[urq] Eibachs

Eric Renneisen racingiron at comcast.net
Fri Mar 17 19:14:56 EST 2006

OK, here's what I found out from the Eibach tech guy:

- They only show the 1511.140 kit for the urq, and it's discontinued.
It's progressive both front and rear.  Based on the front P/N, this is
what I believe I have on the '86.  Eibach has no listing for a linear
kit for this car.  Martin, maybe the linear kit you reference is from
Europe?  The guy I spoke to said he could not look up Euro P/Ns in his

- Martin, your 4KQ kit (90Q) is European (obviously, since the car was a
Euro import).  They couldn't give me any specs for it, but it should be
close to what we got, if not identical.  Are they mixed

- The 4KQ kit available here has noticeably lower rates than the urq
kit, which explains the lower ride height, especially in the front.  The
front is progressive and the rear is linear.  Oddly, the rear spring is
the same as the front on the 80Q/90Q (and on the 4K FWD!).  It's rate is
also higher than the final rate of the progressive front spring, which
leads to speculation that the kit is specced backwards.  Eibach guy
thought it looked weird, too.  Comparing the front 4KQ spring to the urq
spring leaves no wonder why we'd have problems with a low front end.

- The 80/90Q kit uses the exact same rear progressive spring as the urq
kit.  The front is linear.  Based on the front spring P/N, this is what
I believe is on my '85.  For an urq, this is certainly a better choice
than the 4KQ kit.  However, I did notice that with the '85 LF strut on
the '86, I did get some slight fender rub during hard compression, and I
vaguely recall the same when the '85 was mobile.  Using some of the
figures from Eibach, static ride height with this front spring would be
about 4mm lower than the urq kit, and the linear rate is much lower than
the upper range of the urq spring.

Here are the rates and P/Ns for the various Eibach springs:

urq (1511.140 kit):
front (1511.001) 120-200 lbs progressive
rear (1511.002)  120-200 lbs progressive

4KQ (1504.140 kit):
front (1504.101) 108-137 lbs progressive
rear (1510.001)  143 lbs linear

80Q/90Q (1510.140 kit):
front (1510.001) 143 lbs linear
rear (1511.002)  120-200 lbs progressive

The astute reader will notice that the front and rear urq springs are
the same rate, and the rear spring is still available as part of the
80Q/90Q kit!  I immediately wondered if that rear spring would be
suitable in the front as well.  Unfortunately, there is a difference in
length.  The free length of the rear spring is 2cm shorter, and worse,
under load the rear one would be 2.5cm (1") shorter (I have to assume
the two springs don't "progress" at exactly the same rate).

So there it is.  I'm happy to have the correct kit on the '86, but I'm
not too enamored with Eibach.  The weirdness with the 4KQ kit and the
mixing of progressive and linear on the same car just makes me scratch
my head (of course, I'm no suspension guru).  I've never really been a
fan of progressive springs anyway.  If we could find an alternative that
provided a reasonable ride height and linear spring rate, I'd gladly

Eric Renneisen
'86 urq
'93 S4

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