[torsen] Re: [urq] RE: Quattro, Lockers, et al (long)

QSHIPQ at aol.com QSHIPQ at aol.com
Sat Feb 10 13:17:05 EST 2001

In a message dated 2/9/01 4:09:13 PM Central Standard Time, 
Dave.Eaton at clear.net.nz writes:

> actually scott, the audi sae paper bears out bill's experience in low slip
>  conditions.  figure 11 of the sae paper shows that cornering performance in
>  wet conditions is significantly worse with diffs locked than with them 
>  when you consider the increased understeer inevitable when cornering with a
>  centre locker and a rear axle locked, this conclusion obviously makes
>  sense..  i quote.
>  -------------
>  "Fig. 11 shows the deviations with and without differential locks during
>  cornering.  With a surface friction value of µF 0.25 the vehicle's speed
>  very nearly reaches the maximum possible cornering speed.
>  With the centre differential free there is only an insignificant deviation
>  in the control function, and the cornering radius increases by about 2
>  metres.
>  When the centre differential is locked, this causes considerable 
>  resulting in an increase in the cornering radius of about 12 metres.  If
>  both the centre and rear differential locks were engaged, the resulting 
>  slip values could cause the vehicle to leave the corner at a tangent.
>  With high surface friction values, again driving at the maximum cornering
>  speed, no serious loss of stability or performance impairment is observed."

Be careful here, Dave, there is no line in fig 11 for center diff locked, and 
the text only indicates an increase in turning radius.  The mean deviation 
with both diff locked certainly indicates that one can't drive a classical 
turn with better results than just the center locked or open.  I can 
certainly share that fig 11 is somewhat more revised if we are looking at 
ultimate speed thru a corner in low cf conditions.  A bit of the scandinavian 
flick is all that's needed to put the open diff to shame.    A trip to 
steamboat, you won't find any locker driving with center unlocked.  If the 
results in fig.11 were 'really' true, that wouldn't be the case.
>  scott, your large accident at steamboat, was this the result of "the
>  resulting high slip values [which] could cause the vehicle to leave the
>  corner at a tangent" perhaps ;-)

Naw, I don't think so ("large accident"?  I'm laughing at the claim, wait 
till you see the pix;).  My observation was that the difference between 
approaching a low cf turn with diffs unlocked vs diffs locked is a completely 
different car attitude.  Which, would be consistent with fig 11, approaching 
a turn anticipating the diffs locked deviations (scandinavian flick) when 
indeed they were much less (diffs were actually unlocked).  Having the diffs 
engage mid turn from trying to reduce the deviation with lift, only succeeded 
in allowing me the thrill of climbing the bank higher.  

>  bill,  torsen tranny's for the ur-q are not easy to come by.  i've been
>  asked more than once.  the result though is worth the effort.  you're right
>  in that the road testers all had the same conclusions.  btw, i'm not sure
>  how scott can claim authority on the handling of the mb ur-quattro because
>  they never went to the states - but i've owned a wr for 3 years and prefer
>  the 20v easily, sharper handling, more adjustable, better turn-in (and far
>  better engine).  there are a couple of people on this list who have both a
>  wr and an mb in their garage - you could drop them a line, and get the
>  benefit of their (real) comparative experience.

Advocating change before skill is an interesting argument.  There is no 
question in my mind that one of the advantages of torsen is in turn in 
response, that can be felt on any 44 chassis car.  It's the rest of the 
driving scenarios that don't get so comfortable.  Then again, I make my 
living doing swaps, upgrades, service and tweeking, so I'm not really sure 
why I'm arguing the point here (duh).   That sure is a whole lot of money 
spent on a "recommendation".  I might encourage one to spend some more seat 
time in the car with drivers who know the chassis, and find the lockers to be 
a faster and more predictable road and track tool, just like audis factory 
drivers did.  Replacing a torsen does give you the opportunity to add 3 
guages to the center panel too ;).

Scott Justusstuffum
Diff locker duder

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