The answer to your question depends on the car in question. A basic
ABS system senses whether you are locking up one or more wheels during
braking and cuts brake pressure to those wheels. This is done using a
feedback loop, checking X number of times per second. X has increased
over the years.
With basic ABS, you should get on the brakes quickly but smoothly (so
that you can get some weight transferred to the front of the car
before you hit peak braking force) and then hold the pedal down as far
as you can. The results will be as good or better than threshold
braking on a clean dry surface.
If you get onto the grit, sand, pebbles, or mud along the edge of the
course, then ABS may trigger prematurely and it will be annoying.
It's possible that you could stop faster just by locking up the brakes
if you get into the marbles.
I've heard stories about modern ABS systems that seem to have been
designed under the assumption that the driver is an idiot. They have
pre-programmed responses to how the controls are activated. I've
heard of cars where if you engage ABS and then suddenly lift your foot
off the brake, the system apparently thinks that the ABS vibration
spooked you and continues to apply full braking since you obviously
wanted to stop. Right?
As ABS becomes integrated with vehicle stability programs, I think
you'll see a lot more systems which try to outsmart the driver, with
approximately the same results as the computer software which is
programmed to do what it thinks you want it to do, despite your having
asked it to do something else...
On Mon, Mar 24, 2003 at 04:18:12PM -0800, Matthew Rehrer wrote:
> All-
>
> This questions may be too generic to answer definitively
> however that just shows how badly I need opinions.
>
> If I have a car with ABS that cannot be disabled is it
> reasonable for me to assume that the car will stop in
> the shortest distance possible if I simply slam on the
> brakes (thereby engaging ABS)?
>
> If this is not so then what sort of penalties are likely
> in this scenario? In other words does a good ABS system
> get within 10-20% of ideal non-assisted braking? How
> about in the wet (where yesterday I had abysmal braking
> most likely due to driver errors)?
>
> Also if engaging the ABS is evil what techniques can be
> used to avoid the dreaded HAL9000 intervention?
>
> Thanks for your thoughts
>
> Matthew
--
john@idsfa.net John Stimson
http://www.idsfa.net/~john/ HMC Physics '94
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