Differential Locking - a Racing View of low traction conditions

[PDQSHIP@aol.com]

STEAMBOAT SPRINGS, CO  Winter Driving School, Multi-plane track 8 turns, 2
straights, 100,000 gallons of water, lots of snow......  Car: 5ktq, hi - hp,
coupla mods, boost at 11-12psi, 91 octane premium,  extra oil.....  Tires:
P210's 205/60 on 15 X 7 rims
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.

*  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.

The speeds that I attained during this event were 70-85mph on the long
straight (1-8), 60mph on the short straight (7-6)....  

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.  

Bizzacks.....   Another post, let's suffice it to say, my big 5ktq with
P210's was hardly outgunned....  If anyone wants more nerdy stuff like the
line vs locks, I would be happy to share....  HTH those of you with the diff
lock questions this winter


Scott
Skipper - PDQSHIP