OK, I'm getting barraged with off-list mail asking for setup advice, so I'm going
to kill multiple birds with a single stone here. Share And Enjoy!

DG's Guide to a Street Setup
----------------------------

This guide is all about how to build a decent street suspension, meaning a suspension
that handles well on the street, is robust enough to see daily driver duty,
but still has enough performance for the occasional autocross or track day.


I assume that you want a ride height lower than stock, that you're willing to
trade a little plushness for better handling, and most importantly, that "right"
is more important to you than "cheap" or "easy".

The cornerstone of a suspension is the shocks. You start with the shocks, and
then build the rest of the suspension around them. The shocks are (probably)
the most expensive components and they are the limiting factor for the rest
of the setup.

There's really only one choice for a street setup on a 2G, and that's the Koni
Sport (also known as the Koni Yellow) They offer good performance, they have
some adjustment range to them, and they're a nice durable component. Konis offer
better performance than the typical street shocks (Tokiko and AGX) and they're
more durable than the typical race shocks (Bilstein, Penske, and Moriss). They
also share with the real race shocks the property that they can be revalved
to better fit your suspension settings, although not as easily (ie, it's more
expensive to do so) than the more sophisticated shocks.

There are a couple of new makes on the block - JIC and Tein. I have zero experience
with them. I have experience with the Konis, and Koni has been around FOREVER.
Good enough for BAR, good enough for you.

Konis also have enough damping range to handle moderately stiffer springs. I
haven't done the math to see exactly where they slot in, but empirically they
seem to be OK up to the 400-500 lb range, with 500lbs being about the upper
limit (they sucked on 550s, personal experience) Given that we're designing
a street setup, you won't be anywhere near that much spring, so these shocks
will work fine.

Now that we have our shocks selected, springs. Absolutely, positively, make-no-bones-about-it,
stay the hell away from "lowering springs". They tend to be marketed as entry-level
parts, meaning that the quality of the steel and the heat treat is usually sub-par,
meaning that they'll sag on you. You also are stuck with whatever rate and ride
height they were designed to, and 99 times out of 100 either the rate, the ride
height, or BOTH are not what you want, and you're stuck.

They're also harder to install.

So that means coilovers. A "coilover kit" consists of a threaded sleeve that
fits over the shock, and a threaded perch that screws onto the sleeve. With
these installed, changing ride height is a simple function of screwing the perch
up and down. This makes fine-tuning the ride height a simple task.

But the real advantage of the coilover kit is that they use Real Racecar Springs
- standardized springs that come in a wide range of lengths and rates. They
are of exceptional quality, and because the same spring is used in a Trans-Am
car, or a WRC car, or a Super Touring car, or all manner of Real Race Cars,
economies of scale take over and they are both CHEAP and readily availible.
A single 2.5"X8" Hypercoil runs on the order of $50 each, and they hold value
reasonably well, meaning that you can play around with different rates and sell
off your surplus springs without too much trouble.

Eibach makes coilover springs too. I have had them sag on me. I run Hypercoils
now.

Ground Control sells a coilover kit that works well with the Konis, although
they use Eibach springs. They may substitute Hypercoils if you ask them to.
I also think Moriss Dampers has the ability to produce a similar coilover kit,
and he uses Hypercoils now - it never hurts to call and ask.

The next big question is "What rates should I run"?

There really isn't a definitive answer to that, as it depends a lot on the actual
weight of your car, your corner weights, your unsprung weights, how much cargo
you routinely carry, the state of your local roads, and how willing you are
to trade comfort for performance. Different people have different opinions on
rate, and there really isn't any definitive information until you move up to
real shocks and sticky tires.

I'd suggest no stiffer than 500/400, and 400/300 is a decent starting point.
I once drove from Florida to Detroit, in the winter, with my wife and our luggage,
with 400/300 over Konis and the drive was just fine for both of us, so that
may be a starting point for you.

There's one more part you need though. The DSM suspension is designed such that
the shock/spring assembly pivots around the upper rod mount, especially the
front in steer. You can see this firsthand by jacking the car up, pulling a
front wheel, and watching the shock as an assistant moves the steering from
lock to lock. See it move?

The stock springs are soft enough that Mitsu can get away with this, but once
you go to a coilover and stiffer shocks, this is no longer an option. Instead,
the upper spring perch *must* remain co-axial to the shock rod so that there
is no bending moment on the spring.

I attended a Claude Rouelle Vehicle Dynamics class earlier this month (42 hours
of instruction in 3 days, given by a former F1 engineer) and one of the topics
discussed was bending moments on shock rods. You can now get special perches
designed to equalize the assymetric pressure of a spring on a coaxial perch
that comes from the way the spring is wound. (The last coil on the spring is
ground flat and so, being of non-constant diameter, applies a little more force
to once side of the spring than the other) When I told him about the Ground
Control upper mount, he was horrified - and I have seen with my own eyes how
much the spring bends when using these mounts and steering the car.

So you will need a coaxial hat upper mount, and with it, a mount plate that
uses a spherical bearing to locate the upper end of the shock rod. Moriss Dampers
makes and sells these.

Now normally bearings have no place on a street car, as there's a large increase
in NVH associtated with them, but these ones work out pretty well. There's lots
of rubber elsewhere in the shock mounts to keep the car quiet.

So you're looking at:

- 4 Koni Yellows
- 4 coilover sleeves and perches
- 4 8" X 2.5" springs
- 4 coaxial upper hats and bearing mount plates

Now, 2 words about setup.

Installing these parts is simple and straightforward. (A helpful trick is to
disconnect the sway bar end links) But once installed, there are two things
you must do.

The first is get the car corner weighed. Set the ride height initially so that
you have a 2 to 3 finger gap between the tire and fenderwell arch. (and each
time you change the ride height, bounce the car a couple of times and roll it
forward and back a car length or so to get it to settle) That'll get you suprisingly
close on the weights, but you still need to set the weight on the scales. Any
decent sized race shop will have scales or will know where they can be obtained,
and the process is fairly easy and cheap. Many places will set weights in exchange
for beer.

Once the weights are established, you can raise and lower the car without disturbing
the balance by raising/lowering each adjuster the same number of turns.

Once weights are set GET THE CAR ALIGNED. What you are worried about is NOT
CAMBER, but TOE.

DSMs have "bump steer", which means that the toe on each wheel changes as the
wheel goes up and down. As you lower the car, it toes out, and even small amounts
of toe out eats tires like no tomorrow. SO YOU MUST SET TOE EVERY TIME YOU CHANGE
THE RIDE HEIGHT. NO EXCEPTIONS! I MEAN IT!!

With this setup on the car, properly corner weighted, and with the alignment
set you have a car that should handle very nicely with a comfortable ride and
no tire wear issues.

DG

Click to expand...