I would like more information on ABS

Cone_Junky wrote: It just needs to see one or more wheels spinning slower than the others. Doesn't mean that that wheel is locked up, just spinning a few MPH slower than the others. As mentioned, the newer systems (like in your Audi) also use yaw sensors and brake line pressures to determine when to interfere.

All this, and it gets more complicated by many newer systems using the ABS as a way to get dynamic brake bias, to prevent lockup in the first place.

Best adhesion is generally around 10% slippage, give or take a few percent, so if they system works fast enough, they're going to try to pre-emptively reduce braking when wheel speed differential gets beyond that.

(If you want fun, drive an old GM with ABS-IV in snow and lock the rear wheels with the handbrake, then apply the foot brake just enough to turn the brake lights on. The ABS will go completely spastic and then just give up.)

mazdeuce wrote:

carbon wrote: Does 42 psi sound a little high to anybody else?

Yes, that's rallycross anti de-beading pressure right there.

Not really. I've seen debeads on snows where the remaining front tire was at over 50psi... and 44psi for rally tires.

It goes along with what I've been thinking all along, if you're going to debead, you're going to debead, no matter what your tire pressures are.

AngryCorvair wrote: - @ HappyAndy: The only ABS systems that can apply higher than driver's command are those which are also equipped with a "Panic Brake Assist" feature, which senses the rate at which pressure was initially built by the driver's command, and if that pressure rise rate was above the "Panic Brake" threshold calibration, the ABS pump is instructed to build sufficient pressure to cycle ABS on all channels, until the driver reduces their input to the pedal.

What about the Ford systems with the electric valve in the brake booster? I know they use that for certain levels of stability control.

ABS pump? We don' need that, we'll just apply the brakes with the master cylinder!

AngryCorvair wrote: sorry man, but the ABS is not to blame in either of your scenarios.

Drive a GM with rust forcing the speed sensors away from the tone ring. Happens in about three-four years up here. The sensor is too far away to get a good signal at low speeds and the ABS activates.

I had one truck that would. not. stop. if you were braking lightly through that range. If I didn't throw it into Reverse to stop the truck, I would have run into a wall.

Why weren't the rear brakes sufficient to stop the truck? Rear disks, which always sieze into uselessness in a short period of time.

I guess I'm confused as to how debeading pertains to this discussion. I was referring to proper running pressures for daily use, to maximize grip without accelerated wear. When I'm worried about losing a bead, I just run these. <img src="" />

That what I was talking about, although not specifically Ford. Stability and traction control can do stuff when your not on the brakes, and uses the brakes to do it. Am I completely wrong?

Knurled wrote:

AngryCorvair wrote: - @ HappyAndy: The only ABS systems that can apply higher than driver's command are those which are also equipped with a "Panic Brake Assist" feature, which senses the rate at which pressure was initially built by the driver's command, and if that pressure rise rate was above the "Panic Brake" threshold calibration, the ABS pump is instructed to build sufficient pressure to cycle ABS on all channels, until the driver reduces their input to the pedal.

What about the Ford systems with the electric valve in the brake booster? I know they use that for certain levels of stability control. ABS pump? We don' need that, we'll just apply the brakes with the master cylinder!

What you experienced was a stack-up of (1) reduced grip on one front corner due to the space-saver, combined with (2) more front weight and (3) less rear weight due to heading down a steep hill. your situation reduced your rear vertical force, which limited how much braking the rears could do. your space-saver limited how much grip you had on that front corner. End result is reduced braking, for sure, but can't be blamed on the ABS.

Your assertion is that i still had 3 fully functioning brakes, and my assertion is that i've done enough driving (especially in messed up cars, in my career as an auto tech) to tell you that wasn't the case. I dont know the specifics of the ABS on that particular vehicle (i dont even remember what it was, but i THINK it was an early 90s Corsica).

As for the entire rest of your post: you missed an entirely critical point out after pointing it out yourself. One of my front tires was sitting on top of a piece of sheetmetal. It didn't just have reduced longitudinal traction, it had NO traction. Very similar situation to how kids used to put lunch trays under their tires and go sliding around. It's not hard to imagine a car understeering if one front tire fell completely off; same effect.

My assertion that it is the ABS systems fault is based on the idea that if the ABS system saw that that wheel was locked up, whatever it was doing to reduce braking force was clearly not sufficient to allow the tire to roll off of that piece of metal. I know you cant design around every situation but i would think it is POSSIBLE to design a system that would let the tire roll off that piece of sheetmetal without requiring me to give up on braking entirely via the pedal (which is what i did before regaining control). Clearly there is some minimum braking action designed into the system that was still too high for that particular situation.

carbon wrote: If the tire has never breaks grip, it never has to regain traction, in the time that the stopped wheel is struggling to regain grip, the tire that has traction is slowing the vehicle, building temperature (and thusly increasing grip), and loading (increasing grip). I dont deny that some of the new abs systems are impressive, but they dont trump physics. Like I said in my original post, dont take my word for it, test different methods for yourself, see what works best. Another thing that is commonly a factor in long stopping distances with abs is that the driver senses abs activation and decreases pedal pressure, releasing pressure on the corners that have grip, increasing stopping distances.

i guess i should have a signature block for these topics:

ABS / TCS / ESC Development and Validation Engineer since 1993

Vigo wrote: My assertion that it is the ABS systems fault is based on the idea that if the ABS system saw that that wheel was locked up, whatever it was doing to reduce braking force was clearly not sufficient to allow the tire to roll off of that piece of metal.

my imagination sucks today, because i can not imagine a situation in which a properly functioning foundation brake system augmented by a properly functioning ABS could not get that tire rolling again. we can dump enough pressure to get a 31" diameter pickup truck tire rolling again when it's been locked up on ice.

i'm not saying it didn't happen. i'm saying we don't have enough data to explain what happened.

wait, that's not entirely true. i am saying it didn't happen exactly and completely the way you've described.

HappyAndy wrote: That what I was talking about, although not specifically Ford. Stability and traction control can do stuff when your not on the brakes, and uses the brakes to do it. Am I completely wrong?

Knurled wrote:

AngryCorvair wrote: - @ HappyAndy: The only ABS systems that can apply higher than driver's command are those which are also equipped with a "Panic Brake Assist" feature, which senses the rate at which pressure was initially built by the driver's command, and if that pressure rise rate was above the "Panic Brake" threshold calibration, the ABS pump is instructed to build sufficient pressure to cycle ABS on all channels, until the driver reduces their input to the pedal.

What about the Ford systems with the electric valve in the brake booster? I know they use that for certain levels of stability control. ABS pump? We don' need that, we'll just apply the brakes with the master cylinder!

i forgot about those "active booster" systems!

• @ Knurled, thanks for the reminder.

• @ HappyAndy, because we were talking about ABS, i was only thinking of ABS. you are correct that TC and ESC can build brake pressure without driver brake pedal input.

AngryCorvair wrote: i guess i should have a signature block for these topics: ABS / TCS / ESC Development and Validation Engineer since 1993

Why, so everybody knows how berkeleying ancient you are? 1993, isn't that about when they started using hydraulics and stopped using cables?

Bryce

wait, that's not entirely true. i am saying it didn't happen exactly and completely the way you've described.

Well then you've lost me. I've described as accurately as i can without diagrams and such.

For the record, i'm not anti-abs by any stretch of the imagination. I just sympathize with some people who have said that ABS has done very counter-productive things in certain circumstances. And yes, typically those are the bottom of the barrel systems. A really good system is like magic awesome sauce but not every car (especially going back 10 or more years) even had a system you could call 'good'.

AngryCorvair wrote: - @ HappyAndy, because we were talking about ABS, i was only thinking of ABS. you are correct that TC and ESC can build brake pressure without driver brake pedal input.

From where I sit, it's hard to separate those mentally since it's all the same system or at least heavily integrated with the rest of the active handling. Good points.

Maybe if we called it "Banned F1 Technology" then people would be all for it?

Vigo wrote:

wait, that's not entirely true. i am saying it didn't happen exactly and completely the way you've described.

Well then you've lost me. I've described as accurately as i can without diagrams and such. For the record, i'm not anti-abs by any stretch of the imagination. I just sympathize with some people who have said that ABS has done very counter-productive things in certain circumstances. And yes, typically those are the bottom of the barrel systems. A really good system is like magic awesome sauce but not every car (especially going back 10 or more years) even had a system you could call 'good'.

Vigo, i am not trying to be argumentative. while not from the government, i really am here to help.

i'm picturing a piece of aluminum siding or similar, say 2 feet long and wider than your contact patch, being run over by your tire while you were braking. the brake force at the contact patch causes the siding to slide on the road, and the brake on that tire simultaneously locks up. ABS dumps pressure, but your wheel won't start rolling again, so the siding just keeps sliding along the pavement, with your tire not rotating, until you release brakes entirely? that's what i can't see happening. there's something missing from the description of the event, or it was in a car that had other braking issues that made themselves obvious while the car was in an ABS event -- like the caliper piston wouldn't retract or the slide pins were no longer sliding, so brake torque was still happening even though the pressure had been released.

i mean, even if the tire was hot and sticky and the contact patch stuck to the piece of sheetmetal while the brake pressure was applied, as soon as the pressure was dumped the tire would try to roll until / unless physically restricted somehow by the sheetmetal. that's really the part i'm struggling with. i mean, we can get dually rears to start rolling again after they've been locked up on ice, just by dumping the pressure to that wheel-end brake.

i'm picturing a piece of aluminum siding or similar, say 2 feet long and wider than your contact patch, being run over by your tire while you were braking. the brake force at the contact patch causes the siding to slide on the road, and the brake on that tire simultaneously locks up. ABS dumps pressure, but your wheel won't start rolling again, so the siding just keeps sliding along the pavement, with your tire not rotating, until you release brakes entirely? that's what i can't see happening.

That is EXACTLY what happened. You've got the story 100% correct. I assume since you cant see that happening, you would be mad as berkeley if it happened to you and cost you your car, maybe a trip to the hospital? I got lucky.

Vigo wrote:

i'm picturing a piece of aluminum siding or similar, say 2 feet long and wider than your contact patch, being run over by your tire while you were braking. the brake force at the contact patch causes the siding to slide on the road, and the brake on that tire simultaneously locks up. ABS dumps pressure, but your wheel won't start rolling again, so the siding just keeps sliding along the pavement, with your tire not rotating, until you release brakes entirely? that's what i can't see happening.

That is EXACTLY what happened. You've got the story 100% correct. I assume since you cant see that happening, you would be mad as berkeley if it happened to you and cost you your car, maybe a trip to the hospital? I got lucky.

how much steering was dialed in at the time, relative to direction of vehicle travel?

AngryCorvair wrote:

Vigo wrote: My assertion that it is the ABS systems fault is based on the idea that if the ABS system saw that that wheel was locked up, whatever it was doing to reduce braking force was clearly not sufficient to allow the tire to roll off of that piece of metal.

my imagination sucks today, because i can not imagine a situation in which a properly functioning foundation brake system augmented by a properly functioning ABS could not get that tire rolling again. we can dump enough pressure to get a 31" diameter pickup truck tire rolling again when it's been locked up on ice. i'm not saying it didn't happen. i'm saying we don't have enough data to explain what happened. wait, that's not entirely true. i am saying it didn't happen exactly and completely the way you've described.

I think properly functioning may play a part in it. I have had 2 Cavaliers and a Malibu and I have felt this problem in all of them. The ABS activates on a slick surface and then you feel like the brakes have released and you will roll on forever. I don't know when the brakes start braking again because as soon as I felt it I lifted off them and then got back on them a bit lighter. I think there are several things at work here. All three cars have been very sensitive to the tires. Cheap tires on the front make them undriveable in the wet. and on the Cavaliers some decent tires became bad at a little over half worn. I leave my snows on year round and that seems to make it much better. In the Malibu's case it also has the worst set of rear drums I have ever seen. I have rebuilt them a couple times with new hardware and such but they still go out of adjustment in about two weeks. In all three cars I think what is happening is that the computer would activate to the front wheels with the idea that the rears are doing their part when in reality the rear brakes are often mostly along for the ride.

Wally wrote:

AngryCorvair wrote:

Vigo wrote: My assertion that it is the ABS systems fault is based on the idea that if the ABS system saw that that wheel was locked up, whatever it was doing to reduce braking force was clearly not sufficient to allow the tire to roll off of that piece of metal.

my imagination sucks today, because i can not imagine a situation in which a properly functioning foundation brake system augmented by a properly functioning ABS could not get that tire rolling again. we can dump enough pressure to get a 31" diameter pickup truck tire rolling again when it's been locked up on ice. i'm not saying it didn't happen. i'm saying we don't have enough data to explain what happened. wait, that's not entirely true. i am saying it didn't happen exactly and completely the way you've described.

I think properly PROGRAMMEDmay play a part in it. I have had 2 Cavaliers and a Malibu and I have felt this problem in all of them. The ABS activates on a slick surface and then you feel like the brakes have released and you will roll on forever. I don't know when the brakes start braking again because as soon as I felt it I lifted off them and then got back on them a bit lighter. I think there are several things at work here. All three cars have been very sensitive to the tires. Cheap tires on the front make them undriveable in the wet. and on the Cavaliers some decent tires became bad at a little over half worn. I leave my snows on year round and that seems to make it much better. In the Malibu's case it also has the worst set of rear drums I have ever seen. I have rebuilt them a couple times with new hardware and such but they still go out of adjustment in about two weeks. In all three cars I think what is happening is that the computer would activate to the front wheels with the idea that the rears are doing their part when in reality the rear brakes are often mostly along for the ride.

FTFY.