Re: Torsens and recovery...

[audidudi@mindspring.com (Jeffrey J. Goggin)]

>I've always thought that locking the center diff on dry pavement is a
>no-no. Won't this beat up on the drivetrain? I will be trying
>my hand at autocrossing next month with the QSW, and I don't want to
>trash the driveline (the NTB boys already did that once!!) by
>experimenting with a locked diff on dry pavement if it is going to cause
>any harm. If it is wet, now that's a different story... :-)

Yes, in theory, it has the potential to increase wear on some parts of the
drivetrain.  However, Ferdinand Piech himself has been quoted as saying that
the center diff can be locked at any time without causing any problems ...
personally, I don't worry about it.  The way I drive at autocrosses, the
tires usually aren't hooked up all that well anyway!  :^)  

>How does it cause a harsh ride? I've never heard that before...

At the microscopic level, the road surface is never actually level.  As you
drive, the front and rear wheels are always rotating at slightly different
speeds ... when you hit a bump with the front wheels, they'll turn slightly
faster than the rears because they have to cover more distance going up and
then down over the bump then vice-versa ... with the center diff unlocked,
it will compensate for the continously varying rotational speed differences
in the wheels whereas with it locked, it won't.  The net result is a
slightly harsher ride although the actual degree to which it's harsher
depends upon a lot of other factors, including the brand of tire, its
construction, tread depth, diameter, etc.  In my Ur-Q, for instance, the car
even vibrates more at idle when I've got the center diff locked...

>I have noticed, though, that when the diff is locked (i.e. in the rain),
>it takes more brake pedal effort to stop the car. Why is that? I have
>some theories, but I'd rather first hear your explanation...

Beats me ... I've never noticed this before.

>Thanks for posting it. It makes for interesting and informative reading.
>MUCH better than a Mustang thread, that's for sure...

One point I didn't mention in my Torsen comments last time: One of the
reasons why Torsen-equipped cars will oversteer more readily than non-Torsen
cars is because the rear tires are turning slower in corners than the fronts
... this in turn causes the center diff to send slightly more power to the
rear and less to the front, and the tighter the corner, the larger the
difference.  (This also means that my negative experience using a Torsen
center diff in an autocross situation may NOT reflect its performance at the
higher speeds and larger corner radii typical to an open-track event ...
having never run one of these in my 200q, I don't know if it really makes
any difference or not.  Later this year, however, I may be able to do a
back-to-back comparison since it looks like I'll be buying my girlfriend an
'87 5ktq this afternoon...) 
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   / |      _| o    | \       _| o   Jeffrey Goggin
  /__| | | / | | __ |  | | | / | |   audidudi@mindspring.com
 /   | |_| \_| |    |_/  |_| \_| |   http://people.delphi.com/audidudi
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