Hi, got an 00 Fx4 lariet, just replaced just replaced tires, a litle confused with the tire pressure. The door jam says 35psi and the tire says 50psi. Which do I go with. I took a BIG hit on the MPG with these tires and I figureed I need to raise the pressure.

 

https://www.f150online.com/forums/sh...d.php?t=281417

This should answer your question.

 

Sure does, thank for your assistance.

 

side wall is a max PSI number. usually tire pressure is set around 2/3% of the max PSI

 

Unfortunately formulas seldom work. 2/3 of max PSI could get you killed if the tire is a P series with a max of 35. That would be 23psi. Ford calls for max on it's P series. LR C tires, Ford calls for 38-40 on an F150. Or 4/5's. A formula that might work for a LR C, will not work for a LR D or E.
That tire with a max psi of 50 could be a LR C or a LR D. Where as before the LR C had a max of 50, LR D had a max of 65, and the LR E had a max of 80, now they have D's with 50 and E's with 65 max. Each tire is going to be a different on an F150.
If the tire listed is a LR C tire then 38-40 would be about perfect and what Ford recommended in the first place.

 

I go by the sticker on the vehicle because usually tires aren't vehicle specific. Meaning that the tire can go on many different vehicles with different weight ratings.

 

That is fine as long as it is the same load range tire. You will find the stickers are different depending upon what load range tire comes stock. On the 04 up, a LR C equipped vehicle will have a recommended pressure of 40. If you put on a set of P series tires with a max pressure of 35, you certainly wouldn't run them at 40. I hope.

 

Wouldn't that information be on the sticker as per manufactures recommendation?

 

Most people from what I have seen do not replace with exactly the same tire. Or load range. If I had a truck that had P series tires on it, the first thing I would do is replace the tires with at least LR C tires. The pressure for a P series is too low to run a LR C on.
I happen to use 2 sets of tires, one for summer and one for winter. They happen to be the same load range, but do not have to be as long as I know what tire pressures to use.