fishbones182

Just put federal Mt tires on the truck. They are 35/12.5/20lt. Guy at the tire shop says to run them at the psi on the door jamb.. Max psi is 65 on the sidewall. I'm thinking 35 isn't enough. What do you guys run to get the best wear out of them. Load range d on 12 fx4 crew.

DBL Boost

Run what's imprinted on the tire 65psi

rplatt2189

I've got same size and I run 46 psi

Lethal Weapon

Do NOT run the max shown on the sidewall. That is the maximum pressure those tires should have with the load rating displayed beside it. (Ex: pulling a large trailer, TT, heavy loads, etc).
That info is only telling you the MOST air pressure each tire is safely rated to handle.
If you put too much pressure in the tires, they will be overinflated and will be running on the center of the tread & not evenly across. (Under inflated will run in the outside & inside of thread more than the center).
To answer: approx 32-35 psi is fine to run.
Technically you should have a little more in the front due to the extra weight of the motor.

vozaday

Like what lethal said, several companies have pressure conversions for going from P tires to LT or mud of different sizes online. It usually works out to about 3-5psi above the door jam pressure.

11screw50

Don't run them at max but dont run them at the pressure on the door jamb either. 65psi means they are load range D. An LT tire can carry less weight than an P-rated tire at 40psi (but can be aired to a higher pressure and can carry more at that higher pressure).

I run my LR 'E' tires at 50-53psi as that is what pressure is needed to carry the max that the truck is rated to carry. I suspect with 'D' tires you're probably looking at 45-48psi as a correct pressure (but it really does depend on the tire).

As a rule of thumb, the weight carrying capacity is about the same percentage of max as the pressure to max pressure percentage so if the tire can carry 3500# at 65 psi, it would be ~1750# at 32psi (and those factory P rated tires are generally around 2400# max at 40 psi). your axle rating is 4800# or less so 2400# per tire max is what you need to be able to carry. Keep in mind, this will get you close but it won't be exact.

Or you could do a chalk test and use that. If you air them up to max, you will wear the centers out first.

Lethal Weapon

The chalk test does work quite well.... Make sure the tires have already been warmed up for a couple miles & go somewhere like a school empty parking lot that has a smooth asphalt finish. That works quite well!

gDMJoe

• as long as the door sticker recommended PSI is for LT tires you can use that.
  .
• the sidewall MAX(imum) PSI is just that ... The maximum PSI when the tire/vehicle is loaded to its capacity. *NOT to be used as a regular use PSI.
  .
• ROT (Rule Of Thumb) when unknown ... 75% - 80% of the sidewall MAX and monitor thread wear.

fishbones182

Thank you for the ideas and suggestions. I'll probably air them up to about 43psi and see what happens. Just looking to get the best tread wear out of them that I can.