Re: Additional torsen stability factor - was Alignment

[quk@isham-research.demon.co.uk (Phil Payne)]

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