Quote:
Originally Posted by gasti_ako
it doesn't matter if you are using 13s or 18s...
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It generally will matter if you are using 13s or 18s. Unless you've got some really tall tires on the 13s, the overall diameter of the tires on the 18s will be larger. That will make your overall effective gearing taller, which will cut your RPMs/mile down, which will be good for your fuel economy when cruising at steady state.
Offsetting that (probably by more than you gain from the taller gearing) is the general tendency for the larger wheel/tire combo to be heavier than the smaller one. Which means that you lose fuel economy when you accelerate, plus (I think!) a little bit more when you go over bumps. Since pulse and glide is all about accelerating efficiently... You can see where that goes!
So there are effects both ways, but for almost everyone the larger heavier wheels are a loss.
-soD