# Rotational weight vs. dead weight

I am not sure if I am in the right section, but here goes my question.

Can anyone explain to me which one would be heavier. A rotating wheel or a wheel that is just sitting there?

Doc Al
Mentor
Why would you think there would be a difference?

well the main debate is "will bigger wheels cause my mpg to go down?"

my answer was is that at a constant rate it would actually increase.

a buddy of mine puts his 2 cents in and states that rotating mass is a lot heavier than dead weight. i am just trying to make logic of that.

Hootenanny
Staff Emeritus
Gold Member
The answer to you first question is that both still have the same mass.

To answer your "will bigger wheels cause my mpg to go down?" question, you would have to consider the moment of inertia of the wheel and work done.

~H

Doc Al
Mentor
The weight of a mass is the same whether rotating or not.

The car not only needs tp propel the "dead weight" of the wheels, but also must generate an angular velocity and acceleration of the wheels, which is determined by calculating the mass moment of inertia. so a heavier "dead weight" would increase the moment of inertia, lowering gas mileage.