re: <E36><M3> X-Brace

[Ron Katona <ron3b@xxxxxxxx>]

Mike A. wrote:
> How does the x-brace affect steering characteristics in the M3 (95 E36)?
> I'd expect that making the front end stiffer would create more understeer.
> If so, does a rear tower brace help balance it out?

Not an M3 specific answer because I don't drive one, but generally the
x-brace reduces understeer in E36 cars. Some notice more of an effect
than others. The effect on my car was quite noticeable, about as much as
an aftermarket set of swaybars.

The spring rate is not affected, so the front end is not stiffened.
Neither the springs nor the strut tower gain any stiffness, so the usual
handling rules of thumb (stiffer in front = understeer) don't apply to
this mod. What the x-brace does (from looking at it during the install)
is to reduce or eliminate lateral movement of the stock crossmember and
the front chassis rails by tying them in an X pattern to the chassis
just behind the firewall.

When the car corners, the force from the tires/wheels is applied to the
hub, then the lower control arm, then the crossmember, then the rails
which turn the car. My take on it is that under heavy load, the
crossmember and rails deflect laterally. This brings the lower part of
the suspension in towards the engine on the outside wheel. That causes a
change towards positive camber on that wheel. The x-brace helps stop
this lateral movement and retains more of the static negative camber.
How much does the stock set up deflect? Beats me, but in my relatively
stock car the difference in handling was significant during the first
autocross after the mod. Normal driving won't show any real benefit.

The rear tower brace doesn't enter into this equation and is said to be
of limited value.
- -- 
Ron Katona

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