Interesting observation about ABS and 02 WRX

[Mark]

I have a questions about something I noticed yesterday when I was
driving my 02 WRX and it's ABS system.

First of all here in KY we have had some interesting winter weather
the past week. Seems we have been getting a lot of ice this winter.
Anyway, I was driving around town yesterday and I needed to make a
left hand turn. The turn lane I was in still had some snow/ice from a
winter storm we had a few days ago. In my lane, the left tires were
on strip of solid ice/snow however the right side tires were on
totally dry pavement. When I pressed the brakes, I felt the left tired
pulsate due to the antilock brakes being activated however I was not
slowing down (the left tires were still turning). Since no one was
around me, and I still had plenty of time to turn, I wanted to see
what would happen if I pressed the brakes harder. Well, the car kept
on going and would not slow down. I also tried to pump the brakes and
still I kept moving forward at the same speed. I expected to at least
be slowing down a little from the brakes on the right side.

I started thinking about this and I would have assumed that at least
the right side brakes would help slow down the car since it's tires
were on dry pavement. It seemed that since the left brakes didn't
have any traction, the ABS also assumed the right side did have
traction.

Besides this *quirk* from this one occasion, my brakes have behaved
normally. My question to this NG is, does the sensor for wheel "A"
have any control over what the other 3 wheel are doing?

 

[David]

I started thinking about this and I would have assumed that at least
the right side brakes would help slow down the car since it's tires
were on dry pavement.

I thought that was the main point of ABS brakes: controlled stops in circumstances
like that. On dry or wet pavement, if anything I think it extends stopping distances,
but I thought they would shorten in mixed conditions like what you describe.

 

[Jim Stewart]

I have a questions about something I noticed yesterday when I was
driving my 02 WRX and it's ABS system.

First of all here in KY we have had some interesting winter weather
the past week. Seems we have been getting a lot of ice this winter.
Anyway, I was driving around town yesterday and I needed to make a
left hand turn. The turn lane I was in still had some snow/ice from a
winter storm we had a few days ago. In my lane, the left tires were
on strip of solid ice/snow however the right side tires were on
totally dry pavement. When I pressed the brakes, I felt the left tired
pulsate due to the antilock brakes being activated however I was not
slowing down (the left tires were still turning). Since no one was
around me, and I still had plenty of time to turn, I wanted to see
what would happen if I pressed the brakes harder. Well, the car kept
on going and would not slow down. I also tried to pump the brakes and
still I kept moving forward at the same speed. I expected to at least
be slowing down a little from the brakes on the right side.

The car did the proper thing.

Without antilock brakes, the result of what you
did could have been a vicious spin to the right.

If the car spins, all bets are off. If it goes
straight and hits something, at least the airbags
and crumple zones will save your ass.

 

[T]

I thought that was the main point of ABS brakes: controlled stops in circumstances
like that. On dry or wet pavement, if anything I think it extends stopping distances,
but I thought they would shorten in mixed conditions like what you describe.

The main point is to retain control instead of spinning around.

This will most of the time increase stopping distances. ABS drivers need
to learn "Steer your way out of it" on an unconscious level.

TBerk

 

[David Betts]

I thought that was the main point of ABS brakes: controlled stops in circumstances
like that. On dry or wet pavement, if anything I think it extends stopping distances,
but I thought they would shorten in mixed conditions like what you describe.

Completely the opposite. ABS prevent detects incipient wheel lock-up
and prevents it. This is to allow you to retain steering control. In
slippery conditions it will, therefore, increase stopping distances.
(Of course, in extreme slippery conditions you should hardly be using
the brakes atall anyway <g>.)

David Betts
(e-mail address removed)

 

[2 Stroke]

You describe a problem that many of us have experienced. The WRX has
a bug in its ABS logic that causes what you describe. Subaru is in
denial, probably because of the potential cost of a recall on all MY02
& MY03 WRX's. The problem has been resolved in the MY04.

Here's one of many links that document the problem:

http://forums.nasioc.com/forums/showthread.php?s=&threadid=487735

Regards,
Steve Hansen

=============================================================

 

[BoB]

I have a questions about something I noticed yesterday when I was
driving my 02 WRX and it's ABS system. SNIP
Besides this *quirk* from this one occasion, my brakes have behaved
normally. My question to this NG is, does the sensor for wheel "A"
have any control over what the other 3 wheel are doing?

Yes, when skidding is detected by the sensor, it transfers braking to
other wheels. When all wheels detect skidding you are SOL when it comes
to stopping.

My wife, traveling at 15 mph in our '95 Legacy wagon, began descent on
a curved slight grade. After committing to the 100 yard stretch of
heavily traveled roadway, she could see cars piled up, completely
blocking the street near the bottom. With steep ditches on both sides,
she assumed that she would be able to stop in time as the vehicles were
still 50 yds away. Nope, she rode the brake all the way and piled into
the others still traveling about 5 mph. If the brakes had locked-up all
wheels, she could surely have stopped in that distance. Maybe in the
ditch but probably no more expensive than the $4,000 she incurred. I
really wish she had avoided the rear of the old jeep with the high
mounted trailer hitch though.

That was the only time ABS came into play in 10 years and we are NOT
real thrilled with them under 'those' conditions. SUVs with trailer
hitches mounted higher than the average bumper height should have their
insurance premiums automatically doubled. $4,000 damage at 5 mph, jeez.

BoB

 

[Tony Hwang]

Yes, when skidding is detected by the sensor, it transfers braking to
other wheels. When all wheels detect skidding you are SOL when it comes
to stopping.

My wife, traveling at 15 mph in our '95 Legacy wagon, began descent on
a curved slight grade. After committing to the 100 yard stretch of
heavily traveled roadway, she could see cars piled up, completely
blocking the street near the bottom. With steep ditches on both sides,
she assumed that she would be able to stop in time as the vehicles were
still 50 yds away. Nope, she rode the brake all the way and piled into
the others still traveling about 5 mph. If the brakes had locked-up all
wheels, she could surely have stopped in that distance. Maybe in the
ditch but probably no more expensive than the $4,000 she incurred. I
really wish she had avoided the rear of the old jeep with the high
mounted trailer hitch though.

That was the only time ABS came into play in 10 years and we are NOT
real thrilled with them under 'those' conditions. SUVs with trailer
hitches mounted higher than the average bumper height should have their
insurance premiums automatically doubled. $4,000 damage at 5 mph, jeez.

BoB

Hi,
She could pull the parking brake handle.
ABS has it's short comings for sure. Pro drivers can do better
with regular brakes.
Tony

 

[David Betts]

ABS has it's short comings for sure. Pro drivers can do better
with regular brakes.

Not when it comes to avoiding accidents, no. It is not physically
possible to cadence brake at the rate of abs. The whole point of abs
is to allow you to steer round an obstruction whilst carrying out an
emergency stop. 'Pro' drivers, of course, use abs for quite a
different purpose - to allow them to brake to the maximum right to the
apex whilst turning into a corner without wheel locking. (It is banned
in most forms of circuit racing as a 'driver-aid'.)

There will, of course, be circumstances when you can stop quicker by
locking the wheels to create a 'plough' effect in gravel or some types
of snow. On ice or other very slippery surfaces, however, you're
likely to slide just as far - or further - with the wheels
locked.....plus you will be out of control.

At the end of the day, of course, if you activate the abs in normal
road driving then you are braking too hard for the conditions anyway.
Had the fun of glazed sheet ice on all the local side roads last week.
Managed to stop for all the road junctions - including the downhill
ones - without activating the abs once. It's simply a matter of
planning further ahead and only caressing the brakes to take off that
last two or three mph.

(As for our initial correspondent's suggestion that the brakes should
work on one side and not the other when only one side is
slippery...... how does a tank steer? <g>)

David Betts
(e-mail address removed)

 

[BoB]

BoB wrote: [My whining snipped]
Hi,
She could pull the parking brake handle.
ABS has it's short comings for sure. Pro drivers can do better
with regular brakes.
Tony

She was so advised, but after-the-fact.

Her daughter-in-law had just slid into another Jeep when turning the
last corner before they arrived at her home, so my wife was being as
careful as possible. They had been downtown, inside the convention
center, and was totally surprised to see 2"+ of un-predicted snow when
they emerged to head home.

Several years ago, as she left for town, she did a 180 at the first
intersection and returned home. We returned to the corner so I could
show her how she 'should have handled it'. After doing the same damn
thing, I got quite a ribbing as we returned home. It turned out to
be deep ruts in the ice beneath the snow that was a real surprise
when car pretty much followed the ruts regardless of attempt to steer.

Therefore, on her most recent encounter, I wasn't to critical about
how 'I would have handled it'.

BoB

 

[Mark]

You describe a problem that many of us have experienced. The WRX has
a bug in its ABS logic that causes what you describe. Subaru is in
denial, probably because of the potential cost of a recall on all MY02
& MY03 WRX's. The problem has been resolved in the MY04.

Here's one of many links that document the problem:

http://forums.nasioc.com/forums/showthread.php?s=&threadid=487735

Regards,
Steve Hansen

Thanks for all the replies.

However, I have to say that I also think this is NOT normal behavior.
Remember, In my circumstance the right side wheels were on totally dry
payement and could have provide some braking assistance. I don't see
how the car would have gone out of control while the right side wheels
were still providing normal traction. Now, IF I said that the right
side wheels were also detecting slipage, then I would agree that no
traction should equal no braking and the car would have kept going at
the same speed.

Can't wait for the next snow fall, I want to go out and try this
experiment again in a safe parking lot. If anyone else get a chance to
try it, please post your results to this NG for others.

Thanks again for everyones opinion.

 

[David Buchner]

ABS drivers need to learn "Steer your way out of it" on an unconscious
level.

This may be useful in traffic. But not so useful on narrow dirt roads
with trees on both sides, when a herd of deer leaps in front of me.

I agree that it's a factor that experienced drivers must adapt to, and
develop new skills to work around -- but I don't agree that it's an
improvement.

 

[Tony Hwang]

BoB wrote:

[My whining snipped]

Hi,
She could pull the parking brake handle.
ABS has it's short comings for sure. Pro drivers can do better
with regular brakes.
Tony

She was so advised, but after-the-fact.

Her daughter-in-law had just slid into another Jeep when turning the
last corner before they arrived at her home, so my wife was being as
careful as possible. They had been downtown, inside the convention
center, and was totally surprised to see 2"+ of un-predicted snow when
they emerged to head home.

Several years ago, as she left for town, she did a 180 at the first
intersection and returned home. We returned to the corner so I could
show her how she 'should have handled it'. After doing the same damn
thing, I got quite a ribbing as we returned home. It turned out to
be deep ruts in the ice beneath the snow that was a real surprise
when car pretty much followed the ruts regardless of attempt to steer.

Therefore, on her most recent encounter, I wasn't to critical about
how 'I would have handled it'.

BoB

Hi,
BTW, do you have set of good winter tires on the car? My boy drives
souped up Impreza RS, manual shift. I put on a set of Michelin Arctic
Alpin for the season. He drives like ding bat but so far never lost
control. If you pull ABS fuse, it'll be regular brake(?)
My daughter drives same car with automatic shift with same winter tires.
Goes skiing almost every week t the mountain, no problem so far.
Tony

 

[S]

Hi Mark, All!

I have a questions about something I noticed yesterday when I was
driving my 02 WRX and it's ABS system.

This is frequently a fairly hotly debated topic, both here and
elsewhere on the Web. Those of us who aren't happy with the ABS
performance on "non-standard" surfaces have found it beneficial to
install a switch on the dash to disable the ABS function as needed.
This takes about 1/2 hour to accomplish, and results in your ABS
warning light illuminating when disabled, so you aren't likely to
forget to turn 'em back on when you return to nice dry pavement.
Instructions to perform this mod are available in various places on
the Web, or feel free to contact me directly for the nfo.

ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[Guest]

This is frequently a fairly hotly debated topic, both here and
elsewhere on the Web. Those of us who aren't happy with the ABS
performance on "non-standard" surfaces have found it beneficial to
install a switch on the dash to disable the ABS function as needed

My '89 GT wagon hasn't got ABS but I've been test driving a new
Corolla out of curiosity to experience ABS before I get a new TS or
WRX.

We drive on steep town hills and mountain roads on snow and ice about
four months of the year here, and I've done some rally driving way
back so I'm not a novice.

I love ABS - at least on the Corolla!

So far, when I have tested it on slick deserted roads or an empty
parking lot I have found it gives me far more control than standard
brakes, plus I have not detected any unexpected increase in stopping
distance.

One of the best things about ABS is that one can test road traction at
speed at any time safely by giving a quick jab at the brake to
determine slipping point. With ABS that a far safer procedure than
without.

Of course, if the surface is totally slick glare ice with no traction
at all, then nothing would help except good ice studs.

So...is the Subaru ABS system somehow different or worse than Toyota?

 

[Ken Gilbert]

might want to check this thread out:

http://forums.nasioc.com/forums/showthread.php?threadid=487735

hth
ken

 

[Verbs Under My Gel]

Thanks for all the replies.

However, I have to say that I also think this is NOT normal behavior.
Remember, In my circumstance the right side wheels were on totally dry
payement and could have provide some braking assistance. I don't see
how the car would have gone out of control while the right side wheels
were still providing normal traction. Now, IF I said that the right
side wheels were also detecting slipage, then I would agree that no
traction should equal no braking and the car would have kept going at
the same speed.

Can't wait for the next snow fall, I want to go out and try this
experiment again in a safe parking lot. If anyone else get a chance to
try it, please post your results to this NG for others.

Thanks again for everyones opinion.

It _is_ normal behaviour. You've no friction force acting on the left
hand side of the car (it's on snow/ice). If the brakes on the right
side were to be applied (such as would happen in a non-ABS equipped
car), guess what would happen? The entire car would rotate clockwise
(as viewed from above) about its center of mass. You'd now be getting
T-boned by traffic approaching in the lane to your right.

Bottom line, you need to expect this behavior in an ABS-equipped car,
and modify your driving style accordingly.

 

[CompUser]

It _is_ normal behaviour. You've no friction force acting on the left
hand side of the car (it's on snow/ice). If the brakes on the right
side were to be applied (such as would happen in a non-ABS equipped
car), guess what would happen? The entire car would rotate clockwise
(as viewed from above) about its center of mass. You'd now be getting
T-boned by traffic approaching in the lane to your right.

Agree with verbs. Someone else mentioned "how a
tank steers" and that is how the original poster
proposes ABS should work. If it did work that
way, the result would have been like a tank
steering...stop the right track, let left track
continue rotating, ta-da! We have "pivot steer",
where the tank turns on dime.

Actually, verb, the car would rotate somewhere
between it's center of mass and point(s) of
greatest friction--the two right wheels with dry-
lane traction. Either way, bad business.

Steve

 

[R]

CompUser wrote:

Actually, verb, the car would rotate somewhere
between it's center of mass and point(s) of
greatest friction--the two right wheels with dry-
lane traction. Either way, bad business.

Steve

I noticed this in my car, too. When one side is on ice,
the ABS tends to lift the brakes on all four wheels.
This almost sent me rolling into an intersection once.
Is it really supposed to do this?

 

[Jim Stewart]

It _is_ normal behaviour. You've no friction force acting on the left
hand side of the car (it's on snow/ice). If the brakes on the right
side were to be applied (such as would happen in a non-ABS equipped
car), guess what would happen? The entire car would rotate clockwise
(as viewed from above) about its center of mass. You'd now be getting
T-boned by traffic approaching in the lane to your right.

I saw this demonstrated on a skid pad. One side
was dry, the other hosed down with running water.
With ABS, the car stopped straight ahead. Without,
the car made a *vicious* spin. Made me a believer.