I have grappler 35/12.5/20 tires on my truck with a 6 in lift. I recently had a valve replace and the tech filled the tire to 55 psi. I normally stay around 40 for around town driving. He said 55 psi was where the tires should be. Can someone tell me their thoughts on correct psi?
Cheers

 

Methinks the "tech" has no clue. The door placard will show you what pressure to use. 55 psi may be well over the max inflation pressure.

 

Check the door sticker. What's stamped on the tire is max pressure.

 

The door sticker only applies if the tires are the same as factory. IE plies, load rating. I have 305/70/17 terra grapples, door says 60 front40 rear (light load). I run 40 in the rear 50 up front. Tires have a higher load rating than what can on the truck.

 

Door says 35 psi tire max is 65. But these are not stock tires

 

I have the terra grapplers on mine and run 40 p.s.i. its just enough that it's not squishy feeling but not to rough either

 

Best bet with oversize tires, is to do the 'Chalk Test'

Load your rig as it will be loaded most of the time, then take plain white chalk, and make a few lines across the tread, on all 4 tires.

Drive on clean blacktop (I use parking lots ) for about 100 yards, and see how the chalk wears.

May take a few tries, but once you get the chalk to wear off evenly, you then know the tire pressure.

Make a note of the front and rear, and then run them at that pressure.

(If you have an AWD pressure should be equal all around)

This method will give you the longest life for your tires, especially mud terrain.

My new to me '09 with Good Year Duratracs likes 45 front and 43 rear, close enough to run 45 all around.

My '00 Jeep TJ with 35x12.5-15 Cooper STMaxx's likes 25psi.

Seems low, but the Jeep is lighter than a truck, and after 4K miles I have nice even tread wear, and no problems on the street with sidewall roll.


This method works best with new tires.