quattro digest, Vol 1 #4422 - 4kq vs 5kq rear suspension

[Larry C Leung]

Mike,

A Chapman Strut (first used on Colin Chapman's formula cars, hence the
name) uses
the driven axle as the upper link. The 4KQ (and UrQ) rear suspension, as
you say, is
simply the front in the back, in other words, it's got MacPherson struts
all around. The
limitations of MacPherson struts (and Chapman, for that matter) is little
ability to
compensate for roll camber changes, so as the body rolls (which older
Audis do
a lot of!) the outside wheels change from negative to positive camber,
losing ultimate
grip. Perfectly okay for a street car, as it limits the stupid stunts
that street drivers
would do by limiting the speed at which they go off and making the
sliding more
progressive and recoverable. It is partially why type 44's have a greater
tendency
towards understeer, as the rear suspension is more capable of camber
change
compensation than the MacPherson strut front end. It is possibly, it
street guise,
why 4KQ's and UrQs have that wonderful balanced feeling. They may not be
the
ultimate in handling grip, but they sure do feel good!

As for Chapman struts, the reason that they worked SO well for Lotus is
that they
(the cars) didn't roll much, so roll camber change wasn't much of an
issue. Also
the narrower tires of the day were MUCH less sensitive to camber compared
to
today's tires.

As far as best applications of MacPherson struts, I'd have to admit, BMW
seems
to do extremely well with them, some of the most capable M-strut cars are
from
BMW.

LL - NY




> Date: Fri, 03 Jan 2003 10:13:31 -0800
> From: Mike Veglia <msvphoto at pacbell.net>
> Subject: Re: 4kq vs 5kq rear suspension
> To: quattro at audifans.com
>
> I'm sure those much more experienced in suspension designs will
> chime in,
> but, I have never heard the phrase "passive assist articulated rear
> wheel
> steering" associated with 4kq rear suspension. Where did that come
> from?
> What does it mean?
>
> Anyway, the 4kq rear suspension is really the front suspension,
> backwards. I
> have heard it called a "Chapman Strut" design, but am not 100% sure
> it is. I
> adore 4kqs (and Ur-Qs of course) and have owned 4 of 'em to date (and
> drive
> one pretty much all the time now).
>
> However, the rear quattro suspension design first seen in the type
> 44 (5kq)
> is a much more complex and, arguably, better design for the larger
> chassis
> cars. The downside being a lot more bushings to replace when they
> wear out
> though. For a rather large and heavy cars, the type 44, C4, etc.
> quattros
> all are exceptional handling cars IMO.
>
> Mike Veglia
> Motor Sport Visions Photography
> http://www.motorsportvisions.com
>
>