[CorollaMaster]

Actually its an old racers trick. You can weigh your car by going out and using paper and a ruler. here is a link
http://www.rockcastle.org/activities.../weighcar.html

Thanks for the trick!

However, I wasn't actually trying to lower my contact area by changing the diameter of the wheel. I was trying to figure out which is better for gas in terms of rotational inertia: ie, which of the following options will the engine end up doing the least amount of work - having a wheel with a smaller diameter (so that more of the weight is in the center of the wheel) or having a wheel with a larger diameter (so most of the weight is towards the outskirts of the rim).

I had to pull out my book from highschool , but after brushing up on my physics a little bit, I think I figured it out.

While you want light wheels it matters where the weight is focused. If its towards the center of the wheel or spread out for that matter, its going to take less energy to accelerate because of the rotational inertia. However, with that said they will also tend deccelerate faster since they won't tend towards staying in motion. So if you plan on coasting or doing a lot of highway driving its not the best option.

Now if you could get light wheels that have a larger diameter where most of the wheel weight is focused towards the outer rim, then the wheel should stay rolling longer (kinda like it'd have more momentum). So this **should** increase mpg for highway driving and for coasting situations.

So I guess my conclusion at this point in the thread anyway would be that I want to find skinnier lighter rims that are larger than my current ones with most of the weight focused towards the outer wheel and then see what I can find for RR tires. this should potentially increase my mpg.

Thanks for all your responses so far! If you find anything more please let me know! I'll keep you posted on what I end up doing! Please keep on posting if you have more ideas!