It really isn't that difficult to get modern wheels to fit on our roadsters.
All you need is a wheel and tire combo that is no larger than ~24" in overall
diameter and 9" in overall width. The 4x114.3mm/4.5" bolt pattern is very
common. The only two potential "problems" are the offset/backspacing, and the
centerbore. Different manufactureres seem to measure their offsets
differently, so I tend to go by the backspacing measurement. You will need at
least a 5" backspacing on a 15" wheel in order for it to clear the suspension
components in the front, and inner fender in the rear. But a 4.75" is even
more ideal, as with the 5" backspace wheel, the inner rim of the wheel will
just BARELY contact the upper suspension arm when you do a lock-to-lock u-
turn. And the rear tire will just barely scrub the inner fender when you go up
an angled driveway at ~2mph+.
Now about the centerbore issue: the roadster's front spindle seems to be a
major fatty! Most modern day rims are hubcentric, meaning that they are
supposed to have rings in their centerbore which allow you to center them when
installing. Well, this also means that a lot of these wheels don't have a
large enough centerbore to fit over the roadsters' front spindle, but no
problem, as a machined 1/4" spacer in the front should not only solve that,
but give a 5" backspace wheel the more appropriate 4.75" backspace.
Most modern 15" wheels have a width of 6.5"...and they will usually come with
around a 5" backspace. As the wheel diameter increases, so does the
backspacing in most cases. This is so that the larger wheel/tire combo can be
tucked in under a car's fender. That's bad for us though, becuase we need as
much room on the inner end as we can get! Now here's another note: a 16" or
larger wheel with a 5" backspacing can probably still be used, since its
larger diameter should allow its inner rim to clear the suspension arm when
you are turning it. But you will still want to make sure you have clearance in
the back.
So to sort of summarize, you can get the following:
- 15"x6"-7" wheel with a 4.5"-5" backspacing (and use a machined spacer in the
front in case the centerbore is not large enough to fit over the front
spindle) with nothing larger than a 195/55-15 or 205/50-15 tire
- 16"x6.5"-7" wheel with a 4.5"-5" backspacing (same deal with the spacer) and
a tire no larger than 205/45-16
- and yes, even 17" and 18" wheels can be fitted
You might want to look into brands such as racing hart and volk racing wheels.
They make modular 2- and 3-piece wheels that can usually be ordered in most
any offset/backspacing and bolt pattern. They're imported from japan though,
so be ready to shell out about 400-600 each. (That's for a 17" rim.)
Hmmm...well, that's all I can think of on the subject at the moment. Hope that
was helpful to someone. And if anyone's interested, I know someone selling
some nice 15" racing gear intermilano wheels. They're 6 spoke modern wheels,
with a 5" backspace and both 4x100mm and 114.3mm bolt patterns. They're
lightweight at only 11 pounds each. He's only got 3, but you should be able to
order a 4th one somewhat easily. If anyone's interested, you can give me an
email and I'll pass along the info. I was going to get these wheels for my
car, but I figure paint job first....and 15s are kinda small. :)
Van
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