[rallybull]

I had been doing some research on trying to find an answer to the question:

Does a light weight wheel increase the amount of bumps that the passengers feel or does it actually decrease the bumps?

There seems to be some amount of misinformation on the internet on this subject and perhaps I'm guilty too of adding to the misinformation in a separate thread on this forum on the M-performance suspension.

I consider tirerack a credible source for information and they feel that heavier wheels improve the comfort. Here is a link to a tirerack article: http://www.tirerack.com/wheels/tech/...jsp?techid=108

Here is a quote from that article:

On the road, this combination was only praised for its ride quality. Our experience showed that the heavyweight wheel's reluctance to be moved as the vehicle rode over expansion joints, patches and potholes actually damped the impact harshness transmitted to the suspension, and forced the tires to absorb more of the jolt.

On the other hand I found at least a couple of articles that have stated that by increasing the sprung to unsprung weight ratio (like by reducing wheel weight?) the bumps actually reduce.

Here is the first article which seems pretty well written:

http://www.rqriley.com/suspensn.htm

Here is a snippet from that

Early pioneers believed that the primary job of the suspension system was to absorb bumps and smooth out the ride. Today we understand that an equally important function of the suspension is to keep the tires in contact with the road. This is not as easy as it might appear to be. When a tire encounters an irregularity the resulting forces tend to reduce contact pressure and therefore degrade adhesion. Obstacles impart a vertical acceleration to tires that increases in proportion to the forward speed of the vehicle and the size of the obstacle. The greater the accelerated mass (unsprung weight) the greater the kinetic energy. In a sense, a raised obstacle throws tires away from the roadway. A depression causes the surface to rapidly drop away leaving the tire to follow along when inertia can be overcome by the downward pressure of the springs. Both occurrences reduce the tire's contact-pressure and tires can actually become airborne if the forces are great enough.
The forces generated by roadway irregularities (bumps) must be overcome by the springs in order to keep tires in contact with the road. The force of the springs comes from the compressive load imposed by the weight of the vehicle. The lighter the vehicle, the less compressive force is available, and the easier it is for the vertical motion of the wheels to overcome the inertia of the sprung mass and transfer motion to it as well. The ideal combination occurs when the ground pressure is maximized and inertial forces are minimized by a high sprung-to-unsprung weight ratio. A high ratio keeps the tires more firmly in contact with the road, and it also produces the best ride.

Also wikipedia article on unsprung mass actually makes it a bit clearer:

http://en.wikipedia.org/wiki/Unsprung_mass

It appears that lower unsprung mass (like lighter wheels) results in a less bumpy ride over poor roads. However, the downside is that it could increase the "fine vibrations" that you feel over some "relatively smooth surfaces" such as concrete roads or an asphalt road with gravels.

Based on the above, I would like to conclude that tirerack was actually wrong in making that statement. Light weight wheels do make for a less bumpy ride.

Anyone care to agree/disagree?