[overcoil]

Have an ice storm here in Maryland and running summer tires. The description below from a driving handbook from Vic Elford, I thought, was excellent technique.

Even with anti-lock brakes, when braking on sheer ice, it may be helpful to pump the brake pedal. If not pumping then repeated applications at a rate you feel prudent.
The theory being: the moments between having a rolling tire and locked under braking is the period when the tire is slowing with good road contact. If you can produce as many if those "slowing" periods between ROLLING and LOCKED then you can reduce speed quickly.

Many times on ice there is such low friction between tire and road the ABS won't activate because it thinks the wheel is stationary.

There are times when a locked-up wheel, will create a wedge of debris like gravel or even snow, and that wedge will slow the car. Sheer ice though, will probably not build up a wedge.

Anyway, drive safe.

[ska///235i]

Pumping brakes are pre-abs

Slam on the brakes with abs and it pumps for you

[overcoil]

Originally Posted by ska///235i

Pumping brakes are pre-abs

Slam on the brakes with abs and it pumps for you

If your on ice - ABS may not work, with no friction and all the wheels stationary sliding on ice, there may be no ABS activation. That is why pumping the pedal or on/off application of the pedal, may be the quickest way to slow a car with ABS on ice.

The premier benefit of ABS is you just about eliminate the chance of flat- spotting a tire on a dry road, and you bring in steering. However on ice - ABS may increase braking distance, ABS may not activate. You can watch video of ABS outfitted cars sliding into one another on ice, one reason being prolonged braking distance and sometimes that is due to an ABS system failing to identify that a car is moving.

[gaijin]

Our BMWs are equipped with DSC (Electronic Stability Control (ESC) mandatory in US as of 2012).

It provides:
- correcting impending over-steering or under-steering;
- stabilizing the car during sudden evasive maneuvers;
- enhancing handling on gravel patches e.g. road shoulders;
- and improving traction on slippery or icy roads.

[overcoil]

This is the quote from the Vic Elford book which in certain situations may be helpful

[angelbones]

This is against everything I've ever seen, read, or heard about ABS over the last 20 years. You should never pump the brakes if you have ABS. That is, unless you can pump faster than the computer. In other words, I don't trust this fable. Sorry.

[overcoil]

Originally Posted by angelbones

This is against everything I've ever seen, read, or heard about ABS over the last 20 years. You should never pump the brakes if you have ABS. That is, unless you can pump faster than the computer. In other words, I don't trust this fable. Sorry.

It's really the only time you should cadance brake ABS - in extreme ice situations.

[ska///235i]

Driven in New England weather for over 20 years and I can tell you pumping ABS will NOT work on icy or whatever the road condition is

Its the tires that slide on ice

[krhodes1]

Possibly useful on older cars where there was no stability control system.

Modern ABS/Stability control are much smarter - the computer knows the car is moving, so even if you did manage to lock all four wheels on ice, it is not going to let them stay locked.

[tke743]

Guys, I inadvertently tried this last night (ice in father in laws driveway after freezing rain, worst case scenario.) I can confirm that if there is no friction then the ABS does not activate at all. The car thinks it has stopped even in the case where I was doing a solid 5 mph. ABS works by detecting lockup as a differential between the wheels. If all wheels have zero grip, then it thinks you have stopped.

[threepac3]

Originally Posted by ska///235i

Driven in New England weather for over 20 years and I can tell you pumping ABS will NOT work on icy or whatever the road condition is

Its the tires that slide on ice

SO you've never had that situation where you're only going 10~20 mph and trying to stop smoothly; yet ABS activates nearly putting you in an intersection? ABS is a pretty static system. If it detects locking it will activate? No if ands or buts about it.


~3pac3

[335BOY]

Try Threshold braking. I do that on some surfaces and it does reduce stopping distances. Pumping ABS doesnt really make sense.

[tke743]

Originally Posted by 335BOY

Try Threshold braking. I do that on some surfaces and it does reduce stopping distances. Pumping ABS doesnt really make sense.

Agreed, that is what I had to do on the father in laws ice-rink. (aka his driveway).

[overcoil]

Originally Posted by tke743

Agreed, that is what I had to do on the father in laws ice-rink. (aka his driveway).

I thought you were my friend. Now your siding with my foe

[foamie]

There is some merit to this advice which apply to very specific circumstances.

ABS systems will only be active after you achieve a certain speed, IF you slow down to a the point that ABS is not active then this technique helps. It MAY even activate the ABS system. The driveway situation described by tke743 illustrates this perfectly.

One of the solutions to this problem is not to drive when the roads are covered in ice since traction is almost non-existent on icy roads even with winter tires (which I use) and even if you are the best driver in the world, but this is obviously not practical. The most workable solution is to use "studded winter tires" (metal studs if allowed and rubber studs if metal studs are illegal), if these are legal in your state.
Here is a link to states and their laws on studded tires: http://drivinglaws.aaa.com/laws/studded-tires/

I hope this helps and everybody stay safe

[Killramos]

Our cars have accelerometers in them as part of DSC... They know when they aren't stopped.

I have had my car on ice (lake) and with full brake force the ABS is indeed working. Same is true of any modern vehicle that i have ever driven...

[tke743]

Originally Posted by ScottSinger

I thought you were my friend. Now your siding with my foe

I'm everyone's friend, but I ran into this yesterday and limit was the only option. Especially when the limit is almost zero. This was an inch of smooth ice with new rainwater on top. Near zero traction and that was with snows.

Originally Posted by Killramos

Our cars have accelerometers in them as part of DSC... They know when they aren't stopped.

I have had my car on ice (lake) and with full brake force the ABS is indeed working. Same is true of any modern vehicle that i have ever driven...

I think you miss-understand what an accelerometer does. There is zero acceleration when you hit a zero traction issue with the brakes locked. To the accelerometer the car is stopped, even though it is still moving.

This was worse then a dry ice surface on a lake. This was enter slow at 5 mph and even with limit braking attempts I slid over 100 feet. I've never hit anything like this before and it is probably a once in a lifetime issue, but it was illustrative of the discussion here.

[astroteg]

Just took the 2 day BMW driver's school... Regardless of road conditions, if you need to stop the car, give it full brakes and let ABS (and DSC) do it's thing, remembering to look to where you want the car to go and it will go there.

The worst thing you can do is pump ABS brakes. On the newer cars, ABS can brake individual wheels that are locking up and do so faster than a human. When you pump ABS brakes, you are disengaging braking on all 4 wheels regardless if they're locked up or not.

Instructors also said if it's icy, stay home. Not even winter tires will help.

Can confirm, almost put M235i in an intersection due to ice (ABS was engaged fully and entry speed was less than 20mph). Also got rear-ended when fully stopped on ice - another great reason to stay home when icy - you may be able to stop, but others may not.

[williewonkerz]

Originally Posted by angelbones

This is against everything I've ever seen, read, or heard about ABS over the last 20 years. You should never pump the brakes if you have ABS. That is, unless you can pump faster than the computer. In other words, I don't trust this fable. Sorry.

EXACTLY, this idea is nuts.

I live in a *very* wintery climate where roads are constantly covered in snow pack and ice. I've never had my ABS think "I'm stopped".

[Killramos]

Originally Posted by williewonkerz

EXACTLY, this idea is nuts.

I live in a *very* wintery climate where roads are constantly covered in snow pack and ice. I've never had my ABS think "I'm stopped".

Yup, everyone wants to oversimplify the issue. But the fact is ABS works great for stopping you on slippery surfaces.

I like you live in a very wintery climate. the concept of "not going out when its icy" doesn't work. Period. Should i sit in my house 8 months of the year?

People need to learn how to drive and anticipate ice...

[SmallTownBoy]

Originally Posted by ScottSinger

Have an ice storm here in Maryland and running summer tires.

Summer tires should not be run below about 40°F (+4.5°C) and never on snow or ice. Park the car and call for a ride.

Rarely, if there is absolutely no grip to all four wheels and they lock, then the ABS system may not engage, as if the vehicle is stopped. The ABS senses no differential in rotation between wheels. Then pumping or threshold braking techniques may be needed. This might happen in "black ice" conditions where there is no warning. Otherwise, driving must be adjusted for the conditions. That includes choosing the right tires.

[williewonkerz]

I would be very interested in reading this, so far the abs is working as expected.

I do wonder how speed affects the trigger