But that's if your running the tire it calls for. what about other tires? For ex. the 37x12.5x16.5, it says 65 psi. You saying not to run it at its rating ether?

 

Exactly, in regards to the handling, load control and stopping performance the vehicle weight and its distribution determine optimum tire pressure not tire size or design. While they play a part in pressure selection there not as vital, as already said you should only run tires rated (speed / ply / load) for your application regardless of size or tread pattern. If you were hauling a heavy load you might increase a bit but otherwise run the specified pressure. You might check out the rubber manufacturers association or take a Napa online course on suspension and steering (I think they may now have a tire and wheel only section). They both offer great information on the subject.

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You should run the load range called for in the door jamb no matter what size tire you run.

 

Well ill be honest i did not know that

 

To find the proper inflation pressure for a tire a different size from what is original on your vehicle:

-Find the original tire size and recommended inflation pressure (usually on driver's door jamb like stated above, but could be somewhere else on the vehicle like inside the gas door)
-Use a good resource (many online, such as tire manufacturers' websites or use Tire Guide) and find your tire size and inflation pressure and correspond them to the load capability of the tire (for your recommended factory inflation pressure, not maximum load)
-Find the new tire size and look at the chart to match the load, and find the corresponding inflation pressure

I don't know if I explained that so people can understand it or not, I'll check back in the morning and edit it if I have to.

I also have access to 2012 Tire Guide as well as many other resources, so if there are any questions what your inflation pressures should be for oversize tires, PM me and I'll help you out.