ADUK Archive

I am aware that the major benefit of ABS is to retain steering control during heavy brakeing.

I believe that theoretically it should also reduce braking distance but I am told not.

What does the forum think.

I don't profess to be any sort of ABS guru but I would be surprised, in like-for-like conditions, if ABS didn't reduce braking distances.

Without ABS, when finding yourself in that situation where full anchors are required, IMO most/all drivers would be hard pushed to be on that fine line between having maximum braking pressure applied without locking one or more wheels. That's what ABS is designed to do - to keep all 4 wheels on that fine line no matter how hard you stamp on the brakes. Without ABS, you would find that either you don't reach that fine line and achieve maximum retardation or you apply too much and lock the wheels. Either way, you should find that the stopping distance is greater than that achieved under ABS.

Even with ABS, I think you'll find that the first thing a lot of drivers do when the ABS activates and the pedal judders under their foot is to release pressure... and I'd probably include myself under that heading . I have tried jamming on the anchors whilst coming down the road outside our house - empty road, snow and ice, 5mph... The ABS coming on still feels weird...

ABS does not decrease braking distance if you know what you're doing (which I don't claim to). Go back to the Carlimits video posted a few weeks back and you'll see the technique. Just shy of the ABS kicking in is the most efficient point.

ABS does not keep each wheel at that point. It waits until the wheel nearly locks up and then releases it. OK so it does this very fast, but essentially it decreases braking force each time it acts.

ABS doesn't reduce braking distance.

My understanding was that minimal braking distance is reached by locking the wheels, but that ABS is nearly as effective at stopping you while still giving you the ability to steer around whatever obstacle caused you to brake in the first place.

I seem to recall some discussion that said it would be noticeably less effective if you were braking on a loose gravel surface (sort of makes sense, as you'd not build up a bulwark of earth in front of each wheel), but on tarmac roads it's probably as near as makes no difference to almost all drivers.

I get to spend a short time on a track next week understanding the effects of braking systems etc., so perhaps I'll come back with a different answer!

Zebedee wrote:ABS doesn't reduce braking distance.

My feeling is based on sliding resistance being less than resisted rolling resistance.

true blue wrote:My understanding was that minimal braking distance is reached by locking the wheels...

Really..! I was under the impression that as soon as you locked the wheels, resistance reduces and the stopping distance increases. Happy (but surprised) to be corrected if that's not the case...

Mr Cholmondeley-Warner wrote:ABS does not decrease braking distance if you know what you're doing...

I've never tried it, but what percentage of drivers do you think would be able to out-brake an ABS system?

The ones with five feet and four brake pedals are in with a fair chance.

Interesting stuff Dave - thanks.

So what's the answer about theoretical maximum braking being with the wheels locked or just about to lock? (I realise ABS stops the wheels locking to give you steering.)

The number of people who are driving around and have never activated ABS (as part of a lesson) is startling.

Surely it should be demonstrated to learner drivers, and allow them to experience what it's like so when they're in a situation where they need ABS to cut in, they know what to expect.

I for one, never realised ABS makes a noise like a machine gun going off until my dad activated it (somehow, whilst going uphill on a slightly damp surface) on a single track road when we met some twit in a Disco going the other way at the speed of sound.

Also, I know the brake pedal will pulse when you activate ABS, and as Dave has said, you MUST maintain a high pressure on the pedal, etc.
But that's only because I enjoy learning about the various aspects of cars and driving, and I've taken the trouble to read guidances on driving etc.

I'd gladly bet you a tenner that a lot of my friends whom are 17 and driving wouldn't know what is happening when ABS is activated, thus panicking and releasing the pressure only to crash into what they were trying to avoid.

When teaching emergency stops I encourage pupils to activate the ABS if only to get them to know what it feels like.

I remember a pupil a few years ago who would not brake hard enough when practicing emergency stops because a previouse instructor had told her that she should not activate the ABS.

fungus wrote:When teaching emergency stops I encourage pupils to activate the ABS if only to get them to know what it feels like.

I remember a pupil a few years ago who would not brake hard enough when practicing emergency stops because a previouse instructor had told her that she should not activate the ABS.

Then there are the more recent developments, EBD and EBA.
There is an argument for learner drivers to have "off road" instruction to feel the effects of these systems, much like learner motorcyclists have to demonstrate basic handling capabilities.

In fact, learner drivers should be made to have at least one lesson at a track to learn how to maintain control of a car whilst at high speed, and another lesson at a skid pan so they can learn how to keep a car under control if they lose grip in wet conditions.

Also, one lesson which includes a full bore foot down top speed run on a runway, so they have the chance to perform an emergency stop from high speed, so they can see the difference between an emergency stop at 30 mph (which probably wouldn't activate ABS) and an emergency stop from 70/80 mph (ABS most likely activated)

Ultra fast acting and efficient, modern ABS systems easily and repeatably out brake a driver. The view that a driver could beat ABS is anachronistic and was really only true when these systems were fairly basic (10, perhaps even 15, plus years ago).

This is straight from engineers at Porsche and McLaren that I've spoken to. And it is why ABS systems are used in race applications when the regulations allow.

Cheers

stefan einz wrote:Ultra fast acting and efficient, modern ABS systems easily and repeatably out brake a driver. The view that a driver could beat ABS is anachronistic and was really only true when these systems were fairly basic (10, perhaps even 15, plus years ago).

This is straight from engineers at Porsche and McLaren that I've spoken to. And it is why ABS systems are used in race applications when the regulations allow.

Cheers

I doubt anyone here is denying this truth but the thread has, perhaps, moved onto thoughts about how to enable "average" drivers to understand and safely experience these functions in action on their cars.
RTFM, most don't.
How many Audi drivers, whose cars have brake wipe assist, know this?