I just went from running 265/70/R17's to 37/12.5/16.5's. I noticed that my oil pressure is slightly higher now. Is that because of the extra load on the truck to turn the bigger tires or what. After i drive for a little ways (5 miles) the oil pressure seems to get closer back to 40. Is this normal?

 

I really doubt tire size has anything to do with it. Oil pressure is relative to RPMs and oil temperature. I think what you're seeing is your oil warming up and running at a lower pressure than cold.

 

That could be it. We have been having a cooler spell for the past couple of days so maybe thats what im noticing. Before i put the big tires on it was a little warmer so maybe im just paranoid about having problems with the bigger tires.