Over the years, Iíve tried several tire combos and read literally thousands of posts of what guys got and can make an easy generalization:
If you put substantial larger or smaller outside than OEM diameter tires, expect to see a reduction in MPG
. The boys at the factory do have a handle on this.
Bigger tire, counterintuitively get worse MPG
than OEM-sized rubber because of increased rotational moment of inertia. ROI is the measure of how effective a wheel is at being a flywheel (storing rotational kinetic energy). Before you accelerate the truck, you must accelerate the tires first. ROI goes up with the square of the radius, so if you go from 31.7Ē OD
OEM rubber to 305s you will see a 15% increase in ROI.
This would not have any effect if you drive the same speed all the time, but that isnít the way anybody drives. People start and stop, speed up and slow down. Every time you do the rotational kinetic energy state of your tires must change. That means you either wear your brakes or burn fuel.
Likewise, tires or a smaller OD
get worse MPG
because they make your engine rev up more at a given road speed. Higher engine RPM generates higher engine frictional HP and that increases fuel burn.
If you change tire size, get your speedo corrected. If you donít correct your speedo, you are driving your ECM crazy and you are lying to yourself.
Always air your tires up to the maximum pressure on the sidewall of the tire. These trucks are VERY sensitive to tire inflation. Soft tires can cost you 1.5-2.0 MPG
depending on season. Tire inflation varies itself a lot in colder months. I run very high pressure in my 235-85E tires but I donít recommend it unless you are as crazy as I am.