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Fwd: Sport q, S1 and rallyes


Dave E. writes:

>remember that there is a 100% torque bias with a locked centre (effectively
>the same as no centre differential at all).  that is you can have 0% torque
>to the front, or 100% to the front, or anthing in between.  ditto with 
>there is no way of "controlling it".  it just happens.

For exactly the length of the wheelbase.  Again, extreme conditions aren't 
how diffs are considered in terms of performance.  I've seen no reviews, nor 
had any btdt on oversteering a quattro into a spin, have you dave?  Given 
that 100% of the torque could be at the rear wheels, isn't that quite 
possible?  How do we explain, even in high power low cf conditions, 
understeer rules locked center diffs under gas or coast?

>quite frankly, according to the drivers, the sport quattro (the precursor to
>the s1) was an absolute pig.  it was based around a centre locker, or
>nothing, and was extremely twitcy.

You may want to read my interview with Stig for more on this.  The S1  and 
the Sport both started with torsens, and ended up with lockers.  
Documentation from audi and the "pre-debut" rag reports clearly show, that 
the variable torque center differential (torsen) was to debut on the Sport.  
Clearly, one can track history of that decision by looking at any sport road 

>the s1 was a considerable improvement and no-one is really sure why.

Obvious to some of us.  Maybe we could believe Stig hisself.

>certainly a lot of effort was put into weight distribution.  

Do you have any documentation of this guess.  I don't.

>you need to
>remember that a locked centre will exacerbate weight distribution by
>splitting torque according to the weight distribution in a static case
>(straight line, no acceleration).  

Not sure why you put this forth.  What is the torque split in straight line 
acceleration?  What does the "static case" have to do with handling during a 
dynamic (acceleration) case?

>certainly a locked centre would make the
>sport quattro a worse handler (more understeer).  remedying the weight
>distribution would make it better.  and an active centre diff would make it
>better again.

Not true according to the test drives, it's a "neutral powerslide" car, in 
both the rallye and road versions.  The problem with weight distribution and 
a locked center, is that even if you were to acheive 50/50 weight 
distribution, you have understeer in a locked center diff.  I argue a fixed 
rear split diff would have been better for the rally cars, and in fact, if 
you look at the S1 competition in the 80's, most went that route, with more 
success than the sport.  An active center diff is just now starting to show 
it's development potential, but a long road still awaits.  Simpler systems in 
the meantime (audi for the next 6years on haldex) are the rule for now.  Not 
necessarily "better" than other awd systems, but the haldex could be said to 
be better than torsen.  Better than a locked center?  Might be an interesting 
test, given they are the same thing, only the latest incorporates ABS, a HUGE 
marketing tool demanded by audi (look at the history of the torsen for this). 
 The older design of Gen 1 has a couple traction and braking advantages 
(locked rear diff) than the edl/tcs systems, but is driver active, not 
computer active.