Tire size vs. gas mileage

I think you would have to do some pretty tight measuring to really see a difference in your mileage. It would LOOK a lot nicer with the bigger tires. I did it to my 97 Yukon and was pleased with the new look, and they didn't rub anyplace. Regards, JR

How can it not? If a tire has a (extreme example) 30% larger diameter, it's going to travel further given the same amount of engine RPMs. At some point there has to be diminishing returns due to more effort being required. My question has to do with where that point is reached.

tire size has nothing to do with gas mileage

A larger diameter tire has the effect of reducing the effective rear-end ratio. There is a well-known relationship between rear-end ratio and gas mileage. I expect that a 3% change in rear-end ratio would have a small impact on gas mileage - and a 3% change in tire diameter should have the same impact.

--Steve

basic physics.........you could run bicycle tires (if it were possible for them to support the vehicle weight) and the vehicle would get the same gas mileage

Yeah, but I wasn't talking about "drag". I was talking about tire size.

I think you're assuming that the engine is doing the same work and this may be the case if the final gearing is changed to give the same ratio based on a different diameter tire, but a larger tire is going to go further given the same number of engine revolutions. The engine may burn the same amount of fuel running at 2500 RPMs for one hour regardless of tire size, but the vehicle would have traveled a greater distance. MPG would increase.

Basic math.

Would, however a slightly fatter tire negate that difference due to additional drag?

There has to be a "sweet spot" somewhere.

Only if the tire was the same diameter as the old one. Also the thinner tire would get better mileage due to the reduction in surface friction. Has been proven many times.

It is FAR more than basic physics.