disscussion on tire size vs. MPG

[cantspell]

Hi there,
I'm aware that when you put on a pair of larger diameter tires, your MPG goes down? But I'm also aware that having a larger diameter tires, would reduce the number of rotations needed to travel a given distance vs. a smaller tire - right?

SO is it do to the acceleration that causes the MPG to drop with larger tires? So if one primarily did highway driving, a larger tire might actully benifit them???? Or is the increases mass simply too much, and reverses the effects of having a larger tire?

Now does any of this make sense - i just got up.

 

[Alec]

To a point...

Lowering RPMs on the highway will increase mpg to a point. At a certain point, your RPMs will be below the optimal powerband of the engine and you won't be running as efficiently. However, high gearing in the city really reduces mpg cause it takes a lot more engine work to move the tires. Higher gearing is also harder on your tranny.

IMO you want 2200-2700 RPMs at 70 mph. Above or below that and your gearing is wrong.

Right now I get 20 mpg on the highway with my 33s: proper gearing.