>From Ken P. on 8/21/00:
>Tire uniformity other than obvious runout can sometimes
>really upset the steering wheel causing toraional nibble
>(shimmy) or steering wheel/column shake/vibration.
Good point! Recently ('98?) I had to put 3 different sets of
new tires on a C3 Vette in an attempt to eliminate shimmy. The
car had 20k mi and the front suspension & steering were sound.
The tire dealer insisted the shimmy was the fault of my car -
not the TWO different sets of brand new tires that I made him
put on the car in 2 days. I retorted that my car had no shimmy
until his new tires were installed...
What saved the day was the fortunate discovery of a second tire
dealer who claimed he knew "exactly" what was happening and had
the equipment to prove it. This small shop out in the boondocks
had a new-generation, multi-function, computerized Balancer that
just happened to measure Sidewall Force Variation (SFV) on tires.
At the time there were only two such machines in WI.
It had a wide roller that applied 700 pounds of force across the
face of the tread while the mounted tire was automatically rotated
at a very slow speed. Sensors recorded the tire sidewall forces
that were working in opposition to the calibrated load. Any tire
that exhibited more than 25 lbs of SFV was rejected by this 2nd
shop owner as a "problem tire", and he recommended not installing
such a tire.
To make a long story short, the appearance of shimmy on the Vette
was caused by numerous new tires from Dealer #1 that exceeded 30
lbs of SFV. A third set of 4 new tires (of a different brand!!!)
came in with readings of only 9-16 lbs of SFV and IMMEDIATELY all
shimmy vanished from the car. Just a thought...
Greg
VSCDA Sprite #517
Cedarburg, WI
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