On Mon, 21 Jun 2004 07:08:11 GMT,
Orienteer wrote:

Bit of a myth that ABS enables a vehicle to stop quicker, in fact it can
have the opposite effect. It's purpose is to enable the vehicle to be
steered while braking hard, which without ABS often results in a skid and
loss of control.

I don't have any figures for it but I suspect that when braking hard
from high speeds (70mph+) ABS may well enable a car to stop quicker.

Some (10+?) years ago there was an artical in SciAm about emergency
stops in cars at motorway speeds and it was suggested that the best bet
for the cars of the time might well be to deliberately skid.

IIRC stopping distances from these sorts of speeds when skidding were
about 20% further than the perfect stop. However, without ABS the
braking is split in a fixed percentage between back and front wheels.
The weight transfer to the front wheels can cause the rear wheels to
lock putting the car into a spin. By deliberately locking all the
wheels the car will stay pretty much in a straight line (motorways
don't tend to have enough camber to be likely to put a skidding car
into a spin.)

ABS eliminates this problem and allows maximum braking on the front
wheels.

But ABS doesn't have to be a good thing. The one time I have skidded
on the motorway I was very grateful for the noise. Picture the scene -
me on empty motorway, slip lane joining. Slow lorry almost at end of
slip lane that would be joining shortly after I had passed. Another
car on sliplane that would be joining about the same time as the
lorry. So I moved from lane 1 to lane 3 in order to give both vehicles
joining room to join without having to adjust their speeds. But the
car doesn't move into lane 2 to pass the lorry but continues into lane
3. Now I should have anticipated this but by the time I realised he
wasn't going to stay in lane 2 I was about level with his rear door
and going maybe 10mph faster. I didn't have time for the horn but my
squealing tyres meant he only came about 2 feet into lane 3.
(Skidding from 70mph to about 45mph leaves a big cloud of smoke!)

Tim.


--
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and there was light.

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