.


#4

Today, every car owner should own a small air compressor…


#5

what kind of tires do you own that will only hold 35psi? i can’t say I’ve seen any that have been lower than 40 or 44, the highest, 51psi.


#6

I had a set of Michelins that had 35 psi max.


#7

Tires should never be inflated to the maximum rating on the tire sidewall.
Test the pressure in the morning when the tires are cold.
Use a good tire pressure gauge. The pencil types are the least accurate.


#8

texases has the right answer. Measure in the morning to see how many PSI you need and then add that much whether the tires are cold or hot.

If the tires are hot and you didn’t measure them in the morning, then I’d probably go 4 PSI over the cold value to get reasonably close to the right pressure.