Re: Design flaw in the ASC+T system??

["Gayle, Michael D., LTC, OCLL" <GayleMD@xxxxxxxxxxxxx>]

Recently on the 5-Series board at QualityParts.com, a
thread was discussing the crash of one guy's new E39
528. Apparently, he was doing about 55 mph on the
freeway when his left rear tire went flat. At that
point his car started fishtailing uncontrollably,
resulting in a bad collision with the center divider.
(see http://www.qualityparts.com/boards/5series/messages/2859.html )

Now, I've been in a similar situation (left rear
blowout) but my old Saab 900 was absolutely stable
at 70 mph. Just a bunch of racket from the rear.

One theory out of this was that the ASC of the BMW
misinterpreted the flat tire as a wheel-spin due to
its smaller circumference. From what I've read about
the operation of ASC, I understand that it would 
apply brake to the wheel with the flat, causing 
the car to swerve. It might even oscillate between
brake - release - brake condition as it was trying
to compensate for an imaginary loss of traction,
which would explain the fishtail. Who knows?

As a new E39 owner, I'm quite interested to know
if the ASC does, in fact have a design flaw. Has any
one here had an experience with a rear flat + ASC?
Maybe someone with access to a test facility could
experiment with a smaller diameter tire in back, drive
with ASC off, and then activate it at speed.

Love to know your thoughts or theories on this!
Thanks,

/Jim
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Design flaw . . . bologney!!!  The answer is plain and simple!!
The DRIVER lost control of the car!!  ASC+T modulates the 
throttle and brakes when wheel spin is detected at the rear wheels.
ABS, on the other hand, modulates the brakes to preclude wheel lock-up,
so vehicle control can be maintained in a panic stop or when
low / differing surface friction surfaces exist that could cause loss of
vehicle control.  This means the driver must continue to drive / control /
steer
the car in such situations; the car won't do it all for you.
Was this a '97, '98 or '99 E39?  I am not sure, but don't believe that
BMW started putting on its new cornering braking system that
fully integrates braking action with vehicle attitude when sensors detect an
oversteer condition by comparing wheel rotation until the '99 model year.
As with all technological inovations / tools (not crutches), dependence
on a computer to do the right thing can get one in over their head
or make them so complacent that they have no idea what control
inputs are needed to maintain proper control in an emergency situation
or at high speed.  Did someone say increased numbers of accidents
at Driviers' schools?  We can't forget the basics of car control and vehicle
dynamics.  But, if you never learn; who's fault is it?  Hmmmmm . . . 

Mike Gayle
NCC Membership Chair
Instructor Pilot
Future NCC Driving Instructor

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