A few comments on comp springs and rear shackles:
The comp rears are very stiff, way too stiff for normal street use and generally
too stiff for race use. Road racers like a bit more understeer - it's
disconcerting to get the tail out in a high-speed bend. Autocrossers can
tolerate more oversteer because the speeds are lower and being a little twitchy
is sometimes a good thing. Just be sure you cut the bump stops down (like cut
them in half) or it will be REAL twitchy. When the frame bottoms on the axle,
the effective spring rate becomes infinite and you get very sudden oversteer.
They lower the car about 1-1/2" to 2" as do the comp fronts.
Personally I like the way the car sits with comp springs all around. Yes, I run
them on my car and I had them on there when it was a daily driver (back in the
day) but I was a lot younger then. I can put up with them for good-time drives
now.
I wouldn't recommend switching the shackles around. I did this a long time ago
when I put on the comp springs and found the tire/wheel combination wouldn't
clear the inner fender. I thought it handled fine, but when I started
autocrossing a few years later I found out how bad it really was. I swapped them
back (had different tires by then) and it made a huge difference.
If you need a little bit more height in the back to clear the tires, consider
putting an extra leaf in the springs or using bolt-on coil-overs on the shocks.
Yes, I know that will wear out the shock bushings faster because they weren't
designed to support vehicle weight, but I think it's better than flipping the
shackles.
Offset on the rear wheels is critical. Most Z wheels have closer to zero offset,
whereas the roadsters need about 3/8". Again, this depends on several variables,
like the tire you are running and how straight the body is on the chassis. I had
one brand of 185/70-14 tire that would clear and another that wouldn't even when
using the exact same wheels. If you are buying wheels, go for a little more
offset - you can always use thin wheel spacers to move them out, but you can't
move them in if there is too little offset.
There are no absolute rules other than "Try it and see."
Gordon Glasgow
Renton, WA
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