Real World Antilock Brakes

[siyan]

So a while ago we were getting fresh, fluffy snow, and I?m driving about 30 km/h keeping pace with everyone else. Red light comes up, everyone hits the brakes. They all stop just fine, whereas my ABS decides that it?s a good idea to continually let up on the brakes, forcing me to yank on the E-brake to stop in time. This is with just fresh snow on top of dry pavement, at 30km/h.

This also happened as I was about to pull out of my apartment's parking lot, though it was packed snow on top of rough ice with some rocks in it. On the other hand I was doing a scant 10-15 km/h. Once again had to pull the ebrake to avoid getting hit by traffic.

Does my car suck?

 

[James Bond]

All signs point to yes.

 

[SVT Cobra]

Could it be you're an idiot for not knowing your cars breaking capabilities and not keeping the proper distance?

 

[slikmunks]

in theory, if your anti-lock brakes are coming on and you pull the e-brake, you're not helping, you're making it worse b/c now your rear wheels are locked up are providing less than full stopping power under those conditions...

ASSUMING your anti-lock brakes are working correctly...

ABS should be just past threshold braking, and any harder you'll skid and you'll slow down more slowly... which is why the ABS comes on, to keep you from just sliding forward.

so either it's in your head, or your abs isn't working... i'd get both checked out

 

[Zenmervolt]

ABS causes longer stopping distances on slick surfaces than completely locked brakes. It always will. What it provides, however, is increased car control during the stop. You should NEVER rely on ABS, and if you're braking hard enough on snow to trigger it (outside of emergency, panic-stop, situations), you're doing something wrong.

Your car does not suck. Your driving skills do.

ZV

 

[giantpinkbunnyhead]

LOL maybe your ABS is wonky? altough, in deep snow, some claim that ABS hurts more than it helps. While a skidding tire generally has less stopping force than a rotating one, what happens in the snow is that a skidding tire is more likely to build up a wall of snow in front of it, which can help further slow the vehicle. I drive in the snow six months a year and can't say I've noticed if this is true or not, but it's all I can come up with. Just curious.. what kind of car?

 

[Philippine Mango]

Sounds like the ABS is working, though I don't know what it's really like since I'm not there and I'm sure it's difficult to describe whats going on. ABS works by not locking the wheel so it's suppose to letup on the wheels to prevent locking. Though locking is actually better in snow because all the snow you'll build up infront of the tires, creating friction etc.

 

[slikmunks]

Originally posted by: Zenmervolt
ABS causes longer stopping distances on slick surfaces than completely locked brakes. It always will. What it provides, however, is increased car control during the stop. You should NEVER rely on ABS, and if you're braking hard enough on snow to trigger it (outside of emergency, panic-stop, situations), you're doing something wrong.

Your car does not suck. Your driving skills do.

ZV

i've never heard this...

not calling bs on you, just never heard it... anywhere...

physics doesn't support this either, as the static coefficient of friction is higher than the kinetic coefficient of friction... and if the wheel is skidding, you're working with kinetic friction...

and if it were a wall of snow building up, it'd have to be a HUGE wall i would think... and i would also think that stopping on a layer of snow (rotating wheel) would be better than skidding on the ice (below the layer of snow) to build up a wall of snow that will slow down a xxxx lb car...

 

[SampSon]

I'm not a huge fan of ABS in the snow.

 

[Zenmervolt]

Originally posted by: slikmunks
ABS should be just past threshold braking, and any harder you'll skid and you'll slow down more slowly... which is why the ABS comes on, to keep you from just sliding forward.

Yes and no. Tests have shown that on anything other than either dry or merely wet pavement (e.g. sand, gravel, snow, ice, etc), locked wheels will show the car down faster than ABS will. However, locked wheels give zero control, and it's better to have control.

The reason that ABS does not work well with gravel/sand/snow/ice is because the coefficient of friction is so small that the wheels don't pick up speed fast enough once the ABS lets off the calipers and therefore it cannot pulse optimally.

I'd still rather have control in the emergency situation though, so I think the tradeoff is a good one.

ZV

 

[Pepsi90919]

what municipality do you live in?

 

[Zenmervolt]

Originally posted by: slikmunks

Originally posted by: Zenmervolt
ABS causes longer stopping distances on slick surfaces than completely locked brakes. It always will. What it provides, however, is increased car control during the stop. You should NEVER rely on ABS, and if you're braking hard enough on snow to trigger it (outside of emergency, panic-stop, situations), you're doing something wrong.

Your car does not suck. Your driving skills do.

ZV

i've never heard this...

not calling bs on you, just never heard it... anywhere...

physics doesn't support this either, as the static coefficient of friction is higher than the kinetic coefficient of friction... and if the wheel is skidding, you're working with kinetic friction...

and if it were a wall of snow building up, it'd have to be a HUGE wall i would think... and i would also think that stopping on a layer of snow (rotating wheel) would be better than skidding on the ice (below the layer of snow) to build up a wall of snow that will slow down a xxxx lb car...

See my other post. It has to do with the ability of the ABS system to re-apply braking force to the wheels.

Road and Track did some testing a couple years back, I don't remember the issue off the top of my head, and I think it's too old to be online, but I will check later tonight.

EDIT: Road & Track, July 1997, pp 99-105. Can post full text if you wish.

ZV

 

[smitbret]

Wrong, in almost all cases it will shorten stopping distances because a locked up wheel provides less stopping force than a wheel that is having it's brakes pumped. It's like when you are sliding across a freshly waxed floor or walking/jogging across a freshly waxed floor in stocking feet. You can stop more quickly when your feet are moving than if they have already broken traction on the floor.
-Brett

 

[slikmunks]

Originally posted by: Zenmervolt

Originally posted by: slikmunks
ABS should be just past threshold braking, and any harder you'll skid and you'll slow down more slowly... which is why the ABS comes on, to keep you from just sliding forward.

Yes and no. Tests have shown that on anything other than either dry or merely wet pavement (e.g. sand, gravel, snow, ice, etc), locked wheels will show the car down faster than ABS will. However, locked wheels give zero control, and it's better to have control.

The reason that ABS does not work well with gravel/sand/snow/ice is because the coefficient of friction is so small that the wheels don't pick up speed fast enough once the ABS lets off the calipers and therefore it cannot pulse optimally.

I'd still rather have control in the emergency situation though, so I think the tradeoff is a good one.

ZV

good to know, and yes, i concur, i'd rather have control...

so... what kind of car is this?

 

[SparkyJJO]

How old is the car? My parents' old ford windstar (piece of junk, kept breaking stuff) had an issue with the ABS and they would get set off for no particular reason. Apparently there was a bad sensor, replacing that fixed it.

 

[Zenmervolt]

Originally posted by: slikmunks

Originally posted by: Zenmervolt

Originally posted by: slikmunks
ABS should be just past threshold braking, and any harder you'll skid and you'll slow down more slowly... which is why the ABS comes on, to keep you from just sliding forward.

Yes and no. Tests have shown that on anything other than either dry or merely wet pavement (e.g. sand, gravel, snow, ice, etc), locked wheels will show the car down faster than ABS will. However, locked wheels give zero control, and it's better to have control.

The reason that ABS does not work well with gravel/sand/snow/ice is because the coefficient of friction is so small that the wheels don't pick up speed fast enough once the ABS lets off the calipers and therefore it cannot pulse optimally.

I'd still rather have control in the emergency situation though, so I think the tradeoff is a good one.

ZV

good to know, and yes, i concur, i'd rather have control...

so... what kind of car is this?

The car used in the R&T test was a '97 Mercedes S600.

ZV

 

[siyan]

I'm fully aware of how ABS works, I'm merely wondering if ABS makes pure-straight line stopping distance worse in some cases. And it would seem like yes.

I'm also quite a good driver. I don't think that keeping the same following distance as everyone else and going the same speed, but being forced by my car to pull the ebrake makes me a poor driver. The other option, of course, was to bump into the guy at about 5km/h.

Originally posted by: slikmunks
and if it were a wall of snow building up, it'd have to be a HUGE wall i would think... and i would also think that stopping on a layer of snow (rotating wheel) would be better than skidding on the ice (below the layer of snow) to build up a wall of snow that will slow down a xxxx lb car...

wasn't any ice. snow on dry pavement.

 

[Jahee]

Originally posted by: Zenmervolt

Originally posted by: slikmunks

Originally posted by: Zenmervolt
ABS causes longer stopping distances on slick surfaces than completely locked brakes. It always will. What it provides, however, is increased car control during the stop. You should NEVER rely on ABS, and if you're braking hard enough on snow to trigger it (outside of emergency, panic-stop, situations), you're doing something wrong.

Your car does not suck. Your driving skills do.

ZV

i've never heard this...

not calling bs on you, just never heard it... anywhere...

physics doesn't support this either, as the static coefficient of friction is higher than the kinetic coefficient of friction... and if the wheel is skidding, you're working with kinetic friction...

and if it were a wall of snow building up, it'd have to be a HUGE wall i would think... and i would also think that stopping on a layer of snow (rotating wheel) would be better than skidding on the ice (below the layer of snow) to build up a wall of snow that will slow down a xxxx lb car...

See my other post. It has to do with the ability of the ABS system to re-apply braking force to the wheels.

Road and Track did some testing a couple years back, I don't remember the issue off the top of my head, and I think it's too old to be online, but I will check later tonight.

EDIT: Road & Track, July 1997, pp 99-105. Can post full text if you wish.

ZV

Would you please?..

 

[BD2003]

Originally posted by: siyan
I'm fully aware of how ABS works, I'm merely wondering if ABS makes pure-straight line stopping distance worse in some cases. And it would seem like yes.

The answer is indeed yes. But as others have said, ABS is about decreasing stopping distance as it is about maintaining control during hard braking.

I'd much rather have the opportunity to steer out of the way of an obstacle than plow into someones rear end at a lower speed. If you're skidding, forget about steeering.

ABS has saved my ass on slick and dry roads. Someone braked hard in front of me in the rain because they decided that they wouldnt make the yellow light, and if I didnt have ABS and was able to steer out of the way, I would most definitely have hit him.

With an older car without ABS, I was in the exact same situation, slammed on the brakes, and I just ended up skidding to within an inch of him, steering to the side was completely ignored by the locked up tires.

ABS FTW...I'll never drive a car without them.

I'm also quite a good driver. I don't think that keeping the same following distance as everyone else and going the same speed, but being forced by my car to pull the ebrake makes me a poor driver. The other option, of course, was to bump into the guy at about 5km/h

Yeah, it kinda does make you a bad driver actually. In normal traffic, if you have to pull your ebrake, ABS or not, you're too damn close or braking too late.

Or you really need to get your pads and tires checked, pronto.

wasn't any ice. snow on dry pavement.

Snow might as well be ice if your tires aren't built for it.

 

[Howard]

Originally posted by: Zenmervolt
ABS causes longer stopping distances on slick surfaces than completely locked brakes.

Stopping distances decreased substantially with four-wheel ABS on wet surfaces, but decreased only slightly on dry pavement and increased considerably on gravel.

http://www.nhtsa.dot.gov/cars/rules/regrev/evaluate/808206.html

 

[IHateMyJob2004]

Originally posted by: Howard

Originally posted by: Zenmervolt
ABS causes longer stopping distances on slick surfaces than completely locked brakes.

Stopping distances decreased substantially with four-wheel ABS on wet surfaces, but decreased only slightly on dry pavement and increased considerably on gravel.

http://www.nhtsa.dot.gov/cars/rules/regrev/evaluate/808206.html

Interesting.


Bottom line ... it's winter and you can't drive like an idiot. Start braking early, etc ...

 

[AgentJean]

Well since your brakes are not working, I hope your inertia dampers and structural integrity field is in proper working order.





You're going to need it.

 

[DaWhim]

Originally posted by: Howard

Originally posted by: Zenmervolt
ABS causes longer stopping distances on slick surfaces than completely locked brakes.

Stopping distances decreased substantially with four-wheel ABS on wet surfaces, but decreased only slightly on dry pavement and increased considerably on gravel.

http://www.nhtsa.dot.gov/cars/rules/regrev/evaluate/808206.html

not for my car. when my abs kicks in, I can feel like I lose my brake.

 

[Strk]

Originally posted by: siyan
I'm fully aware of how ABS works, I'm merely wondering if ABS makes pure-straight line stopping distance worse in some cases. And it would seem like yes.

I'm also quite a good driver. I don't think that keeping the same following distance as everyone else and going the same speed, but being forced by my car to pull the ebrake makes me a poor driver. The other option, of course, was to bump into the guy at about 5km/h.

Originally posted by: slikmunks
and if it were a wall of snow building up, it'd have to be a HUGE wall i would think... and i would also think that stopping on a layer of snow (rotating wheel) would be better than skidding on the ice (below the layer of snow) to build up a wall of snow that will slow down a xxxx lb car...

wasn't any ice. snow on dry pavement.

My brother thinks he is quite a good driver too, but in his eleven years of driving, he has never gone a year without an accident, even when he didn't have a car for most of a year. Hell, he's caused three in just the driveway that I know of.

 

[sixone]

Originally posted by: siyan
I'm also quite a good driver. I don't think that keeping the same following distance as everyone else and going the same speed, but being forced by my car to pull the ebrake makes me a poor driver. The other option, of course, was to bump into the guy at about 5km/h.

When you're driving the same kind of car as everyone else, then this would be a good rule to stick to. Otherwise, you need to know YOUR car's capabilities, and adjust YOUR driving accordingly. That's what a good driver does.