Basic question.... larger wheels... better, worse or same gas mileage?
 

Lame as far as questions go on here.... but I had to know. Sometimes you have to suck it up and ask the silly questions.

my avg mileage went down when i went to 18"s
 

the trip computer used to say 21mpg on my stock rims but now i'm getting about 18mpg with my 18"s.

Well
 

It depends more on the overall rolling circumference of teh wheel+tire, as well as the weight of them.

If they are the same, then it won't change :)

-T

So, based on your scientific observations, do you really think your gas mileage went down 14%...
 

...because of 18" wheels? I think not. A taller wheel/tire combination (i.e., 235/40-18's that are 1.7% taller than OEM 225/45-17's) should probably theoretically allow better gas mileage since you are turning 1.7% less RPMs for any given speed; although your trip computer and odometer will understate mileage and MPG 1.7% as a result of this swap, and the tires may weigh a tad more, so there is more resistance involved, although probably not enough to offset the 1.7% difference.

When I had an '86 Suburban and put tires on roughly 10% taller than stock, I think my mileage did increase a little bit, and I'm certain the acceleration slowed, since that effectively gave it 10% higher gearing in the transmission.

Why does it matter.
 

your car is $40k and your worried about fuel mileage

It sucks to go for a drive and have to stop every 250 miles to fill up. It matters.

I'm a bit rusty on my physics, but the longer radius means greater torque is needed to turn the
 

wheel so it would require more energy to be expended to turn the wheel. Taner had a good point it depends on the weight of the wheel.
My first thought is that bigger wheels would equal lower gas mileage, but there are a few factors that could influence that.

anyone.... anyone....

get a 20 gal fuel cell and some jerry jugs

Chalk it up to curiosity. I've come to terms with the gas mileage. even with that i'm not alone...
 

you don't come from driving a japanese econo car into a gas guzzling german sports sedan and not notice the difference.

I just wanted to see if my logic was correct in explaining the impact of larger versus smaller wheels.

mmmmkay

Acura Integra gsr.. 2 in fact a 96 and a 99