Discussion
I've made a point on a different thread because its my experience but I'd welcome the views here.
I think we'd all recognise the value ABS has in retaining control of a car under heavy braking when the wheels would lock up.
But is it the quickest way to stop?
Some (including Bosch) claim it is, however I believe that braking just shy of the ABS kicking in is quicker, and if ABS starts to kick in (especially on compacted snow, but also in rain and other situations where grip is low) easing off the brake a little to reduce the ABS activation stops the car more quickly. It certainly seemed to be that way when I had a day at Millbrook and spent some time in the brake test area.
Thoughts?
I think we'd all recognise the value ABS has in retaining control of a car under heavy braking when the wheels would lock up.
But is it the quickest way to stop?
Some (including Bosch) claim it is, however I believe that braking just shy of the ABS kicking in is quicker, and if ABS starts to kick in (especially on compacted snow, but also in rain and other situations where grip is low) easing off the brake a little to reduce the ABS activation stops the car more quickly. It certainly seemed to be that way when I had a day at Millbrook and spent some time in the brake test area.
Thoughts?
It's the quickest way to consistently get the average driver to stop in a reasonable distance, in any given circumstances, while still letting them have steering control.
That's its job.
You probably can outperform ABS in every situation if you're a good enough driver, but it's certainly a good thing for those "Jesus!" [STOMP] situations.
That's its job.
You probably can outperform ABS in every situation if you're a good enough driver, but it's certainly a good thing for those "Jesus!" [STOMP] situations.
It used to be the case that an extremely skilfull and alert driver could stop in a shorter distance using threshold braking than using ABS. However, I don't believe any driver can beat good modern ABS systems - they have the advantage of being able to sense the rotation on each wheel individually and apply and release the brakes to the wheels individually. A driver doesn't have either the mental or mechanical equipment to do that. The modern systems do not completely stop the wheels rotating but relax the braking at the optimum rate of rotation for maximum retardation.
StressedDave, an engineer and expert driving coach who sometimes posts here, tells us that you brake in the shortest distance if you use ABS and let go of the steering wheel (if you are making steering corrections the ABS brain assumes you want to use some of the available grip for steering, and so does not use it all for braking). I have not been able to observe this phenomenon.
In emergency situations, simply press the brake pedal as hard as possible.
StressedDave, an engineer and expert driving coach who sometimes posts here, tells us that you brake in the shortest distance if you use ABS and let go of the steering wheel (if you are making steering corrections the ABS brain assumes you want to use some of the available grip for steering, and so does not use it all for braking). I have not been able to observe this phenomenon.
In emergency situations, simply press the brake pedal as hard as possible.
It depends a lot on the particular system - most of the comments about how amazing they are etc are based on latest generations systems in relatively expensive cars, I don't know if lower budget new systems are as good and I do know for a fact that 5-10 year old systems can get very confused in some situations.
It depends on the surface as well - on a smooth mixed-grip surface the individual wheel braking is a big advantage, on loose gravel or snow they don't do so well.
Its hard to generalise really - with 10 year old ABS on corrugated gravel I can stop the car quicker (and control it more easily) with the handbrake
but I wouldn't expect to beat a recent system on partially ice tarmac.
It depends on the surface as well - on a smooth mixed-grip surface the individual wheel braking is a big advantage, on loose gravel or snow they don't do so well.
Its hard to generalise really - with 10 year old ABS on corrugated gravel I can stop the car quicker (and control it more easily) with the handbrake
but I wouldn't expect to beat a recent system on partially ice tarmac.waremark said:
StressedDave, an engineer and expert driving coach who sometimes posts here, tells us that you brake in the shortest distance if you use ABS and let go of the steering wheel (if you are making steering corrections the ABS brain assumes you want to use some of the available grip for steering, and so does not use it all for braking). I have not been able to observe this phenomenon.
Wow. I don't think I'm brave enough to try that without a huge skid pan!GravelBen said:
It depends a lot on the particular system - most of the comments about how amazing they are etc are based on latest generations systems in relatively expensive cars, I don't know if lower budget new systems are as good and I do know for a fact that 5-10 year old systems can get very confused in some situations.
It depends on the surface as well - on a smooth mixed-grip surface the individual wheel braking is a big advantage, on loose gravel or snow they don't do so well.
Its hard to generalise really - with 10 year old ABS on corrugated gravel I can stop the car quicker (and control it more easily) with the handbrake but I wouldn't expect to beat a recent system on partially ice tarmac.
From my experience, and its probably only practical to implement on fairly low grip surfaces like very wet roads, compacted snow, greasy roads etc, that if you over power the brakes massively such that the ABS is working hard for more than a few pulses, it can be quicker to stop by avoiding the ABS kicking in. I had the good fortune to do this on the brake test section of Millbrook in an Aston Martin - checkerboard road surface drenched in water and you could stop 1-2 car lengths quicker than stomping on the brakes by feeling for the lock up point. I've known it on compacted snow where a friend who lived in Norway for a few years advised very gentle braking as the ABS would simply pulse on and off and couldn't modulate the break pressure enough to cause effective braking. My daily driver is a new shape BMW 6 series so I imagine the brakes are up there with the latest technology (at least in terms of what most cars on the road have) and its the same with that. Tarmac, dry road, warm tyres, you've no chance of beating the ABS. Slippy road where the car just doesn't seem to want to stop, its worth trying less pressure. It depends on the surface as well - on a smooth mixed-grip surface the individual wheel braking is a big advantage, on loose gravel or snow they don't do so well.
Its hard to generalise really - with 10 year old ABS on corrugated gravel I can stop the car quicker (and control it more easily) with the handbrake
but I wouldn't expect to beat a recent system on partially ice tarmac.I thought others may have experienced this but seemingly not. There's lots of comments on ABS v non ABS around, but very little on ABS kicking in and ABS not quite kicking in.
I've managed several times under repeated conditions to show dis-believing instructors that I can stop a car without using ABS in less distance than the ABS does.
But haters gonna hate and I have no way of proving this via the keyboard, so this will probably be my only contribution to the thread.
In light of other posts, I will add these ocassions were some eyars ago now, and it maybe that cutting edge ABS can beat me now.
But haters gonna hate and I have no way of proving this via the keyboard, so this will probably be my only contribution to the thread.
In light of other posts, I will add these ocassions were some eyars ago now, and it maybe that cutting edge ABS can beat me now.
On a perfectly uniform surface with a perfectly balanced braking system it might be theoretically possible to stop slightly quicker from some speeds by holding the brakes just below the point of ABS activation. This assumes that all the wheels will lock up simultaneously and that you are therefore using ~95% of the available grip for all four wheels.
In the real world no surface is that uniform and the weight distribution across the wheels will vary dynamically due to a host of factors (deceleration, cornering, gradient, uneven surface, suspension reaction to bumps etc). The available grip at each wheel will therefore never be exactly the same and will vary dynamically. If you threshold brake to just below the point where ABS activates you are applying ~95% of the braking force that the wheel with the least grip can provide without locking up to all four wheels, the other three wheels will be braking way below their optimum efficiency.
When you just stomp the pedal and activate ABS on all wheels, the system is modulating the brakes individually on all four wheels to provide the most braking force that each wheel can provide. The sum of the total braking force will therefore be greater and you will stop sooner. If you are in a vaguely modern car with ABS and you need to emergency stop, just mash the pedal as hard as you are able and steer round stuff that's in the way. Any trying to be clever and thinking you can outperform the system is foolish and dangerous.
In the real world no surface is that uniform and the weight distribution across the wheels will vary dynamically due to a host of factors (deceleration, cornering, gradient, uneven surface, suspension reaction to bumps etc). The available grip at each wheel will therefore never be exactly the same and will vary dynamically. If you threshold brake to just below the point where ABS activates you are applying ~95% of the braking force that the wheel with the least grip can provide without locking up to all four wheels, the other three wheels will be braking way below their optimum efficiency.
When you just stomp the pedal and activate ABS on all wheels, the system is modulating the brakes individually on all four wheels to provide the most braking force that each wheel can provide. The sum of the total braking force will therefore be greater and you will stop sooner. If you are in a vaguely modern car with ABS and you need to emergency stop, just mash the pedal as hard as you are able and steer round stuff that's in the way. Any trying to be clever and thinking you can outperform the system is foolish and dangerous.
I've had the benefit of testing ABS v non ABS in the same car in an off-road (tarmac runway) location.
If a driver is very competent and giving their full attention to the operation of the brakes, then it is possible to stop in a shorter distance (1-2 car lengths on dry tarmac) with the ABS switched off. It requires the driver to have a very sensitive right foot on the brake pedal, and an ability to threshold brake (holding the brakes just before the point of lock up) right down to stationary.
So yes, you can stop in a slightly shorter distance than ABS, but only if you're a well trained driver with plenty of practice and - crucially - if you're expecting to brake.
In normal circumstances, as others have said, if emergency braking is required, just try to push the brake pedal out through the bulkhead as hard as you can and let the ABS do its thing.
If a driver is very competent and giving their full attention to the operation of the brakes, then it is possible to stop in a shorter distance (1-2 car lengths on dry tarmac) with the ABS switched off. It requires the driver to have a very sensitive right foot on the brake pedal, and an ability to threshold brake (holding the brakes just before the point of lock up) right down to stationary.
So yes, you can stop in a slightly shorter distance than ABS, but only if you're a well trained driver with plenty of practice and - crucially - if you're expecting to brake.
In normal circumstances, as others have said, if emergency braking is required, just try to push the brake pedal out through the bulkhead as hard as you can and let the ABS do its thing.
Two types of ABS systems, passive and active. Passive systems rely on the classic exciter ring and creates a magnetic field in an analogue signal which is later converted in the ABS module. It is a primitive system as the exciter ring has quite a small number of points so accuracy and processing speed are very slow.
More modern Active types create a digital signal and work much more efficiently, especially at low speeds. This is critical for interpreting the point where the wheel physically locks, or releases.
The earlier types gave that distinctive crunching under the brake pedal when it activates. I have found on multiple cars that if going over an uneven surface when braking quite hard, if the ABS did not activate, I would come to a rest a lot quicker than if the ABS did kick in. It would almost give the sensation of 'speeding up' as the braking force decreased.
The more modern active types will be better than what the vast majority of competent drivers can achieve without the system.
More modern Active types create a digital signal and work much more efficiently, especially at low speeds. This is critical for interpreting the point where the wheel physically locks, or releases.
The earlier types gave that distinctive crunching under the brake pedal when it activates. I have found on multiple cars that if going over an uneven surface when braking quite hard, if the ABS did not activate, I would come to a rest a lot quicker than if the ABS did kick in. It would almost give the sensation of 'speeding up' as the braking force decreased.
The more modern active types will be better than what the vast majority of competent drivers can achieve without the system.
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