Re: d60a2 shake

[ScharfR@aol.com]

In a message dated 97-04-02 23:30:57 EST, dans@ans.net (Dan Simoes) writes:

<< The culprits are either my MSW rims, a few years old but round to
 the eye, or the tires, D60A2s (the newer JLB) which have
 less than 5k miles on them.  Could it be a balancing problem?
 They were just done not long ago. >>


Wheel imbalance is not often a problem, in part because of the relative
homogenaeity of the wheel and the fact that imbalance takes on greater
importance the farther away the imbalance is from the rotating axis.  Thus,
tires are almost always the source of imbalance.  Wheel roundness is another
issue, but it can be quickly checked with a magnetic mount base and dial
indicator mounted on the car body to check for runout while the wheel
rotates.  Of course, if you have an A8, or no dial indicator, you could just
rig up a crude piece of chalk on a stick to a good solid mount while you spin
the same wheel and look for runout.

I would suspect your tires are the culprit, and balancing may not solve your
problem.  Some years ago I was involved in a statistical study of tire
balance requirements among a number of leading tire brands supplied to a
well-known car manufacturer.  Bottom line is that some brands are vastly
better than others in terms of what it takes to balance a tire. Worse than
that is that some tires will provoke shake and vibration even when
"perfectly" balanced.  The issues are conicity and roundness.

Simple example: Picture a square tire.  With enough weights, properly
located, it would be possible to achieve perfect static and dynamic balance
of a square tire.  Sure would ride lumpy though.  (For all you statisticians,
the obvious answer is a triangular tire; one less thump per rotation).

Your tires may be balanced, but not round.  Can't do much about it unless
they are new enough to be under warranty.  A tire that is not sufficiently
round to give a decent ride when properly balanced is an obvious candidate
for a warranty adjustment.