Tire vibration: Longer

["Mike Nakamura" <mike_nakamura@xxxxxxxxxxxxx>]

This may apply, I do not have definitive knowledge or data and believe it
would be difficult to procure.  If the phenomenon I describe was ever
"real", I do not know.  If it applied 20+ years ago, but is no longer a
factor (with modern tires), I do not know.

In about 1975, our local Alfa Club hosted a speaker to inform us about
tires.

One of his topics was a phenomenon he called "Tire Forced Variance".

Symptoms:  Vibration that is wheel speed related on smooth surfaces.  Not
linked to engine speed, gear selection (could be neutral), engine on/off or
ambient air temperature.  The symptoms may be accentuated by tire
temperature or steering angle and possible masked by the application of the
brakes.  Symptoms may or not increase on cold tires.

Attempted cures:  Balance tire and wheel off car, balance tire and wheel on
car, check tires for separations, shave tires round, insure wheel is round
and true (straight), machine rotors, insure suspension is in good condition.
Not necessarily attempted in the order listed.

Possible cause:  Tire Forced Variance.  This was described as a differing
flexibility of the tire compound and/or belts.   This may occur in new tires
or develop as tires are used.  As the tire rotates the sidewall and tread
flex to present the contact patch to the road surface.  If a portion of the
tread is more or less rigid, when it flexes to contact the road surface, it
will cause a slight increase or decrease in tire diameter, thus inducing
vibration.

I'm guessing that almost all of us would agree that as tires age, they
change flexibility, maybe if the change is not uniform around the tire,
"Tire Forced Variance" could occur.

Granted, I have never heard of this described by any other "tire expert", so
I myself doubt it's validity.  I do know tires change over time during heat
cycles and exposure to the atmosphere.  Tire manufactures advertise their
improvements regarding tires aging.

Why would some cars seem more sensitive that others?  For instance, I have a
164 that I rotated tires front to back on the same side and now I notice
more vibration.  I have not had the tires re-balanced yet.  Re-balancing
will be my first attempt at a cure.  I am particularly leaning towards this
due to the fact that there are no weights on the outer rim of the wheel.  I
doubt the tire / wheel assemblies are in balance.  Moving to the front may
well have made the out of balance noticeable.

Could be a red herring or maybe for real?  Enjoy.

Mike

Bellevue WA, USA
mike_nakamura@domain.elided

91 Spider
94 164 LS
97 Bravada (Company provided hauler)
Will start search for a very good Montreal in a 3 weeks.

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