The ABS discussion thread

[ownerofazkaban]

Could you please provide feedback on this video from Bosch ?
(youtube version)

http://www.youtube.com/watch?v=RMmOAwZysvo

esp. braking distance ?

[Thad E Ginathom]

It's a sales presentation! And an American one, at that.

However, I don't have any problems with the claims made. They are a simple statement of what ABS does, and why we would want it. Being pure sales fluff, they don't spend any time on the circumstances in which ABS might not actually help.

My big problem with this video: in every instance where we see feet hitting pedals, there is one big mistake, and that is, feet hitting pedals. This is a fundamentally wrong driving technique: once the clutch is pressed, there is no engine braking.

On that basis, I'd say that video is dangerous rubbish, and they should be ashamed of themselves. Road safety is too important to leave to the marketing department!

[flyingkolors]

Originally Posted by ownerofazkaban

Could you please provide feedback on this video from Bosch ?
(youtube version)


esp. braking distance ?

I agree with most of the claims made here. But, as Thad E Ginathom puts it, they did not highlight the circumstances where ABS too might not help. Also, IMO, I feel the video missed the point of having ABS with ESP.

ABS will aid in swerving without locking the car, but, to keep the control on wet surfaces, its important to have ESP too.

Originally Posted by Thad E Ginathom

My big problem with this video: in every instance where we see feet hitting pedals, there is one big mistake, and that is, feet hitting pedals. This is a fundamentally wrong driving technique: once the clutch is pressed, there is no engine braking.

Can you please elaborate? Are you saying using the clutch while breaking is a bad practice? Wouldn't the car jerk if you do not use clutch while braking?

[Thad E Ginathom]

Yes, I am saying it is a very bad practice, because you want everything on your side, including the engine. Without engine braking, you have to hit the brake pedal that much harder. They tell me that engine braking interferes less with the car's stability too.

In a normal stop, you don't touch the clutch until you are about to stop, or the engine is about to judder and would stall. In emergency braking, you don't care if you do stall!

[Added_flavor]

One thing I noticed here is the part where two wheels are shown on a slippery surface and two on dry tarmac. Isn't ABS assisted with EBD a necessity for stable braking in such a scenario? Wouldn't the car still Fish-tail if it's only ABS equipped?

Can the gurus elaborate more on ABS with and without EBD?

[DerAlte]

No, it is ABS that prevents fish-tailing.

Plain ABS allows wheels to rotate during braking whenever it detects wheel lock, but does not improve braking. ABS with EBD ensures both wheel lock prevention as well as higher force on those wheels that are braking most. EBD just provides redistribution of brake force to the wheels which are able to brake the most (slipping the least). EBD acts when one suddenly kicks down on the brake pedal in panic.

[Sutripta]

Originally Posted by DerAlte

No, it is ABS that prevents fish-tailing.

I know it's not EBD, but how exactly does ABS keep the car in a straight line when braking on a split mu surface?

EBD acts when one suddenly kicks down on the brake pedal in panic.

Isn't that Brake assist?

Regards
Sutripta

[DerAlte]

1. Well, in this context the ABS doesn't keep it going in a straight line, the momentum does ! The ABS makes sure there are no sideways deflections caused by inequal braking, i.e. the braking of each wheel is proportional to the mu it is encountering. Here Mu is inferred, not measured

2. Similar, but not exactly.
- Brake Assist acts when a the rate of travel of brake pedal exceeds a configured value (signifying an 'emergency' situation - when one 'slams' the pedal). In this condition, assuming that the driver has not applied sufficient force on the pedal, the system increases the braking pressure (from master cylinder) suddenly - thereby increasing the chances of better braking. Other systems like BAS (Daimler), Volvo etc. the brake assist system pre-tensions the brakes (only applies pre-tensioning, but does not automatically brake) so that there is earlier than normal braking action. Brake Assist assumes normal road conditions
- EBD (Electronic Brakeforce Distribution) distributes braking force (effectively modulating the duration for which the brake is on ('duty cycle' ) and line pressure) to those wheels which are encountering higher mu. EBD also varies the front/back braking distribution. Assuming that the normal weight distribution is biased to front, it brakes the front 'harder'. In some cars, the rear is initially momentarily braked harder assuming it takes some time for weight to transfer to front.

[figo_mba]

Once I parked my Linea on the top of mud hill. Now it was not raining when I did that, but when I returned it had rained and I found that I could not walk up the hill. It was very slippery. I somehow made it to the car and now i had to descend the hill.
I came up to the point to actually slide down. The tyres were slipping already. Now I was on the incline and going downwards. I panicked and pressed the brake pedal fully. SURPRISE!!! the car stopped sliding (or Slipping) and in small rotations of the wheel it was rolling down. I was still fully on the brakes (meaning I did not take my foot off the brakes) but the car kept moving slowly and I felt that i had control over the car.
I was under the impression that it was the ABS that helped. But now I am thinking was it the E.B.D ? Does Linea have E.B.D ?

[Sutripta]

Originally Posted by DerAlte

1. Well, in this context the ABS doesn't keep it going in a straight line, the momentum does ! The ABS makes sure there are no sideways deflections caused by inequal braking, i.e. the braking of each wheel is proportional to the mu it is encountering. Here Mu is inferred, not measured

Aah! the very basics: Newtons laws of motion. But unequal forces is exactly what a split U surface will generate, isn't it?

2. Similar, but not exactly.
- Brake Assist ......
- EBD (Electronic Brakeforce Distribution) .......

No issue with what is Ba and EBD, but what is predominant when

Originally Posted by DerAlte

EBD acts when one suddenly kicks down on the brake pedal in panic.

Regards
Sutripta

[Soccerfan]

Originally Posted by figo_mba

Once I parked my Linea on the top of mud hill. Now it was not raining when I did that, but when I returned it had rained and I found that I could not walk up the hill. It was very slippery. I somehow made it to the car and now i had to descend the hill.
I came up to the point to actually slide down. The tyres were slipping already. Now I was on the incline and going downwards. I panicked and pressed the brake pedal fully. SURPRISE!!! the car stopped sliding (or Slipping) and in small rotations of the wheel it was rolling down. I was still fully on the brakes (meaning I did not take my foot off the brakes) but the car kept moving slowly and I felt that i had control over the car.
I was under the impression that it was the ABS that helped. But now I am thinking was it the E.B.D ? Does Linea have E.B.D ?

yes Linea has ABS with EBD

[DerAlte]

Originally Posted by Sutripta

... But unequal forces is exactly what a split U surface will generate, isn't it? ...

The other way around! The objective is to keep the wheel rolling so that inequal braking does not happen. Inequal braking will produce a deflection wherever the wheel locks and the tyre gets a good grip. Prevent that (locking) and there is no chance of a sideways deflection (skid). Sideways skid (fishtailing) need not happen as a rule, it is a matter of circumstances (inhomogeneity in the surfaces).

Originally Posted by Sutripta

No issue with what is Ba and EBD, but what is predominant when ...

I know of BA *and* EBD on very few cars (only the large ones usually) - not that it does not make sense in others. If both are present, BA acts first (improving braking effectiveness with pre-tensioning brakes / higher line pressure); if any wheel skids, ABS acts (safety); then EBD acts (minimizing braking distance).

[Sutripta]

Originally Posted by Sutripta

But unequal forces is exactly what a split U surface will generate, isn't it?

Originally Posted by DerAlte

The other way around! The objective is to keep the wheel rolling so that inequal braking does not happen. Inequal braking will produce a deflection wherever the wheel locks and the tyre gets a good grip. Prevent that (locking) and there is no chance of a sideways deflection (skid).

Hi,
Can't work out why a split U surface will not produce unequal forces (resulting in a couple) when all wheels are being braked to their limits, ABS or no ABS. An explanation will be appreciated.

Regards
Sutripta

[DieselAddikt]

Posted this in Punto Niggles thread as well. But thought i'd get quicker response from here. So just posting the query here as well. Please help.

Just now i happened to drive a Punto Emotion Diesel with just 850kms on the ODO. The car is just 2 months old. We wanted to see how it behaves on high speed braking.

So in a open road, we did a quick 130 and braked a little hard. The ABS kicked in. I could feel it.

But the ABS lights did not go off. The Brake Warning light also came up. The MID showed "EBD Failed - Please read Handbook"

What could this be ? The owner of the car is shocked seeing this. help us.

[ownerofazkaban]

@DieselAddikt
It means, the car is on normal braking functionality only. Get it to auth service centre ASAP, drive cautiously till then.

I was always under the impression that ABS 'always' increases braking distance. Am really surprised by the fact that in normal consition ABS helps reduce stopping distance ?? All manuals talk about sightly increased stopping distance esp, in gravel/loose soil the "locked wheels ploughing thru" is considered better for braking distance.