Locked Diff = Twichy/Oversteer?

[Frank de Kat <fdekat@sentex.net>]

At 01:51 PM 23/09/99 EDT, QSHIPQ@aol.com wrote:

Not that what I'm saying has anything to do with the 'spider bite' thing..
(And ONLY applies to my personal experience in a 4000q..)

>Please provide ANY 
>documentation supporting a locked diff in a quattro, throttle oversteering 
>during a turn.  Most audi racers, and everyone here with btdt would be in
awe 
>of *any* support to this claim in ANY locker chassis.  

I submit this thought:

When the center diff is locked, the front and rear axles are 'forced' to
follow the same average distance. 

When turning a corner on pavement, this 'forcing' is manifested as the car
feeling harder to turn (Wanting to stay going straight ahead, due to the
lack of front/read differential action).
This makes the car feel vey 'heavy', as the distance 'differances' are
absorbed by driveline twist, or wheel hop in extreme cases.

However..
When on gravel, the action is a little different. The same 'forcing front &
rear to travel the same distance' action is there, but the traction level
is less. This causes the 'axel windup' to be dissipated by the tires
sliding a bit, due to the lower traction. This dissipation of the extra
distance makes the car feel looser, and tends to make it feel much more
like a rear drive car. I still think it's inherently oversteering then, but
give the car a good 'flick', and the back end hangs out really well.

>'ve been to Steamboat 
>for 5 years in a row now, not once have I seen nor heard of any locked 
>quattro driver talk about "oversteering" into a spin, with either the center 
>locked and or center/rear locked.
My previous comment does not seem to go this far. Once a certain angle of
slide is reached, the front wheels seem to come into effect, and start
pulling the car, preventing a major spin, such as a rear drive would do. In
fact, on low friction surfaces, I've managed to get the car at an angle to
the road, but going straight *down* the road. It looks really weird..
However, locking *both* diffs hauls the car back into understeering mode,
where the locked rear goes a long way to resisting any turning action. Like
the owner's manual sugggests "Use when you are stuck, or imminent danger of
being stuck". Works great then though!

>>as for the handling of the sport quattro (with locked centre).  what do you
>>think contributed to it's twitchiness?  perhaps we should say that because
>>the sport q was very twitchy with a locked centre, all quattro's with a
>>locked centre's are twitchy?
COuld we not? If there is no way to account for the different distances the
 front & rear wheels travel, what happens?

>Love to hear from any locked diff driver about the WOT/LTO oversteer with
the 
>center diff locked.
Well.. That's how I like it, rear end out, oversteering all the way, when
out having 'fun' driving on loose surface roads..

>Then we'll get a conference call with John Buffum, "Hey, John, in your
book, here's what you >shoulda done..."
I don't know.. Does it make sense asking someone who has probably crashed
more Audis than anyone else in NorthAmerica how it should be done?   (And
that's got a ;=)  at the end!)


Regards!


Frank de Kat 
fdekat@sentex.net   
Dundas, Ontario, Canada

http://www.sentex.net/~fdekat
To see "The Rally Pictures"