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Old 01-02-2013, 01:45 AM   #1
bobdole888
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Default ABS didn't engage on icy road, VDC problem?

I was driving on icy road, going about 20 mph. Slowed down to about 5 mph with brakes applied, and then the car either started skidding or lost brake power. For about 15ft, my impreza just went straight, but didn't decelerate with brake fully applied. It only stopped when I rear ended another car. The ABS never engaged, no pulsating brakes, or ABS light coming on.

Later that day, I tried braking at 5mph in a snowy parking lot and ABS came out every time. I couldn't understand why ABS didn't come on before I crashed into someone.

I saw some posting about Subaru Legacy losing brake power when one side of wheels are on icy surface while the other side is on surface with traction. I'm wondering if that's what happen to me.

Could VDC have caused braking power to be lost? To prevent a spin out, did VDC prevents ABS and brakes from being applied to keep the car going straight? I didn't see VDC light coming on either.

Or did Subaru "enhanced" the ABS to lock up wheels on icy surface and not have the brakes pulsate?
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Old 01-02-2013, 08:15 AM   #2
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Could there been some fault on your end?
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Old 01-02-2013, 09:18 AM   #3
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Usually ABS only activates when a sudden brake force is applied. If you were already on the the brakes and increased pedal pressure, the ABS would not have activated. When you were trying to test it later, were you just stomping the pedal, or steadily increasing brake pressure? If my theory is correct, if you had released the pedal then re-applied the brakes, the ABS might have activated.

Either way..it really sucks that you got into an accident.
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Old 01-02-2013, 09:33 AM   #4
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Ice without studded tires or very good snow tires that can provide traction will not allow any traction at all, so ABS would not have helped because the tires would still have been lacking traction.

I read a while back that in Germany, when ABS first was introduced, insurance companies started giving discounts to drivers who had it, but later retracted the discount because many drivers with ABS were not using common sense and were driving too fast with too little distance between them an other drivers to reduce their risk of accidents -- I think the number of fender benders increased so they pulled the discount.

What tires do you have on your car?
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Old 01-02-2013, 11:06 AM   #5
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ice is ice, no way abs is gonna help you there. There is no traction to be had, maybe your wheel didn't lock up and was just sliding.
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Old 01-02-2013, 11:51 AM   #6
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Quote:
Originally Posted by Ladeef View Post
maybe your wheel didn't lock up and was just sliding.
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Old 01-02-2013, 12:14 PM   #7
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I am running on stock Yoko tires, so I agree that they won't provide optimal traction on ice. After some reading, I found that stopping distance on ice can be 10x of dry pavement so I do realize it's hard to stop on ice.
My interest is know what is the expected behavior of the ABS/VDC on the '12 impreza. I know that ABS probably would not have helped in my situation. I allowed for 2x stopping distance, but didn't allow for 10x.
I would have expected that ABS to kick in the moment my car started sliding.
Since that didn't happen, I thought maybe the VDC over-rided the ABS to prevent possible spin out.
Or could it be that my brake disc had a layer of ice on it and the pad/disc itself was sliding not the tire? I had only driven the car for about 1min at this point, and this was the first time I was applying brake outside of parking lot.
Essentially, I got out of the the parking lot and the 1st red light that was just 1 block away is when my impreza failed to stop. I did slow down from 20mph to about 5mph.
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Old 01-02-2013, 12:27 PM   #8
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If all the tires are locked up, will the car think it is stopped if youre sliding?

This is a bad thread in a good way. Bad because its unfortunate, but good to teach others.
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Old 01-02-2013, 12:52 PM   #9
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Quote:
Originally Posted by myrt1987 View Post
If all the tires are locked up, will the car think it is stopped if youre sliding?

This is a bad thread in a good way. Bad because its unfortunate, but good to teach others.
That's an interesting thought. I don't know how the car would know it's still moving when all wheels are locked... I don't have GPS. Car did slow down sufficiently to 5mph so if the wheels locked maybe it just thought the car stopped. I think motion sensors only sense acceleration/deceleration, not constant speed.

Anyway, I still have no conclusion if my tires were sliding or if my brakes were sliding.

The day after the accident, I tried stomping on the brake as I was coming out of the parking lot and found that my impreza slid the first 2 times with no ABS, and the follow 3 times ABS engaged. All 5 test, I was going about 5mph.
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Old 01-02-2013, 12:55 PM   #10
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Quote:
Originally Posted by myrt1987 View Post
If all the tires are locked up, will the car think it is stopped if youre sliding?
i don't think so, no other car i have had has behaved like that.

i slid on the ice about 5 weeks ago, almost into a curb after VDC descided to stop my fun. all i could do was ride it out because i put the brakes on, the brakes were pulsing, and I couldn't do anything on the glare ice.

i am going to test the press the brake, then press harder theory tonight to see if i can get the ABS to kick in.
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Old 01-02-2013, 01:13 PM   #11
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BobDole, where do you live? Is it an area of the country where winter temps are regularly below 40*? Many people who are snow tire advocates (I'm one of the them) will tell you that snow tires are helpful in the cold, not just the snow, because they're made from rubber compounds that stay soft in the cold. Most all-season tires get hard below 40*, thus losing their effectiveness even when the roads are dry.

I know this has nothing to do with your black ice scenario. I'm just pointing out that you might want to consider a set of snow tires, if where you live justifies it. This accident was at 5 mph. The next time might be faster.
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Old 01-02-2013, 01:22 PM   #12
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Quote:
Originally Posted by flyboy1100 View Post
i don't think so, no other car i have had has behaved like that.

i slid on the ice about 5 weeks ago, almost into a curb after VDC descided to stop my fun. all i could do was ride it out because i put the brakes on, the brakes were pulsing, and I couldn't do anything on the glare ice.

i am going to test the press the brake, then press harder theory tonight to see if i can get the ABS to kick in.
Thanks! That info would be helpful.
I have braked on wet road before where I slow down from 35 to about 5mph, then braked harder and observed ABS kick in on the final stretch. I wouldn't have thought you have to have a 'fresh' stomp on the brake to get ABS activated.

I was on a ski trip when the accident happened, where I live I don't get snow, so I can't do any more testing, now that I'm back home. I only ski about 2 times a year, so I can't justify getting snow tires just for the 2 trips per year.
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Old 01-02-2013, 01:26 PM   #13
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Quote:
Originally Posted by bobdole888 View Post
That's an interesting thought. I don't know how the car would know it's still moving when all wheels are locked... I don't have GPS.
That's pretty much it right there.

The following is an oversimplified explanation but here goes: ABS works by calculating the wheel rotation between all 4 wheels. If during braking, some of the wheels stop while others are still turning, the computer realizes that those wheels have locked up and it engages the ABS on the wheels that have stopped.

However, if all 4 wheels stop rotating at the same time, (for example, what could happen when braking on ice at low speed) then the ABS system assumes the car stopped and thus, doesn't engage the ABS.

In any case, sorry you got in a fender bender. I had almost the same thing happen to me a few years ago in my FJ Cruiser. Really bad tires + ice = a bad time.
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Old 01-02-2013, 01:51 PM   #14
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Sorry you got into an accident. Had a similar situation happen to me last week but it was clearly my own stupidity that was the cause. I still have the stock Yokos and came hauling butt into the parking lot at work after a snowfall and went sliding towards the bosses car! Thankfully I was able to steer clear and keep on going without hitting anything. I too had the impression that the brakes were sliding/ABS not engaged but my VDC light did come on. Ordering my snow tires shortly! :-)
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Old 01-02-2013, 03:16 PM   #15
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Snow tires cheaper than your deductible or body repair or lost of life 450 for four altimax arctic and that's not even the on sale price
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Old 01-02-2013, 03:22 PM   #16
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I concur with PuyallupCoug said. ABS works by calculating the difference between wheel speeds. If there's no difference, it will not engage. This happened to my friends this past two weeks(AS tires in WV snowy mountain roads in late-model Mazda and Toyota).

Fundamental braking technique is if all wheels are locked up, is to let off the brakes and get back on it smoothly.
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Old 01-02-2013, 03:57 PM   #17
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Quote:
Originally Posted by K2e2vin View Post
I concur with PuyallupCoug said. ABS works by calculating the difference between wheel speeds. If there's no difference, it will not engage. This happened to my friends this past two weeks(AS tires in WV snowy mountain roads in late-model Mazda and Toyota).

Fundamental braking technique is if all wheels are locked up, is to let off the brakes and get back on it smoothly.
I don't think ABS compares the difference between different wheels speeds, though VDC does work out how all 4 wheels are moving or not to maintain stability and works with the symmetrical AWD and ABS to regulate the wheel spin.

ABS uses individual sensors on each wheel to regulate the brake pressure for that wheel. But in our cars you cannot separate ABS and VDC.

In general if you are out driving in snow or ice don't try to modulate the brakes yourself, use the push and hold technique and let the car work it out. If there is no traction because your tires (OEM or otherwise) cannot grip black ice, messing with the brake pedal isn't going to help you anyway, and your technique of letting off and getting back on the brakes would not be faster than the car can perform itself.

The only condition where non-ABS stopping is superior is dry summer pavement. In those conditions the car will stop quicker if the wheels lock and skid (flat spot be damned).

Otherwise trust the car to do its thing and blame the lack of traction and lack of braking power on ice, which you can somewhat correct by running winter rubber instead of yoko's.

Last edited by Zeeper; 01-02-2013 at 04:04 PM.
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Old 01-02-2013, 04:08 PM   #18
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Quote:
Originally Posted by Zeeper View Post
The only condition where non-ABS stopping is superior is dry summer pavement. In those conditions the car will stop quicker if the wheels lock and skid (flat spot be damned).
These guys say the opposite.... http://wikicars.org/en/Anti-Lock_Brakes_(ABS)
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Old 01-02-2013, 04:51 PM   #19
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Quote:
Originally Posted by grubincan View Post
These guys say the opposite.... http://wikicars.org/en/Anti-Lock_Brakes_(ABS)
For every quote there is an equal and opposite quote.

http://www.nhtsa.gov/cars/problems/e...kes/page1.html

The question would be what surface are you driving on? Gravel, snow, ice, dry or wet pavement. The answer will be different for all of them.

In most cases the ability to steer is as important as the ability to stop fast. I've driven a car that would lock its brakes very quickly in slippery conditions (the first car I drove was a 70's Ford Maverick) and it was terrible in the snow, and the rain, because when it locked up you could no longer steer it, and was terrible until my sister totalled it (on a snowy road).

Personally, I prefer ABS. In any case, no driver is going to outperform the ABS so pumping the brakes on a car with ABS is not helpful, and will only increase your stopping distance.

Last edited by Zeeper; 01-02-2013 at 04:59 PM.
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Old 01-02-2013, 05:10 PM   #20
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ABS is great for peeps that don't know how to threshold brake.
ABS is great to allow steering with hard braking.
ABS sucks on ice (all 4 lock, thus no speed differential), gravel & snow (gravel & snow will "wedge" allowing shorter stopping than ABS will allow).

Locked wheels are NOT the best on dry pavement, "almost locked" (high tread slip but still rolling...... a bit) is THE SHORTEST WAY TO STOP!!

VDC will not likely kick in if going straight. Most systems are also tied into the steering angle. Going straight has no steering angle, thus no VDC.

Guys, and gals, all these systems do well when you remember ONE THING, they will do no better than the grip of the tire to the road.
Crappy tires, bad surface, going too frikkin fast will OVERWHELM ANY ABS/VDC system out there.

Do a driving school so you have a little clue.

Please.
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Old 01-03-2013, 10:35 AM   #21
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Quote:
Originally Posted by Zeeper View Post
ABS uses individual sensors on each wheel to regulate the brake pressure for that wheel. But in our cars you cannot separate ABS and VDC.
They have to be compared to each other in order to figure out if the car is moving or not. ie: If the ABS see all wheels are "stopped", it'll assume that the car is at a complete stop; it wouldn't know if the car is still moving. On the other hand, if it sees one wheel is locked while 3 are still moving, it'll know that wheel is locked up, and attempt to "correct" it.
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Old 01-03-2013, 10:39 AM   #22
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Quote:
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Locked wheels are NOT the best on dry pavement, "almost locked" (high tread slip but still rolling...... a bit) is THE SHORTEST WAY TO STOP!!
Very true. Locking the wheel may be a huge misconception; hence why you see a lot of rear-end collisions with long skid marks. I don't know how many have locked up the wheels but you can feel it(locking the wheels usually makes the car feel like it's trying to settle/level out, while near the max threshold you're being pushed into the steering wheel).
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Old 01-05-2013, 01:48 PM   #23
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I may have experience this. I like to think of myself as a skill driver and very defensive. Anyways, while I was going to pick up my girlfriend late at night, 24 hours after our snow storm. The roads were still a little icy but nothing major. I was following a car. I was going about 45 mph. I am pretty sure they were a novice drive as they braked on an icy bridge. They were about 100 feet or so in front of me. I begin to brake too, lightly. But, when I lightly depressed my brake. The begin...well how do I put this... pulsating as if traction control and abs were kicking in. My car wasn't skidding or sliding. Just going straight. I felt as if the car didn't have any braking power. Well, my car is equipped with the cvt, so I just kicked it down a gear. Luckily I had kept enough distance in front of me to avoid any catastrophes. But I did think it was odd the car didn't even slow down.
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Old 01-05-2013, 02:42 PM   #24
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The best solution would be getting snow tire next year or right now. ABS is mostly efficient while you brake & turn at the same time preventing the car going straight because the front wheel is locked.

The EBD was probably working if you car slided straight. The braking distance wouldn't have changed much even with the ABS working. Sliding on ice is evil.
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Old 01-05-2013, 03:21 PM   #25
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About the only thing worse than ABS on ice is no ABS on ice:

http://www.fitfreak.net/forums/2nd-g...se-help-2.html

FYI the long and short of this link is a Honda Fit driver from Alaska asking about disabling the ABS, then a discussion about getting the proper tires, then a confession that he compared his Fit with ABS to some other cars his family drives, no ABS, and they were even worse than the Fit was stopping on ice.

Every situation is different. In slippery conditions tires first, but if you have to choose between ABS and non-ABS you bought the wrong car to begin with. Subaru engineers sell cars equipped with ABS and VDC because they believe they are safer than selling cars without these features.

If you want more flexibility adjusting the various systems, get an STI or some other car.
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