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Diff Locking II - a racing view of low traction conditions



Last year I wrote this: (>> = Edited/updated for '97)

Subj:	Differential Locking - a Racing View of low traction conditions
Date:	96-02-07 16:20:19 EST
From:	PDQSHIP
To:	quattro@coimbra.ans.net

STEAMBOAT SPRINGS, CO  Winter Driving School, Multi-plane track 8 turns, 2
straights, 100,000 gallons of water, lots of snow......  TEMPS = -30 to
-10Car: 5ktq, hi - hp,
coupla mods, boost at 11-12psi, 91 octane premium,  extra oil.....  Tires:
P210's 205/60 on 15 X 7 rims
>>  Gislaved Nordfrost M&S 205/55 on 16X7.5,  TEMPS = +30 to +10
After trying various methods of Diff Locking at the Steamboat Winter Driving
School, I will share the following guildlines for the fastest q driving on
slippery surfaces......

*  The center Diff Lock, although makes for inherent understeer, is plenty
controlable on ice and snow, and traction and control is miles ahead of open
diff operation, ABS was not enough of an offsetting factor for control or
braking.
>> Still a valid statement this year

*  The Rear DIFF LOCK ON created WAY too much understeer, and generally
helped only to launch the car out of the hole, but generally sucked if you
left it on for the whole track.  The technique I used was to get halfway into
the turn and then lock the rears, do a first second shift then disengage the
rear BEFORE TURNING, and since it executes un/lock under no-load conditions,
a quick blip of the throttle right before braking proved effective in
dictating the release of the rear diff.....   I did not use Rear DIFF LOCK
when exiting turn 1or the loop on 8, but did use it every other turn at this
track.  I tried the diff lock coming out of the sweeper on 2 (to1 to 8, CCW)
and found the understeer too much, and basically, there was no gain in time
or speed having it engaged on that straight.   I would tend to bounce the car
off the snowbank on the exit of turn 1 anyway, and with DIFF LOCK ON, my
bounce became a slam, and there was no speed gain......  8 was a 270 circle,
that was very tight, and again, no gain in speed and great loss of control by
LOCK ON.
>>  Interesting to note, this year, I ran DIFF LOCKS ON (CW) from 8 to 3,
then off till center of 3, ON mid 3, 4 OFF at turn in of 5, ON mid 5 thru 8.
 CCW = ON 1-entrance to 7, then OFF till mid 7, ON 7 thru entrance to 6, then
OFF 6 thru entrance to 5, ON 5,4 thru entrance to 3, OFF to mid 3, then ON
3,2, entrance to 1 OFF, ON - mid 1....  The track was slicker this year (more
ice), which probably accounts for the gain in control over the understeer the
rear lock on created...

The speeds that I attained during this event were 70-85mph on the long
straight (1-8), 60mph on the short straight (7-6)....  
>  75 & 45 respectively...  Less boost the primary problem....
SUMMARY:

The use of Center Diff Lock in slippery conditions offsets any lack of ABS
for doing such.  The use of the REAR DIFF LOCK all the time would give you
understeer beyond any gains in traction, and a true time loss of overall
speed.  I was not aware of any gains in compression braking with rear lock
on, so I discount that traction argument.  The trick is to know when the REAR
LOCK should be dis/engaged, that is, coming out of a real slow corner where
maximum Traction is desired over the MASSIVE understeer this manuever
creates.  The difference was amazing......  Some comfort in the use of
"another" control is needed to Lock and Unlock the rears, but great
advantages in control were the benefits......   BTW, I did not use handbrake
turns anywhere on the track, and did little if any (taught) brake pumping,
all braking was threshold/skid type.  
>>  Ditto.  I could run more of the track this year with the REAR DIFF ON,
but attribute that to the icey conditions being more forgiving of the Rear
diff lox on.  Mid turn locking for exiting no doubt was the trick, and a blip
of the throttle made the disengage into a turn most predictable.  Forgetting
to unlock immediately put you into the icey parts of the track, by definition
the slowest way around.  Ned was actually running his diffs open for turn in,
tried with little luck to help teach the locking trix.  Very fast considering
the technique he used.

End of Report.

Scott 
QSHIPQ@aol.com