Increasing Gas Mileage With Taller Tires? Options

[joyworks]

One of the few things that I dislike about my '99 Celica Convertible is that the gas mileage isn't as good as it could be. The 1997-2001 Camry, which had the same engine, got 3 mpg better on the highway with a 5-speed than my Celica does with a 5-speed, and the Camry weighed about 300 lbs more! I can only attribute this to the high revs of my Celica's 5th gear. So, my question is, can I achieve better fuel economy with a larger diameter wheel/tire combination? I know it would throw my speedometer off a bit, but to save fuel, it would be worth it to me. On that same note, what would would the tallest tire that I could put on a 16" rim and not suffer from any fender rubbing? What about a 17" rim? Thanks for your help!

[playr158]

well you are correct still i suppose.

"In a ground vehicle with a suspension, the unsprung weight (or, more properly, the unsprung mass) is the mass of the suspension, wheels or tracks (as applicable), and other components directly connected to them, rather than supported by the suspension. (The mass of the body and other components supported by the suspension is the sprung mass.) Unsprung weight includes the mass of components such as the wheel axles, wheel bearings, tires, and a portion of the weight of driveshafts, springs, shock absorbers, and suspension links. If the vehicle's brakes are mounted outboard (i.e., within the wheel), their weight is also part of the unsprung weight."

i guess we can say a wheel is/should be both unsprung and rotational mass.

we should be more specific and state that during rotation weight is the same but mass increases as a function of speed.

rotational mass effects the car during acceleration and the effects of the work required to accelerate a heavier object.
heavier wheels result in slower acceleration, where as lighter wheels result in faster acceleration.
this gets into a whole event of rotational dynamics, moment of interia and such.

but easy way to say is....dyno on 18s and dyno on 16s...and the 18s will dyno less power.
it takes more work and force (ie more gas) to move larger and/or heavier wheels.

end story is removing weight from things that spin(wheel) can be more beneficial than the same weight of something that doesnt (sub box)

This post has been edited by playr158: Oct 23, 2008 - 7:20 PM