[200q20v] FW: [audi20v] Re: Bump steer questions.

Bernie Benz b.m.benz at prodigy.net
Fri Oct 27 10:28:56 EDT 2000

FYI, my recent post to the 20V list.


> From: Bernie Benz <b.m.benz at prodigy.net>
> Reply-To: Bernie Benz <b.m.benz at prodigy.net>
> Date: Thu, 19 Oct 2000 18:14:24 -0800
> To: "Audi 20V" <audi20v at rennlist.org>
> Subject: [audi20v] Re:  Bump steer questions.
>> Pardon my ignorance, because I'm sure pretty much everyone here knows, but,
>> could you just for
>> my sake enlighten the list as to what one of these tests entails?
>> Chris
>> Interesting, I would like to know more on how this is done
>> and evaluated.
>> Thanks
>> Chick,
> Bump steer is the change in toe setting as the suspension, front or rear,
> moves through its free travel range.  Ideally, you want zero bump steer,
> i.e. the toe setting should remain constant and be independent of suspension
> movement.  Obviously, any toe change, resulting from bumps to one or more
wheels and body pitch and roll, can really screw up handling.
> So, to measure the bump steer characteristics of a suspension system, front
> or rear, one must measure the change in toe throughout the full range of
> suspension travel.  These measurements are best understood when toe change
> is plotted against suspension travel either side of the normal ride height.
> Any reference on suspension tuning will cover in detail how to perform the
> test, and give ideas on how to correct or minimize it, sometimes virtually
> impossible in a bad suspension design.
> IMO, the stiffer spring suspension "upgrade" is a crutch to reduce bump
> steer by limiting suspension travel.  Following this logic to the limit, one
> would replace the springs with approperiate lengths of 4" pipe.  Look, no
> bump steer!  Further, changing ride height may move the suspension travel
> zone into an area of higher bump steer.  You don't know unless you quantify
> your suspension characteristics and correct the problems.  Seat of the pants
> analysis is primarily responsive to the good fuzzy feeling of a lighter
> wallet.
> With zero bump steer suspensions, front and back, bumps as well as body roll
> and pitch do not cause suspension instability.  The classic Lotus race car
> design was soft sprung, but with a very stiff anti-roll system.  A dream to
> drive!
> Bernie
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