[torsen] Quattro, Lockers, et al (long)

QSHIPQ at aol.com QSHIPQ at aol.com
Fri Feb 9 08:30:04 EST 2001

Bill Elliott wrote:

>Anyway, I recently purchased the Dec 82 edition of Car and Driver where
>they pit the then-new UrQ against a Surburban, Eagle, SAAB 900, etc.
(>This is a pitiful piece of biased journalism... the goal beforehand
>seemed to be to prove that the UrQ simply wasn't worth $35,000... so it
>competed on high performance summer tires against all-season and
>all-terrain tires on the snow and ice. No tarmac tests were run. The
>>judgement was it was a "good, but not great" snow car.)

Hehe, that's what I tell anyone that asks too, but still offer the ride ;)

>But they did measure lateral G's on an ice-covered skidpad and (not
>surprisingly considering the tires) the UrQ was the lowest of the bunch.
>But it was even lower than the tires would account for... and
>significantly lower still with the diffs locked.

Well, it's a front heavy car, so any measure of "skidpad" performance I would 
expect it not to do well.  That said, the driving style of the quattro 
requires that one go "in like a lamb, out like a lion", which means the 
quattro advantage is accelerating out of a turn, not carrying speed thru it 
with sheer g forces.   This applies from ice to tarmac. 

> In my recent ice-racing education, I've come to accept that I simply
>have less lateral grip than the 2wd cars and even less with the diffs
>locked. (My wife refuses to drive a quattro when the going gets slick
>because of this issue.. she says she's lots more stable in a FWD.)

Hmm, had this discussion many times...  In FWD, you have the engine over the 
drive wheels, and at low speeds this can give the "extra" traction in 
slippery conditions.  FWD also has the advantage of Lift Throttle Oversteer 
(LTO) which is easier to modulate for the less advanced driver than U or more 
U.  However, simple physics would indicate that as speed rises quattro 
advantage gets better, because the front wheels are only getting 50% of the 
drive torque, which means they have an inherent better steering and tractive 

>Now this brings me to the next issue... on the ice track, running with
>the center diff locked seems to be the fastest under most all
>circumstances due to the ability to accelerate on the straights, but
>significantly slows me down through tight esses.  The guys with the
>torsen cars seem to have the best of both worlds... acceleration and
>more lateral grip.  Am I missing something here or do I just not know
>how to drive my locker correctly? (I'm not yet smooth enough to lock and
>unlock at will on the course.)

ALL performance driving in a gen 1 quattro should be with the center diff 
locked.  Dave E's SAE 880321 Fig 12 shows that even in the worst conditions 
(mixed cf) the center diff locked will give better steering and braking 
performance than the center diff unlocked.  I suggest you come to any quattro 
club event (steamboat and/or others) and take a ride with one of the better 
locker drivers.  Looking only at the above, I would say that you need some 
instruction on how to drive a Gen 1 fast.  They do understeer, but it's more 
predictable at the limit than the torsen car, it should be used in tight 
corners (unlocking the rear, not the front), and your driving style should be 
modified according to the Buffum technique.  The guys in the torsen cars 
*don't* have better acceleration and better lateral grip, for if they did, 
audi would have used it more in racing.  The biggest issue with the torsen is 
slip angle differences across the center axle causing a torque shift mid 
turn, which requires a corrective input from the driver.  Somewhat oxymoronic 
IMO, since if you are at the limit of adhesion, you have no ability for 
"corrective" input, certainly not to make you 'faster'.  Even today, with the 
Motorola Cup car 00S4 chassis, the diffs are locked, in a car that was 
designed for a torsen.  That should tell you a lot.

All that said, the torsen is an effective awd tool, it just has some inherent 
flaws in it's application when driving at higher speeds.  I've watched 2 
drivers that have modified their driving style to make the torsen work well, 
one at steamboat, one on the dry track.  However, my assessment of both 
drivers, is that the ultimate commitment of the chassis during all phases of 
the turn is really high (nothing I'd want to teach), and certainly not the 
fastest way around any course.  So to change your locker to a torsen, would 
be premature, Bill.  Get instruction first, these cars are phenomenally fast 
and predictable, and were designed for the lockers, not the torsen.

>And finally... assuming I'm going to need a clutch in the near future I
>sure as heck am not going to pull the engine until I need one) how
>difficult would it be to swap in a later gearbox with torsen? Is this a
>bolt-in or a major fabrication job? And would the result be close to the
>MB UrQ? (Everyone that has driven both seems to FAR prefer the dynamics
>of the MB over the WR/WX... or am I wrong here as well?)

The swap to a torsen requires that the tail section of the trans be modified 
to take the torsen housing which is slightly longer than the locker, so it 
will also require a driveshaft from a 80/90q chassis car (or just the whole 
trans might be cheaper).  The reasong the MB appears to be "preferred" is the 
turn in reponse of a torsen car is inherently quicker than that of a locker.  
However, the locker car is predictable always in terms of it's performance, 
the torsen can shift up to 56% of the applied torque between axles based on a 
whole matrix of variables while in the turn.  That is always in the back of 
my mind when I'm playing with any torsen car.  

Bill, I highly suggest you go to Steamboat before you commit changing 
anything in your quattro.  You have 30 cars to choose from, and what you find 
pretty quickly, is that the lockers rule the track, in fun, predictability 
and time.  Interesting to note too that no torsen equipped car has ever won 
the SCCA Rallycross at the Steamboat venue (and that's 250+ cars competing 
over the years, of all makes).  

>I don't really want to get the whole torsen thread started again (but I
>do suscribe to that list for the interesting reading) but since Scott's
>brought up the subject, I figured I'd ask my questions.

Hopefully I haven't rehashed too much, and sent this only to the relevent 
lists (as one has so eloquently prosed I should).  All the above said Bill, 
the torsen is easier to drive, and is much more transparent awd for anyone 
driving below the 7/10ths level.  The reason it was used by audi was no 
action required by driver, and abs enabled was (and still is) a huge 
marketing tool in awd driving.  So the question you need to ask yourself is:  
Is it you that wants to learn the car, or do you want to change the car (and 
in your case, you own 3 lockers, to really get good at torsen, you should be 
driving just torsens, switching back and forth isn't going to help you).  20 
years of performance driving, IMO, I'd take predictability over convenience 



Scott Justusson
all lockers
'87 5ktqw
'87 4Runner turbo
'84 Urq
'83 Urq

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