RE: Additional torsen stability factor - was Alignment

["Smith, Kirby A" <kirby.a.smith@lmco.com>]

I think this scenario requires non-linear tire behaviour, which of course
tires actually have (breakaway), but the effect needs to be explicitly
incorporated into the argument.  If alignment made the rear loose to begin
with, there would seem to be less understeer entering the corner to begin
with, and the car might be more neutral.  Also while all this is happening,
the chassis is transfering weight and the driver is likely doing something
to the steering.  It would be interesting to enter the corner with fixed
steering and bad alignment and see if U-O-U happens.  If it does, is it
quicker than body dynamics time constants. 

Your argument suggests that handling may be drastically modified by not only
alignment, but slight tire size variations, and tread pattern variations.
For example, assume perfect alignment and rear tires with lower traction
than the fronts, in extremis.  Then rather than a simple Oversteer result,
you might expect the U-O-U of your paragraph (c).  I think this alone
extends the alignment argument to other factors. 

kirby

> -----Original Message-----
> From:	quk@isham-research.demon.co.uk [SMTP:quk@isham-research.demon.co.uk]
> Sent:	Tuesday, October 19, 1999 10:29 AM
> To:	kirby.a.smith@lmco.com
> Cc:	quattro@audifans.com
> Subject:	Re: Additional torsen stability factor - was Alignment
> 
> In message
> <A955A4BCA8F8D011AE1C0000F804A88A0413C733@emss05m02.sanders.lmco.com>
> "Smith, Kirby A" writes:
> 
> > In summary, Phil believes its all due to alignment.  In keeping with
> Gary
> > Lewis' request for new factors, I submit the following, with all due
> > respect, and in full anticipation of becoming a flack target.
> 
> > I suggest that while alignment can change a car's intrinsic handling (U
> or
> > O) and thereby make the vehicle more or less controllable, a U-O-U
> > oscillation, such as reported by Scott and Jeff, requires two lags
> through
> > the servomechanism made up of vehicle and driver.
> 
> I don't think so.  Imagine the following scenario:
> 
> a) An ur-quattro.  As most of us would probably accept, the ur-quattro
>    is prone to understeer by nature of its weight distribution. This
>    was a deliberate choice by Audi, and you can demonstrate the effect
>    by entering a corner too fast with the power off - the front drifts
>    out.
> 
> b) Now imagine an ur-quattro with the rear toe set dramatically badly.
>    In such circumstances, both rear tyres are actually slipping sideways
>    even when the car is going in a straight line.  In a bend, this slip
>    might be enough to reduce adhesion at the rear enough to overcome
>    the native understeer of the car.  I believe this (exacerbated by
>    the next factor) was what caused the event I experienced and which
>    has since been fixed by tightening the rear wheel bearing and
>    realigning the rear axle.
> 
> c) Now imagine power applied through a device sensitive to slip, in that
>    it moves torque about, and in a corner with power on.  The good old
>    understeer starts, the front axle slips, and power goes to the rear.
>    If the rear is pre-disposed to slip because of, e.g., bad toe, then
>    the shifted torque may produce a greater slip effect than it had
>    at the front and understeer will very rapidly become oversteer.  Slip
>    then becomes worse at the back than at the front, and the dear old
>    Torsen shifts the torque back - making the understeer worse again.
> 
> This, IMO, is what's happening.  It's bad alignment, especially at the
> rear.  My car is now booked in to BR Motorsport this Thursday, and I'll
> see if I can get a copy of the Type 44 specifications.
> 
> --
>  Phil Payne
>  UK Audi quattro Owners Club
>  Phone: 07785 302803   Fax: 0870 0883933