My first set of autocrossing rims were aftermarket lugcentric rims. I
had no idea about them pesky rules and bought rims the wrong width and
offset, but no one complained (typical nice autocrossers). I decided to
use them for street and turn my street atick rims for autocross.
As soon as I got above 55mph on the street, I got a horrible steering
wheel shimmy. Discussing this another MR2 autocrosser, she said
explained the whole (hole?) hub/lugcentric deal to me. She had gone thru
the same thing and putting the little plastic rings on solved her
shimmy.
Well, I sold those rims instead. Using stock hubcentric rims, tthe
problem never appeared again. But years later, I started running 225
wide tires on the front of my car. This required a 1/4" thick spacer.
What this spacer did, was take the rim off the inner hub, changing the
rim from hubcentric to lugcentric.
I found that I could mount the rims, and the car was fine, but often the
shimmy would start up after a while, specially if I cornered hard, hit a
bump or pothole, or just drove 25+ miles. The worst case was driving to
San Berdoo (about 110 miles each way) on my R1s with the steering wheel
jumping like a caffienated poodle.
If I stopped and retorqued the rims, problem was gone. But only for a
while. Anything I did to "fix" this ended up only temporary and made it
seem like the "fix" worked..until it came back.
I never did the calcs, but I came to the conclusion that hubcentric rims
really need to be centered on the hub. Note, it did not matter at
autocross speeds. I think there is a difference between clamping force
holding the rim on, and the force required to make sure the rim does not
move radially at all. The smallest movement is magnified at higher
speed. Some cars are more sensitive to this than others. I have read
that the MR2 is one of them.
Thats my story anyway...
Randy Chase
'91 MR2 CS
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