Because I pull a 5th wheel trailer, I keep my rear tires at max allowable pressure (80 psi) and the front at 65 psi. It's a little harsh when the trailer is unhooked, but is smooth when connected. I also keep the trailer tires at max. (56psi) because the greatest cause of tire failure on trailers is underinflated tires, I'm told. It also helps the mileage. Running underinflated tires is like pulling a load uphill.

My on-board mileage calculator tells me I get 13.3mpg with the trailer hooked up and 19.4 running empty. That is on trips of about 100 miles or more. If the calculator is anywhere close to correct, I think that is good mileage.