Question about steering wheel shaking while driving

[Gaz64]

Originally Posted by SBSerpent

Very interesting concept indeed! I have had some similar thoughts along this line in trying to understand my wheel shake that comes and goes at speed.

When I drive along a smooth, straight road keeping a constant throttle and maintaining a constant speed (lets say 65 MPH), I have a wheel shake that comes and goes as I drive. Roughly speaking, its cycling every several seconds.

I have 255/40s on the front and 315/35s on the rear (17" wheels). The diameters of these tires are 25.0" and 25.7" respectively, which comes out to a difference of 2.2" between the tire circumferences. What this means is that both front and rear will not remain constantly in synch when you travel in a straight line. Based on some rough calculations, after about 18 revolutions, the tires will be 180 degrees off from each other. Another 18 revolutions and they will be back to where they were with respect to each other 36 revolutions ago (again, approximate).

So I'm thinking that there is some sort of harmonic going on where, depending on where the tires are with respect to each other, i am getting a pronounced shake or nothing at all since whatever imbalance there is is cancelling itself out. Hmmmmmm.

A front imbalance cannot be cancelled out by a rear imbalance.

Two front wheels can cancel each other out, and so the steering wheel can shake at around 50-70 mph typical, and then cycle on/off.