RE: They call me the wanderer...

[Luis Marques <marques@ti.com>]

In a message dated 2/3/99 JustaxPHX@aol.com writes:
<< As the resident suspension curmudgeon, I must point out that,
technically speaking, lowering your car doesn't have any effect upon
bumpsteer since you're really just moving to a different static point
along an unchanged curve. That said, it might be possible that your
suspension is now operating in a part of the curve where bumpsteer is
more prevalent -- it is usually worse at the travel extremes but not
always -- thus you're noticing it more than you did before. >>

I don't fully agree with the first statement, but the second statement
is what the bump steer problem in lowered cars is all about.  Bump steer
results when your tie-rod pick-up point moves laterally a different
amount than your a-arm pick-up point when the suspension is
compressed/extended.  In simpler words, you toe changes as a function of
suspension travel.  Ideally, the suspension/steering geometry is
designed such that this toe sensitivity to suspension
extension/compression is minimized throughout the whole range of
movement, and it's traditionally achieved by using tie-rods that are
about as long as the a-arms and parallel to them.

Many times, compromises are made and the result is a suspension that
can't maintain toe constant throughout it's full travel.  Case in point
is the Audi steering rack where both tie rods are attached to a point
very close to the center of the car, resulting in long tie rods.  The
band-aid fix is to at least design it so that toe isn't very sensitive
**around the usual ride height**.  So the a-arms and tie rods are more
or less parallel only at the std. ride height.  What this means is that
your Audi isn't really prone to bump steer at stock ride height, but if
you lower it, the toe will be more sensitive to bumps on the road. 
There is no easy fix except to drive in smooth roads.  The real fix
involves moving the steering rack or the tie rod pick-up point on the
struts up or down, or somehow shorten the tie rods (and moving the rack
attachment point outward).  And this would only work at the new lower
ride height.  Easier solution is simply to not lower your Audi all that
much.  Please note that this applies mainly to the older models.  I
don't know how the newer front suspension designs like the A4'a would
respond to lowering (but I have a hunch it will be better).

-Luis Marques
'87 4kcsq