[torsen] RE: [urq] When to use Diff Locks? - Kinda long

Glen Dustin Powell gpowell at ennovatenetworks.com
Wed Nov 22 11:16:05 EST 2000


>I know Mr. Powell uses a locked rear in his racing efforts with center
>but historically, Audis race cars run center locked all the time, rear as
>driver preference.  The understeer with rear locked is pretty severe, so is
>tire wear.  That said, if you are putting a bunch of power down (or
>cf, it's the same thing), locking both is the way to fly.  On all my
>quattros, I lock center always, then go after the rear if conditions are
>right, and do this routinely on the fly depending on the conditions coming
>in the windshield.

<My .02
<Scott Justusson

Well, yes and no...

I was running the 84 4KQ in auto-x back in the early 90s and discovered as
have many here have that they understeer like a pig on the typical tight
designed-for-hondas auto-x courses I ran on at the time. I started playing
with tires, pressures and struts to try to dial some of the understeer out
with some success. I also tried running with the C and C/R locked and
neither config worked well in the 4KQ on typical very tight auto-x courses,
understeer was typically more pronounced Vs both open. Then, at the
suggestion of one of the ur-q Pro-Rally guys, I tried swapping the hoses so
I could lock only the R diff. WHAT A DIFFERENCE! Neutral/over-steer
on-demand with that long sought-after RWD-like steer-with-the-throttle
capability - AWESOME! Times dropped and trophies accumulated...

Reverse a few years to running the 85 ur-q in auto-x. With the power and
torque of the ur-q available the ur-q was definitely fastest around the
auto-x course with both C & R locked. Understeer problems were minimal and
throttle helped to rotoate the ur. Never tried R only with the ur. Did take
FTD once for all classes for cars on street tires. GS is not (supposed to
be) the fastest class..... but the ur-q was a monster with the P7Rs Vs other
cars with street tires of the day.

Fast-forward to the last few years of running the 4KQ on the track...
Definitely - locking the C diff makes the car _far_ more stable under heavy
braking and in the transitions we have at NHIS where we go from the
road-course up onto the NASCAR oval and back off the oval onto the
road-course again. When I forgot to lock the C diff I knew immediately my
first time through turn #2 as the car was very twitchy in the transition
onto the oval and immediately locked the C diff and could really feel an
enourmous difference. I cannot provide a datapoint for running on the track
with both C & R locked because I have never bothered to un-do the mod to
enable the C -or- R locked config I have been using. Both locked may well be
the way to go on the track. Perhaps if I ever recover from the fire and get
the car going again I will try it and report back.

On the street - I have observed superior braking stability and improved
stability through standing water, etc, with the C locked. I always use the C
locked in sno/ice/mud and on the highway if it is wet. Improved stability is
unmistakable. Try moving from one lane to another on the highway at speed
when there is a big buildup of sno/ice on the surface - with and without the
C locked. On the issue of both C & R locked on the street - this seems a bit
dangerous IMFO as it is too easy (no ABS here) to lock both rear wheels
under heavy braking possibly resulting in a nasty spin. Once you lock the
rears with the C & R diffs locked you also kill the engine. Depending on
available traction (or lack of same) the wheels and engine may not start
turning again when you finally panic and release the brakes, leaving you
with essentially zero control. You would potentially have to depress the
clutch, re-start the engine with the starter and then very smoothly release
the clutch, while in the correct gear, to get the wheels turning again at
road-speed and to then attempt to regain control, if you are lucky, perhaps,
mebbe. So, I only use both C & R at low speed when really needed in severe
condititions to maintain forward motion and un-lock the rear when speeds
pick up, excatly what the 91 200q20v and other newer cars with t*rs*n C and
locking R diffs. I think this is pretty much in line with both the 4KQ and
ur-q Owner's Manuals.

Happy Thanksgiving!



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