Myth or fact?

Do bigger wheels help in gas milage? I figure that it would since the car travels further distance per wheel revolution. But some one said they can hurt gas milage in some instances. Is there any fact behind either of these claims?

larger diameter TIRES will because you turn less rpm on the highway.

However, larger wheels add unspring weight and hurt gas mileage

yea any wheel that is heavier than what u had before is gonna hurt gas mileage. just like anything that is added to your cars weight

air prussure does help your mpg tough.

A larger tire diameter will lower the rpm's for a given speed. The lower rpm's is where the gas is saved. If the tire is made narrower, there is less frontal area, i.e. less overall aerodynamic drag. This also saves gas, since you need less HP.

If the tire is heavier, or wider, it takes more HP to get to that speed, so you lose gas mileage there. Once at that speed, this is not so obvious.

In summary, yes, a larger (diameter) tire is like gearing the engine down a bit, similar to an overdrive, and saves gas at steady cruising only. It may use a bit more gas to get there though.

(Most of these points were already mentioned in the above posts)