I'm currently running a 33x12.50-18 and I'm turning around 2,200rpms running 75mph. I'd considered going to a 35" tire which should keep my crusing RPM's right at 2,000. Will this help the fuel mileage?

 

I dont know for sure. i think it will but then you are also pushing more tire which equals weight. I would imagine it will tho. someone else will probably know more.

 

It has been my exerience that highway mileage is a function of air resistance (aka parasitic drag), which squares as the speed increases. the taller tires will tend to act as an overdrive, BUT will also raise the height of the vehicle which is generally 10% LESS mileage per inch raised.

The specific better fuel economy will result when you approach 1750 rpm for a stock engine, but while not exceeding 60 mph by much.

if you can put the 35's on, drop the body couple of inches, make them really skinny to help rolling resistance decrease, and pump them to 90 psi, you'll have a funny looking truck that gets better mileage.

 

Going up to 35's will drop mileage. Greater rolling resistance and greater wind resistance will totally override any gains you get by dropping RPM's slightly.

David Whitmer figured it out... taller gearing (numerically smaller), drop kit, and small tires.

 

Your telling me that my fuel mileage dropped 60% when i put a 6" lift on


It dropped about 12.5%, including tires

 

I think lowering the RPMs help lots, but only if you dont increase wind resistance...