thanks i never really thought about that. am i correct in assuming that it wont be too drastic of a change between a 245 and a 255 tire?

 

^^I don't think so. More difference will be seen going from all season to a summer only tire. When I had my camaro, I ran 245/50/16 summer only in the none winter months, and a 215/60 or 65/16 for my snow tires. In the winter, my mpg would almost mirror my summer mpg (instead of going down). I attributed this to the snow tires having less friction (mpg goes up), but also to less btu's in the fuel (mpg goes down). I'm talking a few points here (2-4 mpg?). If you drive like a nut then fuel costs are probably a great concern for you Otherwise, it's something to keep in the back of your mind. Nothing is free, there's always a tradeoff.

 

Between tires of the same class, the mpg difference will be marginal. I have a couple hundred tanks on record including what i changed along the way (i.e. larger wheels, smaller wheels, lighter wheels... ditto on tires, lighter rotors, change in oil brand, etc....) My drive is pretty much the same day-in, day-out. The difference is negligible IMHO... about 1mpg at the most. I can vary mpg that much just by changing driving styles within the same week.

Here's an old post of mine, i haven't updated it in a while but do have the #'s from that point to the present and the variance is the same.

Mods vs. MPG - G35Driver

 

Ditto for me, went from 245s on 20x8" rims to 295s on20 x 10" rims and my mpg has only dropped at most .5 mpg, and that may be that it's tougher finding gas w/ less ethanol, they always seem to be sneaking more of that crap in our gas these days

 

here's the math worked out Tire Width - Nissan 370Z Forum you should read it too, op. might give you some baseline design options for selecting tires. gluck op.
i posted here a while back but no one every gave it much of a though or comment.

 

seems like it should be an interesting read. thanks jujubii