Conference terri::cars_uk

I didn't think stopping distances took wheel locking into
account, so I wouldn't imagine to see that much difference
in dry conditions. In snow and gravel, as the other note 
talks about, the stopping distance is likely to be longer, 
as the brakes can become ineffective and the car just keeps 
on going.

    The new Vauxhall advert which features ABS (which doesn't extole the
    'steering while braking' virtue) seems to imply that ABS gets
    you to a halt better even in a straight line: 
    
    Shot from the drivers eye as he pulls out of the drive on a morning, 
    sees the milkman, jogger, cyclist etc., drives off down the road. Same 
    sequence again implying same next day.  Same sequence again implying 
    same next day.  Same sequence again implying same next day, but this 
    time child runs out into road, car travelling stops in time.

This makes an interesting twist to the argument/debate.

An ABS car will stop as quickly/as well as a non-ABS car provided the same
conditions are met.

i.e. Neither car has its wheels locked/ABS engaged

Up to the point that ABS comes in the braking effectiveness should be the same,
the ABS is only active when a wheel locks. Therefore the debate should follow
the -

 can a car with its wheels locked stop quicker than a car with ABS engaged !

	- direction.......

I think that makes sense !

Andy

	The theory of ABS is that it keeps the wheels at the point of locking. 
That is the ideal, since that is the point of maximum braking efficiency.

	However(!), nothing is perfect as we are well aware (aren't we?) so that
ABS, as implimented on various makes and models of cars, reduces that capability
to a greater or lesser degree.  I believe that some manufacturers models link
the ABS to PAIRS of wheels, instead of each individual wheel - in the interests
of profit (hush ma mouth!), in order that their marketing people can put ABS on
the back of their cars (as well as an "i").  This, of course, does nothing to
help utilise ABS effectively.

	The upshot is, that ABS has the main advantage of - probably - enabling
the driver to retain the ability to steer his car whilst braking heavily which
he/she would NOT be able to do with a "locked up" car.

	So, as we were told on the Defensive Driving Course, NOTHING can
outbrake a locked up wheel in the dry in a straight line!  The locked up car in
a straight line in the dry has the shortest braking distance for that car.

	My present car has ABS, but the only time I'm aware of it is when I'm
braking fairly gently, I occassionally(sp?) feel a pulsating on the brake pedal.
 I can't understand why, but there you go.

				Malcolm.

    Top Gear did something on this. I can't remember the results, I seem to
    remember that with wheels locked ABS increased braking distances in
    most cases, but then I may be wrong!!!
    
    Cheers,
    
    Greg

    .0�UNDER NORMAL CONDITION (IE. ON A NORMAL DRY ROAD), DOES ABS NEED A SHORTER OR
    .0�LONGER DISTANCE TO STOP ?
    
    As indicated in previous replies there should be no or little difference 
    
    IF the road is flat and IF the car is moving straight. 
    
    ABS systems don't like bumps, holes, etc ... that can cause a wheel to 
    lock, causing the brakes to be released resulting in a longer stopping
    distance. This is one of the reasons why certain people don't agree with 
    ABS. Valid argument (in my opinion).

Valid argument indeed, however if you are driving the correct distance behind
the vehicle in front it shouldn't be a problem, pity the xrcdigt brigade have
difficulty with that ;-)

Also, ABS has twice allowed me to get out of an accident, neither of which would
have been caused by tailgating but be demmicks in xrcdigt's pulling out in front
of me, then going oh **** and giving me two fingers because I had to avoid them.
Best ignored cos even if you showed them a video of what they did they wouldn't
see it...

No I'm not holier than thou, I HAVE run into the back of someone....sheepish
grin....wasn't concentrating was I.

    A spinning car with all the wheels locked will stop in the shortest
    distance (but not safest !). This is because a large abount of energy is
    being used up spinning the car.

>    A spinning car with all the wheels locked will stop in the shortest
>    distance (but not safest !).

assuming, that is, that it doesn't roll over...  :/

Chris.

    >>assuming, that is, that it doesn't roll over...  :/
    
    So will a car stop quicker on its roof? :-)
    
    Andy

would that be a polished roof - or not !!

Andy -):

    
    ... Telegraph Poles and Lamp Posts are *very* effective %^), I've had first
    hand experience of both.... given the choice I'd always go for the
    Telegraph Pole now though, they seem to be free - whereas the Lamp Post
    had a hefty price tag attached !
    
    Graham
                                  

    
    
    
    	a) A car with ABS and a Car with non-ABS will break and stop as 
    	   efficiently in the same distance, provided:
    
                1- The road is straigth and dry.
    		2- The car with non-ABS does not lock the wheels.
    	        3- The car with ABS, the ABS does not engage.
     
           Summary: Same distance.
    
        b) Assuming 1- above, and the non-ABS car locks the wheels, then
           The ABS car will stop in shorter distance. This is because the
           speed energy will force the non-ABS car with locked wheels
           to travel longer. Because of the ABS functionality, the ABS car
    	   will reduce the speed energy by the very nature of ABS itself
    	   (ABS - Anti-Lock Bracking System).
    
           Summary: ABS shorter distance.
    
        Toze (glad to have ABS, and re-shapeable (sp?) bumpers during a 
              4 car accident on the M4)
    
    
     
    
    

I was taught (on a skid control training course) to slam on the brakes as 
hard as possible during emergency braking.  The instructor told us not to 
worry about locking the wheels as the objective is to stop in as short a 
distance as possible, ie locked wheels will do this just as effectively 
as ABS.

Of course this is simplistic because the objective might *not* be to stop 
in as short a distance as possible but to (for example) avoid hitting the 
pedestrian who's just walked out into the road.  In such circumstances 
you need controllability, which is what ABS gives you.  

On the course we were taught cadence-braking.  Taking the above scenario, 
the technique was to slam on the brakes as soon as you saw the 
pedestrian, thereby locking up the wheels because this is the fastest way 
to reduce speed.  At the same time steer away from the pedestrian.  The 
car won't alter course (because the wheels are locked and skidding) but 
as soon as you lift off the brakes the wheels will stop skidding, begin 
to turn and steer you away from the pedestrian.  If necessary, repeat in 
order to avoid other obstacles.

It was amazing what could be achieved after only a little practice.  The 
key point being that locking up didn't matter - in fact if you didn't 
lock up the wheels you weren't braking hard enough and would take longer 
to stop overall.  The other point was that in such an emergency situation 
you don't have time to theorise about braking only to the exact point of 
where the wheel begins to lock.

So, ABS or not, go HARD on the brake pedal.

Mike

    .15�I was taught (on a skid control training course) to slam on the brakes as 
    .15�hard as possible during emergency braking.  The instructor told us not to 
    
    This is definitely the thing to do to get the best braking efficiency,
    assuming your car has been running for a while ie the disks and the pads
    are cold. You must get the disk brakes to a high temperature to get
    them work. This takes a fraction of a sec, but it's more > 0.
    
    While racing this is exactly what you should do. But, in order to keep
    control, you'll have to gradually lift off to keep the wheels spinning.
    
    .15�On the course we were taught cadence-braking.  Taking the above scenario, 
    
    Again this is a good idea. The only problem with a 'normal' road car is
    that you will put the car into a swing (nose down, up, down, ...). If
    you turn the wheel (to avoid hitting a pedestrian) the car will
    probably get into a spin (OK). From then on you should LOCK the brakes.
    
    

    A shortcoming I've noticed with ABS is that if the wheels go airbourne
    whilst braking the ABS turns off the brakes. No surprise when you
    consider how it's meant to work etc etc. However a bit of a surprise
    when I was braking at normal speeds (what's normal?) approaching some
    stopped cars at road re-surfacing works. My wheels went airbourne as
    they crested an unusually deep trench running across the road. No front
    brakes for about 1/2 a second!
    
    I stopped in time but I'm glad I wasn't going faster.
    
    Rupert
                              

   Re.14 
    
    
    >>>	a) A car with ABS and a Car with non-ABS will break and stop as 
    >>>	   efficiently in the same distance, provided:
    
    >>>         1- The road is straigth and dry.
    >>>		2- The car with non-ABS does not lock the wheels.
    >>>	        3- The car with ABS, the ABS does not engage.
     
     >>>      Summary: Same distance.
 

	Surely, Toze, your scenario above makes 2- and 3- the same by
definition!  So, the result cannot be different.

	Your supposition of ABS producing a shorter stopping distance on a
straight and dry road is incorrect, under those circumstances, NOTHING can
outbrake a locked up wheel, as the last few notes agree.

				Malcolm.

    .17�    A shortcoming I've noticed with ABS is that if the wheels go airbourne
    .17�    whilst braking the ABS turns off the brakes. No surprise when you
    
    That's what I was refering to in .7 (and that's why I don't like ABS).

If the wheels are air-borne, then they are not helping with braking, so
how does ABS come into that part of the discussion?

As soon as  the wheels contact the ground, then I guess the discussion
starts again, though.

Peter.

    Cadence braking is what ABS does for you, except, with ABS you can
    panic AND steer !!!!
    In accidents I had before I started getting cars with ABS (one or two
    8-), young and stupid with fast car syndrome) I would lock the wheels
    up but still went cannoning into the back of things because I COULD NOT
    STEER!!!!. When your right foot is wedged to the floor on the brake
    pedal through pure fright, very few people actually have the willpower
    to lift it a wee bit to allow you to steer round the thing you are
    sliding towards. Dry or wet roads, it makes no difference to the fact
    that your foot is glued to the floor, and as much as you would like to
    steer to avoid a collision, you can't because you poor little brain is
    having a panic attack!! (It's thinking to itself that if it pushes this
    brake pedal harder, everything will be ok.... WRONG!!)
    
    
    ABS however, allows your poor little brain to continue panicking, while
    also allowing you to steer!! 
    
    
    In my book, that makes it a good thing to have!! Sure, people will, and
    have come up with reasons and situations where ABS may be less
    efficient than a locked wheel, but I doubt whether the parents of the
    poor kid who ran out into the road when you passed his house doing 38
    in a 30 will be particularly interested.
    
    The point I am trying to make is, that for the average punter with
    average driving skills (thats 99% of us) ABS WILL help in avoiding a
    collision. 
    
    I have successfully proven this theory on several occasions in both the
    Astra GTE and my current motor, a Tempra estate .
    
    If you haven't had months of specialised driver training, then like me,
    your foot will try to go through the boards when the smelly stuff hits
    your windscreen!! I just hope the car I've got that day has ABS.
    
    Dave (not-so-young-but-still-stupid-but-without-a-fast-car-now) 8-)
    
                    

    .20�If the wheels are air-borne, then they are not helping with braking, so
    .20�how does ABS come into that part of the discussion?
    
    As indicated in previous replies, when one (or more) wheel(s) locks
    then ABS engages ie RELEASES THE BRAKING ACTION. Then hopefully the
    wheels will start spinning again, BUT, without BRAKES. ABS will sure
    find about that and will start braking again. Depending on your speed
    you'll have wasted some valuable braking distance.
    
    While I was living in Cannes there was a very good test road for ABS.
    It's a (very) steep downhill. At some point, just before getting a
    school zone, the road has been equipped with those miracle bumps that
    remind you to slow down in case you're going too fast. The combination
    of the slope + the cadenced bumps usually mean that an ABS equipped car
    will most probably drive by the school zone without any noticeable
    braking action, although you might be standing on the brake pedal. Any
    non-ABS car will have no problem stopping. 
    
    Finally I should add that, as for every piece of hardware, there are
    good ABS systems, mediocre ABS systems and average ABS system, each
    with a different price and different technology. I understand that
    Bosch are making pretty good ABS systems and expensive ones. Not all
    Fords, Renaults, Fiats, Peugeots, ... are equipped with good ABS
    systems. The ones I have tested never impressed me either as a driver
    or as passenger.

    So does ABS work on a wheel basis or a brake pedal basis? If one wheel
    locks up is it only that wheel which is released or is it the same
    effect as lifting your foot off the brake?
    
    Andy

    .23�    So does ABS work on a wheel basis or a brake pedal basis? If one wheel
    .23�    locks up is it only that wheel which is released or is it the same
    .23�    effect as lifting your foot off the brake?
    
    Many (not all) ABS systems work on the overall system: if the sensors
    show one wheel spinning slower than the other 3 the central computer
    either limits the brake hydraulic pressure or decreases the brake power
    assistance.

re .24;

All ABS systems have at least three different sensors, and most have four.

Each front wheel is independentantly ABS'd, and most systems are independant
on each rear wheel too.

I think (but I'm not sure) that some of the earlier systems paired the
reat wheels together.

Peter.

Re.25
>>>re .24;

>>>All ABS systems have at least three different sensors, and most have four.
>>>Each front wheel is independentantly ABS'd, and most systems are independant
>>>on each rear wheel too.

>>>reat wheels together.

>>>Peter.


	I think you'll find that you're answer doesn't address the question
posed in .23.

	The answer to the question in .23 is that the majority of ABS systems
fitted to "run of the mill" cars, the brakes are released from all 4 wheels.  To
do any more complicated things would be too expensive for us consumers to pay
for at this stage.

				Malcolm.

    .25 and .26 contratict each other.
    
    What type of systems are fitted to most cars ?
    
    Royston

    Most cars will have the cheapest way of doing ABS. After all, as far as
    Ford, Vauxhall, VW etc are concerned ABS is a marketing ploy. If it
    wasn't then it wouldn't say *ABS* is 2 inch high lettering at the rear
    (Just next to the 'i' or 'GL' badge).
    
    Porsche, Ferrari (on the 465) and Honda (NSX) use the Bosch "4th generation"
    ABS system - which is meant to be just about state of the art.
    
    Ford used to use a mechanical ABS system - yuch.
    
    The same goes for traction control systems.
    
    	Rik

    �Ford, Vauxhall, VW etc ... *ABS* is 2 inch high lettering at the rear
    
    I don't believe either Ford or Vauxhall plaster ABS on their cars at
    all.
    
    I seem to recall Citro�n do though.
    
    Royston

    The Cavalier I was behind today (Hi Keith!) had "ABS" written on it.
    Remember ABS has only very recently become standard on Vauxhalls.
    
    I'm pretty sure the same also applies to Ford - though I could be
    wrong.
    
    	Rik

    Rik, my apologies. I stand corrected.
    
    Royston

    My old Cavalier SRI 16V and several others in my office with my old
    employer, all had ABS without a badge. In my experience I have to say I
    would always opt for a car with ABS. It has saved me hitting various
    objects many a time when I was the bog standard AtoB company car racing
    driver.
    				Brian.

    .28�    Porsche, Ferrari (on the 465) and Honda (NSX) use the Bosch "4th generation"
    .28�    ABS system - which is meant to be just about state of the art.
    
    The 'high end' car manufacturers (BMW, Merc ...) use it, mostly coupled
    with traction control. Many traction control systems, when they detect a
    difference in rotational speed on one wheel, reduce the engine power
    until the situation is normal ie all wheels spin at about equal speed.
    
    Only some traction control systems (can't remember which cars have
    that, must be high end BMW and Mercs) will actually apply the wheel brake 
    on the spinning wheel, transferring torque to the opposite wheel (which
    sounds like a very expensive way to build what the TORSEN or any other
    limited slip diff do in simple hw).
    
    (One of) the most advanced ABS systems is available on the latest
    Lancia Integrale. It has 6 (yes SIX) sensors able to detect all sorts
    of funny situations, such as car spinning or executing a barrell roll
    etc   

    Thanks Patrick, it made me laugh.
    
    PACKAGE BODY abs_sensor IS
    
    ...
    
    	IF barrell_roll THEN
    		printf("Agh !");
    	ELSIF ... THEN
    		...
    	END IF;
    ...
    END abs_sensor;

I bet they use C instead of Ada (Ada would be too safe ;-) )

The ABS on my old Clio was the Bosch ABS, and in a review was mean't to be
superior to that offered on the Fiesta.

I only ever felt it work once (and that was intentional testing
on a wet day), and it's action was subtle and effective.

A Calibra I was in once, made a hell of a racket and seemed to dive for
the ground when the ABS was working!

Mark.

    Rule: ask for a test before you buy, find a really terrible road,
    downhill, potholes, rainy day, bends, and go ... bang on the brakes.
    
    If still alive please enter your comments here.

    I'm confused now. I've got a BMW 318is and I'm pretty sure that it'll
    only "un-lock" the wheel that has locked. The other wheel continues to
    be braked normally. I've noticed this when pulling to the side of a
    muddy lane to let oncoming traffic pass. The wheel on the mud judders
    with the ABS but the car is still slowing down normally.
    
    The only thing that throws it is bumpy, rutted roads. Although I could
    get addicted to that adrenalin high when you realise the brakes have
    turned themselves off for about 1/4 second!
    
    Rupert
    
    
    
    

Re.27

  >>>  .25 and .26 contratict each other.
    
 >>>   What type of systems are fitted to most cars ?
    
>>>    Royston


	Not really a contradiction Royston - .25 is refering to the number of
sensors, whilst .26 is refering to the number of wheels at which the brakes are
released when the ABS system detects that one wheel is going slower than the
others.

Re.29

>>>    I seem to recall Citro�n do though.
    
>>>    Royston

	I think that the BX may have done, but the standard fitting ABS on my
Xantia isn't proclaimed anywhere on the Car.

				Malcolm.

    I am coming into this note a little late but would like to give my two
    pneth  :
    
    My chosen means of transport is by motorcycle. On a bike NOT locking
    the front wheel is the MOST important thing while braking.
    
    ABS is available on some makes - I think BMW first tried it - and there
    is mixed feeling on braking efficiency. ABS on a bike is not about
    being able to steer while braking it is purely about not locking that
    front wheel.
    
    The whole effectiveness of whether you stop quicker depends on how you
    use the brake lever. For example  :
    
    Two bikes riding side by side - same model, same speed - one has ABS
    the other does not.
    
    The non-ABS guy (who is a non human super robot!) pulls on
    the front brake to the exact point where the brakes are working to
    their maximum efficiency before they would lock the front wheel. He
    stops in the minimum distance possible.
    
    At the same time the ABS guy (who is like the rest of the population,
    and knows he is protected by his ABS) yanks on the lever as hard as he
    can. 
    
    Repeatedly the braking reaches its most efficient point then passes it
    and the ABS releases the brake to stop a skid. The ABS then re-applies
    the brake until the maximun point is reached and passed and then
    releases it again.
    
    The first bike was at the maximum braking point all the time (don't forget
    this rider is not human!) the ABS rider's bike reached the point then
    released several times - he cannot of stopped quicker.
    
    Admittedly you have to be fu*$ing good to be like the non-ABS rider and
    there aren't many people that good except the pros. The ABS rider
    doesn't need to be that good 'cos hs's got a machine to fu@!ing good
    for him. All I'm answering is the original question - Do you stop
    quicker.
    
    Cheers - Rich 

But surely if you nearside wheels skid and so ABS becomes
effective, whilst the offside wheels brake normally, you would
spin round in a circle as the brakes would not be applied
equally across both sides of the car. OK, you may not spin,
but I would imagine the car would drift towards the right.

Are you sure the BMW system works in this way?

    ahhhh...
    
    I have first hand experience of ABS on a Cavalier SRi 16v
    Granted I was probably going to fast (in retrospect) but had
    the car not had ABS I almost certainly would have stopped in time
    (before stopping in the side of an Astra!) The road was wet, very
    broken with a particularly large trench just before a junction,
    also there was some weight in the back. I hit the trench, stood on 
    the brakes and as the rear wheels jumped out of it the brakes 
    "cadenced" for a few seconds giving the effect of NO BRAKES
    The car slewed forward for several yards more than it would have done
    without ABS. As the Vauxhall sytem reduces brake effect when ANY one
    wheel lifts, this results in a longer stopping distance on uneven
    ground in wet or dry, though I havn't noticed it as a prob in the dry.
    On the other hand my wife locked the front wheels of a Citroen BX
    in the wet, and went off the road (steep downhill adverse camber)
    and with ABS would have retained steering control and stayed on the
    road. Any BX drivers will be aware of the "binary "nature of said
    brakes. 
    So whether ABS is good or bad seems to depend very much on your 
    preferences. personally I don't like it.
    
    Matt

    ABS is not about stopping quicker....it *is* about maintaining control
    of the car under questionable road surface conditions.  ABS will
    not replace a good dose of common sense.....it *will* assist in
    accident avoidance presuming the driver has not been doing something
    stupid like driving too fast for the conditions.
    
    Brian
    
    Oh, and ABS is very effective on glare ice....been there, done that in
    a Mercedes...I got stopped. The guy behind me locked his wheels,
    stalled his engine and had *no control* what-so-ever as he slid into the
    back of my car.  The guy in front of me had slid through the "T"
    intersection and ended up in the ditch on the other side.
     

    ref .40
    
    I checked with BMW in Bracknell and their technical dept said that each
    caliper is individually controlled. I assume that it works so well that
    the little grip afforded by mud contributes to keeping the car pointing
    straight. Also I'm probably sub-consciously correcting any yaw effect
    with the steering.
    
    As people seem to be saying, there are ABS systems and there are ABS
    systems. 
    
    Rupert

re .37 & .40

I've had exactly the same experience in muddy lanes when pulling over to 
let another car pass.  The ABS does its stuff on the nearside wheels but 
I've not noticed any tendency to pull to one side as a result (this is in 
a Saab 9000).

I've also done the same in a non-ABS car and, frankly, there's little 
discernable difference except that the nearside wheel does lock as it 
slips on the mud.  This was also a Saab 9000 so is a good comparison (not 
sure what the conclusion is though - ABS makes no practical difference ?)

Mike

    re-1
    
    Yes, I also have a lot of experience of pulling over sharply on muddy
    lanes.  My astra doesn't have ABS, and seems to randomly select which
    direction it actually goes in.  Tha Cavalier does have ABS however, and
    I've not had any problems at all with stopping or steering.  So, it
    gets my vote.
    
    Mikef 

I had to stop in a hurry without ABS, and burned flat spots on the bottom of 
the tyres, obviously skidded, and nearly killed a motorcyclist driving 
without lights down a dark country road......

I had to stop short in a car with ABS on a wet, greasy country road and was 
frankly amazed how safely and quickly the car stopped (accident avoided).  I 
am a convert.

There are times when we all get caught out, and I for one am glad of the 
safety net of ABS, as I am glad of seat belts, and would like airbags as 
well, just for the moments when that one slip occurs......

	Tim

    I can testify to ABS extending the stopping distance if activated on
    normal dry road conditions. My Calibra had a faulty ABS system for
    several months, and the ABS activated when I was slowing down. Once I
    got down to about 5mph, the ABS would turn itself on - often causing me
    to drift out on to busy junctions, or to hit the car in front of me. 
    I would say that in these circumstances, they double the stopping distance.
    
    Not a nice feeling.  Vauxhall fixed the problem in the end - but it
    took 6 months of hassle.
    
    Cheers
    
    John Scott 

    I can testify to conventional brakes extending the stopping
    distance. I had a white mini 1000 (round about 1974 it was) and all the
    brake fluid ran out through a seized/burst brake cylinder. The road
    conditions were good but it still took some time before there was any
    noticeable slowing down. Eventually, more out of frustration, I used
    the handbrake which was marginally quicker than rubbing my foot on the
    road. A very nice garage fixed it on a Sunday afternoon.
    Really John I'm not sure faulty anything can be used as proof. Also
    your patience amazes me. If I was drifting out at junctions and running
    into other vehicles then I wouldn't be driving the car for very long.
    
    Andrew