Since the rears only contribute 20% or less of total braking power it is
real doubtful you would feel it when it engaged the ABS.
My 95 Conversion has 4wheel ABS and you can't feel it when the rear
Think about the typical plumbing of the rear brake lines. A single
line runs to the rear axle where it connects to a block that then
distributes the pressure to both wheels. Only need one sensor, only
one line to pulse, that sensor is in the tailshaft of the
And before ABS, the plumbing to the right and left front brakes were
also on the same line, distributing the same pressure to each front
wheel. They changed the front, why not the rear also? When towing and
adding 750 pounds of tongue weight to the rear (add in the leverage
factor and it's more than an extra 750 pounds to the rear wheels), they
would be capable of more than the normal 20% braking. Why not use it?
I know, I'm just being anal. They aren't going to design anything
different for the few who use the vehicle for towing.
Ahh, it is not a myth. I DO understand physics. It is your position
which is the myth.
1. ABS is designed to maximize breaking without locking up the wheels.
2. The MAIN reason #1 above is important is because skids result in
longer stopping distances under most common road conditions. In some
situations, such as built up "damning" of snow or on some gravel
surfaces, some skidding results in the shorter stopping distance.
3. Steering during braking, while still important, is a SECONDARY goal
4. #2 above is supported by the underlying concept in physics called
starting/standing coefficient of friction vs. sliding coefficient of
On a typical rubber on pavement or blacktop situation, the sliding
coefficient of friction is less powerful than the starting
coefficient. In a skid, the sliding coefficient of friction is in
play. When the maximum amount of resistance is applied against the
wheel rolling (braking pressure just short of resulting in a lockup),
then it is the starting/standing coefficient of friction in play where
the rubber meets the road. Since it is basically impossible to
precisely apply the maximum brake pressure just short of a lockup, ABS
does the next best thing it can. And that is to very quickly back the
braking pressure off a little. Then it almost immediately allows the
braking pressure to climb again. As soon as it senses that lockup is
again starting, it backs the pressure off a little very briefly. This
is why there is a rapid pulsating effect when ABS kicks on a long hard
braking. Essentially, it results in the braking pressure fluctuating
a little under to a little over the optimum force.
Most folks just don't understand this because some of the forces at
work are outside of their normal realm of observation. I have argued
this at length with others on usenet. In addition to some limited
background in physics, I also researched that shorter stopping
distances are the primary goal of ABS and sited my sources. The
opposition couldn't find a single shred of credible research to back
But anyway, for something new to try and make the point easier to
understand, I came up with a new analogy. Let us for the sake of
argument, grossly exaggerate the difference between the values of
starting and sliding coefficients of friction (of tire compounds on
typical roadways). Let us say the sliding coefficient on the car is
small but not zero. This would mean the car with locked up wheels
would skid a LONG way before finally coming to a stop. Zero value
would result in never coming to a stop (barring air resistance or
Okay, on the other side, let us say that the starting/standing
coefficient is infinite. This means that the car will go only exactly
as fast as the wheels turn. Not a hair more or less, but EXACTLY the
rate as the wheels turn. And the rate the wheels turn then, would be
a function of force of inertia (speed and mass of car) pitted against
resistance force of brake shoes or pads. If the brakes were powerful
enough to resist the inertial force up in 2 seconds, then that car
would be stopped in 2 seconds flat because the infinite friction of
the tires would not allow a skid. Basically, you are able to employ
100% of the braking force towards overcoming momentum.
In the real world, if the wheels lock up, you are ONLY getting the
resistance of sliding friction, which is not as strong as
starting/standing friction and the braking system in MOST cases.
There ARE exceptions to this. But my main original point still
stands, that ABS results in shorter stopping distances in most
conditions, for most drivers most of the time. Studies and tests bear
this out as well.
I think a really really good driver could be nearly as efficient as
ABS under the conditions that ABS works best, and that same driver
could OUTPERFORM ABS by a good bit in those situations where ABS works
least well. So, if you are real good AND do not ever panic, you
probably are better off without ABS. Also true of you drive a lot on
gravel roads or slippery roads with a layer of snow on them. Because
then, the starting/standing coefficient of friction actually drops
lower than the sliding coefficient is when figuring in the damning
effect of pushing snow or gravel.
This is where your problem is, this was not the goal of ABS. ABS was
designed to prevent the wheels from locking so you can maintain steering,
maximizing braking was not a design goal and simply cannot be done with
ABS. The "better braking" is what people are starting to think and is
resulting in more dangerous drivers who will over drive the situatuion.
Yes, skids do but proper braking is applying enough pressure to stop without
skidding. The untrained driver will simply push the pedal as hard as they
can and cause a skid which is where ABS does help, but anyone who has
actually tried to learn how to drive can easily feel the right amount of
pressure. But as ABS becomes more standard it becomes harder to learn this
feel because a slight wheel hop at that threashold will trigger the ABS
(which is my main problem with it) and result in loss of braking power as
the ABS releases pressure. I have felt it many times as one wheel touches
a crack in the pavement the ABS system will detect a slight change in wheel
speed and release the pressure causing the vehicle to jump forward and then
attempts to build pressure back up to the point where I already had it.
ABS would work in a perfect world where there are no pavement cracks and
patches or potholes but I never drive on perfect roads. Unless ABS can
have some way to sense road conditions there isn't any way it could ever
decrease stopping distances. Sure it will in a lab test because they have
perfectly paved roads.
Steering was the whole reason ABS was designed/invented, go back and do the
research and look at the history (i think it was Volvo that first put in
into production) and the design goals and reasons they designed it.
Yes and this is the problem. I'm a very uncoordinated person and certainly
not the best driver in the world but I can hold a brake at that correct
amount of pressure and if someone such as I can do it then anyone else can
do it easily too. I am well below average in eye-hand coordination, could
never play sports or video games so that means it only takes below average
coordination to beat ABS. Each time the ABS system releases the pressure
the stopping distance increases when compared to a person holding the
brakes at the maximum pressure point. The old ABS system in the Chrysler
we had pulsed maybe once a second, the current GM I have does 3-4 times a
second. Many people who believe ABS can stop better will claim it pulses
millions of times a second therefore it can react faster than a human but
while it may read the sensors that fast the mechanicle parts in the brake
system can't react that fast. Think about the old rusty car pulling away
from a stop and you hear the brakes squeak a couple wheel revolutions that
old car ABS wouldn't even work because it take a good couple seconds for
the pads to release pressure :) But even a modern good working system
won't release in a microsecond which would be required for millions of
pulses per second on the brake system. So a few times a second seems to be
the average and each time it backs off the pressure your extending the
distance, so the 3-4 times a second you slightly extend the stopping
distance by not breaking at maximum adds up.
I don't know who you opposition is and what research you have done, but the
goal of abs was steering control. There have even bee documentaries on the
discovery channel/tlc/history channel when they go into the history of cars
and such where they talk about steering control. Traction control has
become a secondary goal of ABS systems though.
- I do not have a problem.
- Shorter stopping distance was the primary goal of ABS.
- Maximizing breaking under many circumstances is done better than a
human could do it.
- It is not easy to apply EXACTLY the maximum brake pressure short of
a lockup. Scientific tests prove this, because ABS results in shorter
stopping distances. If it were so easy for people to outperform the
ABS, professional test drivers would do BETTER without ABS engaged.
But they do not. Their stopping distances are shorter with ABS
Wheel hops are not the norm. They certainly are not rare to be sure,
but in total, most stops are achieved shorter with ABS. You can bring
up all kinds of perimeter variables, but it doesn't change that most
of the time ABS performs better than the driver would/could.
Well, just as the "lab" supposedly has perfectly smooth roads, you
seem to drive on nothing but bomb crater alley every waking moment. I
think I'll just leave it at that. Reasonable people can make of it
what they will.
Not according to everything I have found on the subject. Shorter
stopping distance is numero uno in what I have looked up. Shorter
stopping distance was always listed 1st and/or more prominently than
maintaining steering. But you know what, it really doesn't make much
difference. I was rebutting the notion that shorter stopping distance
with ABS is a "myth".
What you are probably doing is applying a braking force that is not
causing a lock up, but yet is not as much pressure as could be applied
within the threshold. I have anecdotal evidence of my own as well,
but I value controlled testing more than I do what you or I have
experienced just on our own. That being said, here is my 2 cent
anecdote. I am fairly well coordinated person; probably above average
judging by some things. I also can usually stay in control under
stress. I have been "battle tested" so to speak. But anyway, there
have been a couple of times where I mashed the brake pedal down
because of a possible / probable imminent collision. The ABS was
activated before I had time to even fully understand what was
happening in the cerebrum. "Fight or flight" was ALREADY engaged.
Thank God so was the ABS. What I did realize, was that I would have
probably locked up the wheels, at least for maybe a second or part of
one, had I not had ABS. In less than another second there would have
been a collision. Not all hard braking situations involve longer
distances and more time to react.
The old rusty car. A couple (2!) seconds. I think I'm just going to
let that kind of sit there. I'm starting to see where your education
on the subject comes from.
People can say anything. Megahertz range sounds a bit outside
Wrong, because feeling for the optimum pressure actually doesn't work
as well as you think it does (tests bear this out), and locking up the
brakes is FAR worse yet. In the controlled tests the drivers do not
have to face the panic factor, and STILL they stop shorter with ABS
engaged. This proves without any doubt that at least the test drivers
are not applying as optimal a braking force as the ABS can. And
besides that, in the real world, panic, fear and hormones play a real
part. Real people CAN and DO lock up the brakes on non ABS equipped
vehicles. You think you are beyond that reach. Fine. I won't argue
with you on it. But I KNOW for a fact that skids are COMMON in real
world situations. Go talk to any traffic accident investigator.
You can go on all day about how you think you and most everyone else
can "beat the machine" (which I disagree with) when it comes to
achieving applying just the right amount of brake pressure, but are
you honestly going to try and pretend that even skids are superior to
ABS stops? Or, are you going to pretend that skids are not part of
real world emergency braking. If you neither deny that skids are a
part of real life emergency braking, or that skidding is generally an
inferior way to brake, you must then admit ABS is a benefit if for no
I watch DSC, TLC, SCI, and all that stuff too. I do not deny, nor
have I ever denied that steering control or traction control are
benefits of ABS. What I have said, is that shorter stopping distance
is/was the primary driving force in ABS. More importantly what I have
said, and really the main point I wanted to convey, is that ABS
actually DOES improve stopping distances/times, and that fact is NOT a
myth. It had been stated that ABS results in longer stopping
distance/time. I wanted to rebut that because, it just isn't so.
Here's some reading for you, in case you are interested:
From http://www.culpepperlaw.com/abs.htm :
The History of ABS
When a driver of a vehicle hits conventional brakes hard, the wheels
may lock causing the vehicle to skid, especially on wet and slippery
roads. Antilock brake systems provide the capability for shorter
stopping distances and the ability to steer and to maintain control
during hard braking, especially on wet and slippery surfaces.
Anti-lock braking system
An Anti-lock Braking System (commonly known as ABS) is a system on
motor vehicles which prevents the wheels from locking while braking.
ABS is a very important safety feature, because vehicles become very
unstable when the wheels are locked, braking becomes inefficient and
so braking distances become very long.
From http://www.hwysafety.org/safety_facts/qanda/antilock.htm :
1. How do antilock brakes work? Antilock brakes are designed to help
drivers avoid crashes. When a driver hits regular brakes hard, the
wheels may lock and the vehicle may skid. Wheel lockup can result in
longer stopping distances, loss of steering control and, when road
friction is uneven, loss of stability if the vehicle begins to spin.
The main advantage of antilocks is that they can reduce these problems
on wet and slippery roads. Antilocks work with your car's normal
service brakes to decrease stopping distance and increase the control
and stability of the vehicle during hard braking.
Oh yeah. I forgot to reference this in the other follow-up I just
posted. The following is a link to a study conducted by the US DOT.
They actually employ scientific principles, rather than Eugene (or
other random anecdotal) principles:
It CLEARLY shows that ABS results in better braking distances than the
exact same vehicles with the same drivers do without ABS on. Go read
the report. Read it again if you have to. Then go look at your own
posting (quoted somewhere below convenience) which goes something
"maximizing braking was not a design goal and simply cannot be done
with ABS. The "better braking" is what people are starting to think
and is resulting in more dangerous drivers who will over drive the
Not only can it be done, it IS DONE! And consistently over averages I
Hehe. I also love the part of the posting I read somewhere in this
group (maybe not by you) about salesmen cooking up the false notion of
ABS as a safety feature. Yeah; everyone is all caught up in the
"myth", except for those like you who know what's really going on.
Hehe. What a hoot.
Unless you can site credible articles or sources which actually
scientifically contradict the references I have sited, I suggest you
stifle it, before you really embarrass yourself.
Unless I am mistaken (which is possible) ABS was designed & introduced
for Airplanes in the 1950's. It then slowly migraged into the high
end automobiles and then down to the cheap crap.
The biggest drawback to ABS on car's is that it allows people who
would have previously rear-ended another vehicle with minor
consequences to now steer off the road rolling their cars with major
That being said there are differing calibre's of ABS. For example my
1986 Lincoln Continental had ABS that felt pulsed so fast it felt like
stepping on a vibrator when it was active (as discovered on a night
with freezing rain). I had the misfortune of Driving a Neon & (just
for shit's & giggles) tried out it's ABS. The ABS on the Neon felt
like a mechanical switch being switched on and off. Felt like 2
hertz, probably closer to 20 in reality though. My Old's isn't quite
as fast as my Lincoln but still WAY faster than the Neon.
Question on stopping distance: The Lincoln would stop faster (pound
for pound) than the Neon without a doubt. My personal experiance with
my cars that have had ABS is that, applied correctly (slamming the
brakes on & fully utilizing the ABS) they will usually stop faster
than conventionally equipt cars. However trying to Modulate ABS
yourself will cause a huge extension in stopping distance.
I'm not bad at pedal modulation (my father taught me to drive in a VW
with bald tires in the winter time) but I am no match for ABS. I
have 1 control for 4 wheels. ABS has 1 control per wheel (in the
proper systems). So, if I am trying to prevent 1 wheel from skidding
(threshold braking) I am underbraking 3 others. Good ABS has the
potential to react much much faster on an individual wheel basis than
any human can ever hope to match.
I understand some trucks had an early form of ABS mounted on the
driveshaft that only controlled the rear axle's skidding. The primary
purpose of that (I believe) was to prevent the rear-end from locking
up in unladen conditions.
PS The Lincolns brakes were sweet but the rotor's were $150 each for
the fronts b/c of the ABS adaptors. I somehow doubt that the Neon's
rotors are anywhere near that price, adjusted for inflation. With of
course the corresponding quality of braking.
I never saw it, but I heard some light duty trucks had early rear
"anti-lock" brakes that simply increased rear braking proportionately to
how much weight it was carrying. The more it sagged, the more rear braking.
What this has to do with GM headlights I don't know. ;-)
Correct about 1st used on Airplanes and the time frame. I would add
that it was invented by the German company Bosch. In fact, the "ABS"
letters actually originally were derived from "Antiblockiersystem"
which was the name Bosch had given it.
I don't know if that is the biggest drawback or not, but like anything
in life one thing can lead to another many times.
So true. Some systems are definitely superior to others. For sure 4
wheel ABS with true independent control is the best. My 2001 Camaro
has a very rapid pulse cycle. Without being scientific, I would
estimate perhaps 20 Hertz for the mechanical pulse feel.
Well sure. Once ABS is doing it's job and gripping as tightly as
possible without going into a skid, your brakes themselves are a very
important part of the equation. All discs compared to part drum. Or
Discs with big heavy duty rotors, pads and pistons compared to wimpy
stuff. A heavy car with outstanding brakes often can do better than a
lighter car with poor brakes.
My personal experience is right on par with yours. I learned my
driving on a '69, two wheel drive, "3 on a tree" manual tranny Chevy
pickup in Wisconsin's winter wonderland. I too learned manual brake
modulation, or "pumping" as we used to call it, and totally agree that
a good ABS can beat my ass most any day of the week.
I've read something like that at some point I believe. I don't
remember much about it, but it certainly doesn't seem like one of the
better ABS implementations.
What makes the ABS on my 2000 GM cargo van suck so bad, is the fact that
once the ABS is activated, it continues to pulse for about 1.5 seconds,
even if the tire IS gripping the road. One and a half seconds of ABS
braking is simply FAR TOO LONG! Now add in the situation where the ABS
is activating over and over for 3 or 4 cycles. Now we have 4.5 to 6
seconds of partial braking! This lag time of having partial braking for
so long results in longer stopping distances. I suppose if the ABS
didn't disable the brakes as much as it does, and if it were much faster
reacting, or *deactivating* itself when not needed, then it might
actually do what it is intended to do. But as it is, it sucks, and it
increases stopping distances in most situations in my real life driving
It wasn't on gods green earth, it was on mans bumpy highway at 70 or so
mph and an accident in front of me. Luckily, (yes luckily!) I was
pulling a trailer and used those brakes manually. Yes, the trailer with
a couple tons in it slowed me down better than the ABS crap. And yes,
using them manually, with all four wheels on the trailer locked up most
of the time. If you have ever pulled a trailer with brakes, you get a
feeling for it and can easily feel if the trailer is pushing you ahead
or holding you back. It held me back.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.