The ABS discussion thread!!

[Thad E Ginathom]

A real emergency doesn't give time to change gear.

Just stand on it! But try to remember not to stand on the clutch as well; even in high gears there is some engine braking.

[Rehaan]

Originally Posted by vikram_d

Why does everbody have the impression that ABS will shorten braking distance. IT WILL NOT. The primary objective of ABS is to give you control over the vehicle during emergency braking.

Agreed about the primary objective.
However, ABS does reduce braking distance as well!! (in most cases).

Provided :
1. It is a well designed/top quality ABS system.
2. The road is dry (no snow/sand/gravel etc).

ABS will however greatly increase stopping distance on snow/sand/gravel etc.

Originally Posted by Sreenivas

does that mean the Car (referring to SX4) which has drums on the rear wheels will not be of much use even though it has ABS ?

Please find your answer / continue the discussion in this thread >
http://www.team-bhp.com/forum/techni...ur-wheels.html (Does ABS require disk brakes on all the four wheels?)

Originally Posted by ram

Braking friction generates heat, causing both braking disks and braking drums to expand.

A hot disk expands towards the brake calliper, causing braking to be more effective.

On the contrary a hot drum expands away from the brake shoes, causing braking to be less effective. This is called brake "fading".

Try it with a Fiat or Ambassador. After a couple of high-speed braking episodes, such as when trying to stop a heavily loaded car going downhill, the brakes will fade!

Besides, disk brake rotors, are also fully and nakedly exposed to outside air. So they are constantly cooled, reducing the tendency to stay oversize.

Ram,

Interesting explanation, but i feel like you have only touched the tip of the iceberg. Expansion is not really the most significant cause for brake fade, and would only apply if :
- The drums were not self adjusting (all passenger cars w/ drums these days have self adjusting drums (?)).
- The brake shoes were severely worn out as well.

To add to what you said, the cause of (any kind) of brake fade is always heat
(which is generated when friction is used to decelerate the vehicle).

I would say the most commonly experienced cause of brake fade is due to the heat changing the co-efficient of friction of the braking surfaces.

Think of the co-efficient of friction as the amount of frictional force between two materials. eg. sandpaper-on-sandpaper would have a much higher co-efficient of friction than glass-on-glass.

Now, when it comes to brakepads-on-rotor, the coeffieint of friction typically goes up (gets better) just a little as they get warmed up. (This is also the reason why some racing compound pads need to be brought up to temperature before they start working at their best).

However, once the temperature crosses a certain point, the c.o.f begins to drop rapidly. - Meaning the two surfaces have much less friction (stopping power) between them. This is what causes brake fade.

When you use the brakes a lot for continuous periods (eg. going downhill), it generates a lot of heat, which can push the brakepads etc past their ideal operating temperatures - which causes brakefade.

Always use engine braking when possible : http://www.team-bhp.com/forum/techni...ar-brakes.html (The best way to use the clutch, gear and brakes)


Another cause for brake fade (felt as a spongy pedal) is when the heat from the brakes gets transfered to the brake fluid. This can cause the impurities/humidity/gases in the brake fluid to boil and expand.
Brake fluid in its regular state does not compress easily, and hence is used to transfer pressure from the brake pedal/braking system to the discs very effectively. However, once gasses are present in the brake lines, they can be compressed a little - and hence braking force is not transferred as effectively since the gasses are being compressed as well everytime you press the pedal. This is what causes the "spongy" feel and reduces the effectiveness of the braking system.

You can fix this by doing a brake bleed : http://www.team-bhp.com/forum/techni...-bleeding.html (What is Brake bleeding????)


Yet another cause for brake fade is the gasses that are liberated from the brake pad itself when they are heated, and hence affect braking. This is called "green fade".

...and after typing all that i found this link which says the same thing probably in a more understandable manner!
Check it out :
HEL Brake Lines - Brake Doctor

cya
R

[Ram]

@Rehaan: Thanks for that URL Link.

Green fade seems to be a problem associated only with pads that are so new, they have't been bedded yet.
The author states that, "Green fade can be prevented by bedding in the pads correctly. This is a simple procedure to boil off the resins and break in the pads under controlled conditions..."

Another observation is: The problem of brake fade seems to be more acute in the world of two wheelers -- what with their excessive power-to-weight ratios and low braking surface areas (less wheels available to stop the vehicle). Then most Indian bikes have dimunitive engines, so one can imagine por engine compression braking. This would increase the dependency on the friction brakes, vis a vis, say a Volvo bus, with its Voith hydraulic retarder. BTW, our Volvo buses have ABS.

My four-wheel-drive Mahindra MM540 would struggle to reach speeds above 90 km/h, it had dual circuit brakes and 11-inch drums. In four-wheel-drive on a smooth wet road, engine braking from four-driven wheels was awesome. It was needed because the OEM M+S (mud and snow tires) had poor traction and braking on tarmac. But even in the 540 I have not experienced brake-fade.

The only time, I have encountered brake fade is in a borrowed Premier Padmini, while driving downhill.

[zoomingbhat]

Got This Video Of ABS from BOSCH so am uploading it on Youtube.

YouTube - ABS

There are many thing which we do not really agree!!

[Rehaan]

Originally Posted by zoomingbhat

Got This Video Of ABS from BOSCH so am uploading it on Youtube.

Thanks for uploading that video. My views on a few things :

1. Bosch does make some of the best ABS systems. They are OEM suppliers for BMW and Mercedes and a lot of other manufacturers if i am not mistaken. (?). With ABS systems that arent as good, the results probably wouldnt be as good either.

2. It really irritated me the way the drivers would slam on the brakes AND the clutch right away in that video. Maybe it was to negate any sort of influence the engine braking might have had.
See more on this here : http://www.team-bhp.com/forum/techni...ke-clutch.html (Which is the right Sequence Clutch-Brake Or Brake-Clutch)

3. Notice how their comparissons to non-ABS braking were always with the "normal" braking being 100% lockup. I agree that in a lot of panic situations its near impossible to not lock up for a moment or two, but i dont think this was a realistic/fair comparison. I guess it could be a "worst case scenario" comparison.

4. Notice how they didnt show and driving on dirt roads / snow.
I was once crossing the road in the snow in front of an ABS vehicle that was approaching at about 20km/h and started to brake about 50meters before the stop sign. I could see the ABS not ever allowing the wheels to lock up, and the car didnt come to a stop as well as expected. As a result the drivers face looked like

Originally Posted by zoomingbhat

There are many thing which we do not really agree!!

Im not sure i followed what you meant here?

cya
R

[d_himan]

Originally Posted by Thad E Ginathom

You were doing 150 on the ECR?

:(

sorry to veer off topic...

thad, this was on a hot sunday afternoon after mahabs...absolutely nobody around (didn't know there was a 'silence of the lambs' experience awaiting).

that said, a purple Honda Civic 1.8V flew past me when i was at 150+...

[rkbharat]

I recently bought SX4/ZXi with ABS. Though luckily I had to events to see ABS working, I am very keen to know if ABS is functional or not.

1. How should I do it, without putting unnecessary stress on Tyres/brakes/ABS.

2. Should one check ABS regularly if not put on use.

3. If ABS fails, will the brakes work properly in normal conditions.

[suman]

Originally Posted by rkbharat

I recently bought SX4/ZXi with ABS. Though luckily I had to events to see ABS working, I am very keen to know if ABS is functional or not.

1. How should I do it, without putting unnecessary stress on Tyres/brakes/ABS.

2. Should one check ABS regularly if not put on use.

3. If ABS fails, will the brakes work properly in normal conditions.

Hi Rajiv, Take her to an empty & decent stretch of road, go upto maybe 60 kmph, look in your rear view mirrors, ensure that its empty & slam on the brakes. Keep full pressure on the pedal (no pumping, mind you). If ABS is working, you will feel a violent pulsing in the pedal under your foot (this is normal, don't get worried).

You don't need to check frequently as the ABS warning light will come on when the engine is running if there is a malfunction. Under normal circumstances, when you first turn the ignition on, before you crank the engine, the light should glow briefly & then go out.

[vnabhi]

I haven't had the time to go through this entire thread, but I did have a chance to see how ABS works when I was driving downhill in Hyd city limits. I was following a convoy of cars with a gap of 1 car length and the road was wet from a heavy shower. I was planning to overtake the car in front of me.The speed was around 30 kmph (for those from Hyd, it was the Taj Krishna down road to KCP Jn). All of a sudden the cars in front of me braked hard, and I too, panic-braked (and so did an 800 following me).
That was the first time I was braking so hard on an ABS-equipped Fiesta. I heard a juddering sound and the brake pedal vibrated, but I held on. There was no telltale screech that I was expecting. But I did get a chance to steer left to avoid hitting the car in front of me, and stopped beside his quarter panel (1 foot distance in front of his bumper). In the process, the 800 also missed rear-ending me, as I got out of his way.
But, had it been my WagonR, I perhaps would have got a better bite with the brakes (or am I hallucinating), but the car would have definitely skidded due to wheel lock and perhaps hit the car in front at low speed.

[rkbharat]

Thanks Suman, will try it tomorrow morning on the open stretch in front of Leisure Valley.

Originally Posted by suman

Hi Rajiv, Take her to an empty & decent stretch of road, go upto maybe 60 kmph, look in your rear view mirrors, ensure that its empty & slam on the brakes. Keep full pressure on the pedal (no pumping, mind you). If ABS is working, you will feel a violent pulsing in the pedal under your foot (this is normal, don't get worried).

You don't need to check frequently as the ABS warning light will come on when the engine is running if there is a malfunction. Under normal circumstances, when you first turn the ignition on, before you crank the engine, the light should glow briefly & then go out.

[suman]

Originally Posted by rkbharat

Thanks Suman, will try it tomorrow morning on the open stretch in front of Leisure Valley.

In fact, you can try it at a lower speed also, the important thing is to hit the brakes suddenly & hard & keep the pressure on - no gradual braking

[jalsa777]

Originally Posted by Rehaan

Agreed about the primary objective.
However, ABS does reduce braking distance as well!! (in most cases).

Provided :
1. It is a well designed/top quality ABS system.
2. The road is dry (no snow/sand/gravel etc).

I have an ABS equipped Innova.

I was going at a decent clip, about 100 kmph when my co-passenger suddenly pointed out to a left turn slightly ahead.

I braked hard to reduce speed (did not slam the brakes, but hard enough to reduce to necessary speed).

There was slight gravel on the road,
the ABS cut in too soon and i completely overshot the turn by around 10-15 meters.

i knew the car could brake in time and had much more grip than the ABS assumed.

So, ABS sucks in gravel and low grip situations (maybe rain also)

but whatever it is, it is a life saver for normal drivers (i mean, drivers with no track experience or advanced skill or knowledge)
because they just slam the brakes in emergency and ABS can save lives.

Also, innova's ABS is kinda stupid, once it gets activated at a certain amount of brake pressure, it does not turn OFF when grip improves, untill you release the pressure
i.e. it has not real time-sensing once activated. (i dont know about other systems, i geuss the more advanced systems have these feature)

[kuttapan]

Originally Posted by jalsa777

Also, innova's ABS is kinda stupid, once it gets activated at a certain amount of brake pressure, it does not turn OFF when grip improves, untill you release the pressure
i.e. it has not real time-sensing once activated. (i dont know about other systems, i geuss the more advanced systems have these feature)

That's what you think ! Actually, it cannot work without a real time sensing..Picture this - ABS senses wheel locking up and releases the brake pressure for a moment and applies it again. if the wheel still locks up, it repeats the process. It cannot do away with any of the steps involved.

You are right that the stopping distance increases in slippery situations - in gravel/mud etc it maybe more with ABS. And it is not about the how grip the ABS thinks it has - it is just how fast your wheels lockup - if you have good brakes and no traction, they are going to lock up before you can say - 'There goes the left turn'.

ABS works well my friend - just that you have different expectations from it.

[aaggoswami]

Originally Posted by jalsa777

I have an ABS equipped Innova.

I was going at a decent clip, about 100 kmph when my co-passenger suddenly pointed out to a left turn slightly ahead.

I braked hard to reduce speed (did not slam the brakes, but hard enough to reduce to necessary speed).

There was slight gravel on the road,
the ABS cut in too soon and i completely overshot the turn by around 10-15 meters.

i knew the car could brake in time and had much more grip than the ABS assumed.

So, ABS sucks in gravel and low grip situations (maybe rain also)

but whatever it is, it is a life saver for normal drivers (i mean, drivers with no track experience or advanced skill or knowledge)
because they just slam the brakes in emergency and ABS can save lives.

ABS increases braking distance in wet, snow, gravel surfaces. This is reason why particularly, in Europe it became popular. If they braked hard in snow without abs, the cars used to get out of contorl. So came AbS. Yes they do increase distance, but for the normal driving they are life savers.

[sinhsha]

I have gpt one dzire ZDI fitted with ABS.
The ABS light comes up briefly on ignition on and then goes off. I checked with other dzire zdis and SX4 and found all ABS tell tales like juddering of brake pedal and no tire screeching. But with my car on sudden brake there is no pulsation in the brake pedal and tire do skid putting tire marks on road.
I have taken the car to MASS and they said they cann't find the problem.
Please suggest what to look for and where.