don't use M3 springs on an iX (long) (archive)

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A friend of mine who club races an E30 M3 and also owns an iX put stock M3 springs on his iX and hated it. Here is what he had to say:
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Everyone,

I have been away from the list for quite some time as I have been very busy.
However, I have been doing stuff and I wanted to share with everyone,
so.......

Some of you will remember that back in April of '99 I went through a major
dilemma of whether or not to cut the front springs on my '89 iX. I had also
planned on replacing the dampers with Bilstein HD's for improved handling
and ride quality. You may also remember the turmoil it caused to the list.
I will not get into why I did this unless someone specifically wants to
know. Anyway, I went ahead and did it and told everyone of my experience.
The procedure is written on Neil Deshpande's website (http://neilwerke.com).

Sometime after that I noticed a clunking noise which was occurring in the
front end. After some investigation I realized that it was the springs. At
first I thought that I had screwed something up during the whole procedure
and that it was not fixable....not easily anyway. So, I then purchased my
now totalled E30 M3. I decided to try the stock front springs from that car
in the iX.

At first I really liked the outcome. The ride height had not changed much
and the ride was a bit softer, better for crappy Detroit roads. Soon after
though I realized that it was undersprung. The springs were simply not
stiff enough to absorb the impulse bumps of these poor roads. Thus I
decided to return to the cut iX springs.

So, before I took them out originally to replace with the E30 M3 springs, I
determined that the cause of the clunking was improper reinstallation of the
springs. Simply put, I wasn't careful enough when I put it all back
together!

This time I was much more careful during the reassembly. Now I can say that
the ride is much improved. It is much stiffer but at the same time is much
less harsh. To qualify this I have driven the car over many different roads
and have compared it to the previous set up. This was a very good move
indeed on my part.

To reiterate some specifics, I cut 1.5 coils off. I did not bend the new
end to be flat. I do think one should do this if the opportunity is there,
it wasn't for me. Since I will be doing the wheel bearings someday soon I
will try to bend them then. But I digress....I roughly calculated the new
spring rate to be ~30% stiffer than previous. I haven't used real numbers
because I don't know what the stock spring rate is....and also because I'm a
bit lazy and haven't taken measurements. Someday....

Suffice to say, it is a big improvement. Now I also replaced the control
arms and the bushings. I had used E36 M3 bushings last time I replaced them
(not new control arms though, just bushings). They were still in decent
shape but since they really aren't removable without destruction I replaced
them. I installed the E30 M3 offset bushings. These, as we know, increase
the caster. On the iX the caster is different than non iX E30's as the
strut towers are vertical (or near it) instead of at an angle. I'm not sure
how much though. Of course the suspension geometry is different too so
maybe it's not too much different, I don't know. Now what this equates to
with the new bushings is much better turn in. In fact it's nonlinear.
Initial turn in (1/4 turn or so) is roughly the same as before but after
that it increases dramatically. I would say it's almost "darty". Some may
not like this but I have decided that I do. Previously, someone reported
doing this bushing upgrade on their iX and reported the same findings. I
suggested that with the different caster in the iX it may not be a good
upgrade. I was right and wrong. It is not the upgrade for everyone. One
must be a bit more careful during spirited cornering until properly adjusted
to the new feeling. ; )

On a side note, some of you may know that with a McPherson strut set up
lowering a car generally increases the roll center. The increased
propensity towards body roll is offset with the stiffer springs and usually
still results in better handling. Gustave Stroes has a nice write up of the
theory behind this on his website: http://e30m3performance.com.

So, for a summary, I definately like the cut springs. They improve
handling, ride quality, add a bit of stiffness and responsiveness, and
generally make the car feel more capable. The bushings add improved turn in
and quickness to the steering. I would also add that steering effort is a
bit increased but I find that I like that too. I should also point out that
I have not done an alignment yet and plan to do so when I replace the tie
rod ends soon. This may improve the dartiness, time will tell. I will also
say that there is increased noise in the car but it's not at all bad.

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