> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Dave Tweed
> Sent: 23 November 2009 16:57
> To: piclist@mit.edu
> Subject: Re: [OT] What happens when you get rear-ended
> 
> Michael Rigby-Jones wrote:
> 
> > To correct a locked wheel without such a system, a driver would have
to
> > reduce braking effort to all four wheels, which increases overall
> > stopping distance.  Since the maximum grip available from any
particular
> > wheel will vary, to prevent (rather than correct) locking a driver
will
> > have to reduce the total braking effort to the level of the wheel
with
> > the lowest grip.  Having a higher braking effort to 3 wheels and
> > allowing the ABS to cope with the other one will very likely give
> > shorter stopping distances.
> 
> That's a specious argument if I've ever heard one.
> 
> Unless you're already FUBAR (skidding) by the time you hit the brakes,
the
> wheels tend to follow one another on each side of the car. In other
words,
> it's extremely difficult to be in a situation in which you have just
one
> wheel with poor traction when you need ABS.

This is not really true; whilst the wheels on any given side will
naturally tend to run over the same bit of road, they aren't loaded in
the same way (either statically or dynamically) so their behaviour can
vary.  I have had a single wheel lock up on several occasions in the
past when driving pre-ABS cars, when you have to make the decision to
either stick with it and try to maintain some level of control (a single
front wheel lock greatly reduces steering ability), or release the pedal
and waste a significant amount of stopping distance.  A decent ABS would
have allowed me to keep the pedal pressed whilst maintaining control and
not extending stopping distance at all.  The early systems would have
allowed steering control to maintain, but likely at the expense of
overall stopping distance since braking effort would have been reduced
on either all, or at least a pair of wheels.

Regards

Mike

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