It does not help right now
but the new law just signed by Pres Bush
requires that new tires get a rolling resistance rating
stamped on the sidewall of the tire
similar to the
traction, temperature, wear range letters/numbers

The rough 'rule of thumb'
is that if the rolling resistance gets 10% worse
your MPG will go down about 4%

It does not sound like much
but some mudder tread style wide tires are 50% harder to roll
and MPG can go down by 20%
and if the tire lifts the truck or sticks out of the wheel well
it will also cause more wind resistance

 

Guess nitto wont be selling as many 325/60 R 20s[sm=boohoo.gif]

 

I got a 3" lift with 33" tires on my 2nd generation Dodge Ram 1500. Not only did it reduce my gas mileage, but I actually got worse mileage doing highway driving than city driving. I got about 12 MPG in the city and around 11 MPG on the highway cruising at around 65MPH.

 

Same story for me as everyone else, bigger rubber equals less mileage and often a reduction in your "butt dyno" response as you've changed your effective gear ratio. When went to a larger tires (from the factory 31's to 34's) I had already ordered the new gears before I even picked out the wheels / tires. But there was maybe a week after I had the tires put on with the stock gears (while I waited for the gears) and I was shocked at how different the truck felt. Seemed like it was working much harder....re-geared and got it back and then some

I've got several "oil burner" buddies who say the same thing happens to them. Their fuel mileage drops a bit, but they don't notice in the power department as much because the diesels have so much torque...