Unsprung weight question....

[repeater]

I'm trying to think physics here. It would seem to me (in my crazy head) that having more weight on the edge of the rotating mass would hamper performance more than having that same weight towards the center of the rotating mass. So that would lead me to this question..... Would there be a difference in performance, feel, and handling on a car with..... A 20 lb wheel and a 30 lb. tire compared to a car with A 30 lb wheel and a 20 lb. tire?? Just some food for thought. Although both cars have 50 lbs of unsprung weight on each corner, I would think the 30lb wheel / 20lb tire would have a better advantage. I could be wrong though - either way, it might be the same.

[ruknd]

[repeater]

Now I need someone really good at physics to either prove or disprove it.

[Inigo Montoya]

While I'm not "really good at physics", here's my thought: the more mass at the periphery, the more angular momentum, which is the product of the moment of inertia and the angular velocity.

The distribution of mass affects the moment of inertia. If you take the imaginary example of a cylindrical shell with all the mass in the tire and none towards the hub, the moment of inertia is the mass multipled the square of the radius. A solid cylinder's moment of inertia is half of that.

I suppose more angular momentum means that more energy is required to stop and start the wheel rolling, and less energy to keep rolling once up to speed. My impression is the difference between a 20 lb wheel with a 30 lb tire vs the opposite is negligible compared with the overall energy required to move and stop the mass of the car. Both situations are fairly close to a solid cylinder if you average the masses.

If someone else has a better explanation I am open to it.


(From the link below

Examples of Moments of Inertia (I) of Extended Objects:
uniform hoop: I = mr^2
cylindrical shell I = mr^2
long thin rod (about middle) I = 1/12(mL^2)
long thin rod (about one end) I =1/3(mL^2 )
solid cylinder I = 1/2(mr^2 )
solid sphere I = 2/5(mr^2 )

• more than you ever wanted to know about angular momentum

[fallzboater]

The suspension doesn't care, as far as unsprung weight and the suspension response goes. So the two wheel/tire combinations (equal total weight)will be equal for traction through bumby corners, etc.

The light tire/heavy wheel will be better for acceleration and braking due to less rotational inertia. In theory, also better for steering response (less gyroscopic effect), but probably negligeable.

Of course the best thing is to put the light tire on the light wheel!