New JP Magazine has an article reviewing several different tires. One thing I noticed is that they seemed to run low pressures, 28-32 psi, for on road use, often with lower pressure in the rear. I am running GY MTRs, 35x12.5x17, with about the recomended 35 psi all the way around. Am I missing something?

 

I run 33 12.5 17s Mud Countrys an i like them at 40psi on road. So far wear is even at 18k.

 

Maybe. How wide are your wheels? With my 8" wheels the edges of my 315's weren't touching the pavement at 30 PSI.

Typically, we use wheels that are too narrow for best onroad use. Low pressures and the associated disadvantages are what we pay for not popping a bead at even lower pressures off road.
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There are some guidelines in the FAQ's stickied to the top of this modified area.

But yes, 28-32 is very common for 35" tires. Do a chalk test and see what you come up with.

 

What he said...

 

I noticed my gas mileage go from 16MPG @ 24lbs. to 21MPG @ 34lbs. Stock Sahara 18" wheels with stock tires.

 

What is a chalk test?

 

Higher psi has you running on the center of the tread, which means less tire contacting the ground. It also means you will wear the tires out quicker, right down the middle. Do some math to see if the fuel savings outweigh a new set of tires.

 

The "Chalk Line Test": Draw a heavy chalk line across all the tread faces. drive slowly forward in a straight line for a few revolutions of the tire. Get out and observe the wear pattern of the chalk. If it has worn away evenly, then the inflation is correct. If either the edge or center of the line is worn first, then the tire is under or over inflated, respectively.