over/under - steer and tyres

[QSHIPQ@aol.com]

Dave E writes:
>*not* wanting to re-enter the torsen deba[cl][t]e, but you must remember
>that running different wheel sizes benefiting an ur-quattro depends very
>much on the type of ur-quattro you're talking about.  understeer (and lots
>of it) was a known affliction of the generation 1 cars, and is an inevitable
>conclusion of the fixed centre, and the front weight distribution.  needless
>to say the later cars (ur-quattros) have much less of this affliction.
>do other (torsen) audi's understeer?  undoubtedly.  did the ur-quattro?  no,
>not much.

Understeer has more to do with the static and cornering weight distribution 
of the vehicle than the diff attached to it.  Comparing a locked diff to a 
torsen you may have more vs less understeer on initial turn in.  The front 
weight distribution hasn't changed.  Vehicle dynamics of understeer on can be 
addressed with tyres, regardless of diff.  The problem is, this affects the 
operation of the awd system itself.  Different size tyres on a locked front 
to rear, you goes noplace.  Different size tyres on a torsen, you have 
affected the Bias Ratio.  All of these things bad?  Sometimes, but usually 
not, cuz static and braking weight on a quattro is that bad.  Bottom line is 
that unless you have a perfect weight distribution statically and 
dynamically, the same size tyre front and rear is a compromise, by 
definition.  

Maybe Jeff and graydon can post the results of different size tyres on a 
quattro.  I drove graydons setup, it worked really well.  

Scott Justusson