Does ABS work in reverse?

[Mogul]

It isn’t obviously triggered here…

https://twitter.com/listerlawrence/status/16304876...

(hard to tell the gradient in this clip but it must be fairly extreme.)

[stevieturbo]

ABS does not usually operate below 10mph or so

The trigger setup cannot differentiate what direction of rotation the wheels are travelling.

[E-bmw]

The car was also stopped when the wheels locked, so the ABS sensor (at that point) just thinks the car is still stopped.

[Mogul]

You may have something there.

Odd that the brakes were applied (brake lights came on) the instant that it stopped making forward progress.

No obvious attempt to add power, and not obvious wheel spin (who knows what mode it was in).

Surely the driver could have done more here, even if it was on worn summer tyres…

[Pica-Pica]

stevieturbo said:

ABS does not usually operate below 10mph or so

The trigger setup cannot differentiate what direction of rotation the wheels are travelling.

Where I used to live, it was wet a leafy in late autumn. I used to play about braking firmly to a stop, and the car would slide the last metre as the wheels locked and the tyres slide on the leaves. Also the car (an E36 then) used to make a brief whirring sound as I pulled away. I assumed both were related to ABS only coming in above about walking pace. I seem to recall the handbook had a note about the effective ABS speed.

[E-bmw]

Mogul said:

You may have something there.

Odd that the brakes were applied (brake lights came on) the instant that it stopped making forward progress.

Yes, it looks like the driver allowed the slope to stop the car & then applied the brakes, but the laws of physics took over then & the car slipped backwards with the wheels still stationary.

At least that is what I took from the video.

[TwinKam]

Pica-Pica said:

stevieturbo said:

ABS does not usually operate below 10mph or so

The trigger setup cannot differentiate what direction of rotation the wheels are travelling.

Where I used to live, it was wet a leafy in late autumn. I used to play about braking firmly to a stop, and the car would slide the last metre as the wheels locked and the tyres slide on the leaves. Also the car (an E36 then) used to make a brief whirring sound as I pulled away. I assumed both were related to ABS only coming in above about walking pace. I seem to recall the handbook had a note about the effective ABS speed.

Ironically, the ABS not working below 10mph is designed in to bring the car to a halt in snow (!) ...it allows a wedge to build up in front of the tyre. Clearly doesn't have that effect on sheet ice

[stevieturbo]

Mogul said:

You may have something there.

Odd that the brakes were applied (brake lights came on) the instant that it stopped making forward progress.

No obvious attempt to add power, and not obvious wheel spin (who knows what mode it was in).

Surely the driver could have done more here, even if it was on worn summer tyres…

Yes, if the driver wasn't a dick they'd have made it up the hill. Driving on the iciest bit of the road is just stupid. Moving to the side where there was some actual snow would have massively aided traction.

[Pica-Pica]

TwinKam said:

Pica-Pica said:

stevieturbo said:

ABS does not usually operate below 10mph or so

The trigger setup cannot differentiate what direction of rotation the wheels are travelling.

Where I used to live, it was wet a leafy in late autumn. I used to play about braking firmly to a stop, and the car would slide the last metre as the wheels locked and the tyres slide on the leaves. Also the car (an E36 then) used to make a brief whirring sound as I pulled away. I assumed both were related to ABS only coming in above about walking pace. I seem to recall the handbook had a note about the effective ABS speed.

Ironically, the ABS not working below 10mph is designed in to bring the car to a halt in snow (!) ...it allows a wedge to build up in front of the tyre. Clearly doesn't have that effect on sheet ice

Yes, often used as a Scandinavian technique