RE: PH Origins: Anti-lock brakes

[anonymous-user]

CraigyMc said:

ABS doesn't shorten braking distances, it elongates them.

But in the real world, with real drivers (ie ones not just unskilled, but unprepared to have to suddenly apply exactly the correct pedal force for a threshold stop, on an unknown road surface, in a panic emergency situation, then ABS massively shortens the effective stopping distance!


Modern systems, that learn the tyre and road friction, and have real time dynamic measurement and control, so they can apply maximum brake force before a loss of stability, will always return at absolute worst, the same stopping distance as a very very very good human driver, and at the same time, maintain steering authority. ABS is banned in F1 for good reason!

[CraigyMc]

Max_Torque said:

CraigyMc said:

ABS doesn't shorten braking distances, it elongates them.

But in the real world, with real drivers (ie ones not just unskilled, but unprepared to have to suddenly apply exactly the correct pedal force for a threshold stop, on an unknown road surface, in a panic emergency situation, then ABS massively shortens the effective stopping distance!

Bit of selective quoting there. Don't forget the bit where I wrote "Overall the case for ABS is conclusive though."

Max_Torque said:

Modern systems, that learn the tyre and road friction, and have real time dynamic measurement and control, so they can apply maximum brake force before a loss of stability, will always return at absolute worst, the same stopping distance as a very very very good human driver, and at the same time, maintain steering authority. ABS is banned in F1 for good reason!

My E90 loses braking totally for about 5m when you hit a pothole on the front nearside hard enough while braking. It's not the only car I've noticed and tried this on (because there's a collapsed drain to reliably try it on!). That modern enough for you?

I will demonstrate this to you personally if you're ever near MK.

I don't plan to pull the fuse on it to see what the retardation would be like sans ABS/EBD on the same test, but it's definitely not going to be *nothing*.

[RoverP6B]

E30 with ABS, really? Mine didn't have it...

I do miss practicing cadence braking, but I'm sure my E39s can do it better than I can.

The only time I can recall ABS actually making itself felt was in my E46 in the snow, there was a noise like a pneumatic drill from under the car as it rapidly jackhammered the brakes... or would that have been traction control trying to cope with the slip?

[anonymous-user]

CraigyMc said:

My E90 loses braking totally for about 5m when you hit a pothole on the front nearside hard enough while braking. It's not the only car I've noticed and tried this on (because there's a collapsed drain to reliably try it on!). That modern enough for you?

I will demonstrate this to you personally if you're ever near MK.

I don't plan to pull the fuse on it to see what the retardation would be like sans ABS/EBD on the same test, but it's definitely not going to be *nothing*.

i drive an E90 too so thanks for the offer of a demo, but i know how they respond ;-)

You say the system "looses braking for 5m" er, ok, then that is the distance over which it is required to "pick lowest" in order to ensure stability is maintained under those conditions. It's not a fault, it's simply what the system has had to do to maintain stability (in this case, yaw stability). Now, as a top notch driver, i'm sure you could cope with the yaw under those particular conditions, a quick dab of oppo, and away you go, no problems. However, the other 900,000 people who'd bought a 3 series, and who would struggle to drive a greasy stick up a pigs a*se, er, no, for them, it's better for the system to prioritise stability over ultimate stopping distance. In fact, in reality, this is really important, because a side impact (after a loss of stability) is much more likely to result in serious injury than a frontal one.

So unless you do an A-B-A test, where you stop, turn round, disable the ABS, and then carry out exactly the same braking event, saying "oh but the system turns off the brakes" is, essentially meaningless.....

[CraigyMc]

Max_Torque said:

CraigyMc said:

My E90 loses braking totally for about 5m when you hit a pothole on the front nearside hard enough while braking. It's not the only car I've noticed and tried this on (because there's a collapsed drain to reliably try it on!). That modern enough for you?

I will demonstrate this to you personally if you're ever near MK.

I don't plan to pull the fuse on it to see what the retardation would be like sans ABS/EBD on the same test, but it's definitely not going to be *nothing*.

i drive an E90 too so thanks for the offer of a demo, but i know how they respond ;-)

You say the system "looses braking for 5m" er, ok, then that is the distance over which it is required to "pick lowest" in order to ensure stability is maintained under those conditions. It's not a fault, it's simply what the system has had to do to maintain stability (in this case, yaw stability). Now, as a top notch driver, i'm sure you could cope with the yaw under those particular conditions, a quick dab of oppo, and away you go, no problems. However, the other 900,000 people who'd bought a 3 series, and who would struggle to drive a greasy stick up a pigs a*se, er, no, for them, it's better for the system to prioritise stability over ultimate stopping distance. In fact, in reality, this is really important, because a side impact (after a loss of stability) is much more likely to result in serious injury than a frontal one.

So unless you do an A-B-A test, where you stop, turn round, disable the ABS, and then carry out exactly the same braking event, saying "oh but the system turns off the brakes" is, essentially meaningless.....

I didn't say my car was faulty. I said this:

WIth all due respect, it's still possible to confuse ABS/EBD by braking over a pothole or similar in the road even with an up-to-date system. In this limited case, ABS doesn't shorten braking distances, it elongates them.

Overall the case for ABS is conclusive though.


Which apparently you're now agreeing with.

[Mr2Mike]

CraigyMc said:

WIth all due respect, it's still possible to confuse ABS/EBD by braking over a pothole or similar in the road even with an up-to-date system. In this limited case, ABS doesn't shorten braking distances, it elongates them.

Of course a half decent driver would have noticed the low traction surface approaching and eased off until over it

[anonymous-user]

CraigyMc said:

WIth all due respect, it's still possible to confuse ABS/EBD

I think we are in agreement, i just disagree with this ^^ bit! The ABS is NOT confused, it knows exactly what it is doing when it releases all the brakes (pick low strategy) on a single wheel intervention...... ;-)


Motorsport systems typically have the stability threshold on an adjustable knob so the driver can make a choice between max stability and max retardation, road car systems are necessarily biased towards stability, because the skills of the driver are so varied and unknowable.