There are a couple of factors involved in tire clearance on the roundtail
cars. Okay, the same factors but with differing dimensions are involved on
the squaretails, but I'll try not to be too picky.
If the tire is short enough it will not hit the fender lip, front or rear.
This assumes the car has not been lowered, as Rocky points out. I've found
that "low enough" is a 185/60/13 street tire, or the 20" slicks mentioned.
A problem area with the cantilever slicks is clearence between the sidewall
and the radius arm on the rear suspension. If you have a roundtail car with
the arm in the stock location, you need to make sure that the distance from
the inner edge of the tire to the mounting face of the wheel you are using is
no more than 4.5 inches. On a 5.5 inch wheel using the 20 x 8 x 13 cantilevers
that translates to the backside of the wheel being about 3.25 inches from the
mounting face. If you have put the longer Mark 4/1500 axles on the back,
then you have an extra inch with which to work. If you move the pickup point
for the trailing arm inboard, you also gain some extra clearence room. Hmmm,
where's my little booklet from Kas...
On the front suspension, the wheel backspace is less critical, but you can
run into problems with the tire rubbing on the firewall during tight turns.
For the most part, with the tires sizes mentioned above this only happens
while moving the car around in the pits making really tight turns, and not
so much on the course.
On Killer, I have the longer axles from a later car and the wheels have 4"
backspace. I've used two sets of wheels, 6" ones with the cantilever slicks
and 8" ones with 20 x 8 x 13 non-cantilevered slicks. I've also run the 8"
wheels with 225/45/13 Hoosier Autocrossers. I've lowered the back of Killer
about an inch, and get rubbing on the fender lip. Depending on what route I
take with racing Spits, I may or may not flare Killer's fenders. Cranking
into a turn on the track and having the tire rub against the fender has got
to be a bug, and not a feature.
I do still wonder about tire choice at the VTR meet in Breckenridge. That
was the first time I ran Killer with the 8" wheels and non-cantilever slicks.
What this combo does is move the tire outwards about an inch per side compared
to the cantilver slicks on the 6" wheels. So at Breckinridge Killer was about
two inches wider than I was used to, and I do often wonder just how close I
came to some of those cones. A clean run and it could have been three in a
row. Oh well, Pugs in his Mark 1 on skinny little tires ended up with a better
time than I did, fair and square. Drat.
mjb.
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