I was wondering which settings would be best to correct for my tire size. I am running Michelin LTX M/S LT265/75R/16E tires and the Michelin site says that the tire is 31.8" in diameter. The PPE Programmer says that I should measure from the ground to the top of the tire and it measures around 31.00". I don't have a GPS to check for accuracy. Which tire size should I use for the most accurate results?

I just installed a PPE programmer on my truck, and I went through the same thing. You should measure from the ground to the top of the tire. This will make your tire size correct for your speedometer. I have 285/75-16 and I set it for 31" and the speedometer is good now. I checked it going by a road-side radar station. You will probably need to set it around 30-30.5".

Someone said something once about this and it was 30.8 IIRC that got them closest to the actual mileage..

I just went to the tire manuf. website and took their numbers off the spec. charts. That got me dead on with the ppe.