Save gas tip, install lightweight wheels

[Kaotic Lazagna]

Gonna quickly chime in. I had two sets of rims, one lighter and one heavier. My heavier set gives me better gas mileage on the freeway, but poorer if it's city driving; and vice-versa.

[djct_watt]

Originally Posted by Kaotic Lazagna

Gonna quickly chime in. I had two sets of rims, one lighter and one heavier. My heavier set gives me better gas mileage on the freeway, but poorer if it's city driving; and vice-versa.

Same diameter, width, and tires? The biggest factor in rotational inertia (by an exponential factor is wheel radius and not weight).

Rot.Inertia = Mass x (Radius^2)

But in terms of maintaining speed (e.g. highway driving), I imagine that rolling resistance (tire and width) would be a bigger factor than weight.

Reducing wheel weight and radius will increase acceleration and braking performance, which will have a positive effect on city/performance driving. It's the reason that any REAL sports car has the smallest wheels possible that will clear the brakes.

I suppose that increased rotational inertia will help keep the wheels from losing momentum. However, any reduction in losses will be 100% offset by the increase in energy needed to recover lost momentum. I'd do the math and equations for all to see, but I'm just too lazy.

I think the gains/losses people tend to associate with bigger (and sometimes heavier) wheels are attributable to the fact that they use a completely different set of tires, hence making any comparison invalid (e.g. grip, handling, traction, etc), or they completely ignore the relevance of wheel width, comparing stock 185mm wide 15's vs 215mm 17's.

PS I have no idea if that even applies to you, Kaotic, (and I think it doesn't, but I'm just rambling venting about a complete different subject matter).

[flg]

I do better in the summer months than the fall and winter and spring. What hemisphere do you live in. Is warmer temperatures responsible for your improvement?
As many have posted wheel weight alone is an unlikely reason for such a gain. If you want better milage, don't install a CAI!