The ABS discussion thread

[r.verma]

Correct, but irrelevant. Static friction is for moving something from rest. Our goal is the opposite of it.[/quote]

The relative velocity between tire surface and road will be near 0 when wheels are not locked, and that's where static friction comes. Moment wheel locks the relative velocity between tire surface and is huge (= vehicle speed) and hence sliding friction comes in play.

[jaysmokesleaves]

Hi all, I dirve a Landcruiser Prado v6 vx. i put in approx 7-8000 kms every month. comes with abs as standard. 80% skid roads & dusty terrain and 20% hi speed flat out tarmac driving.
my experience with abs:
BRAKING ON TARMAC:

when driven on tarmac if you stand on the brakes in an emergency the wheels certainly don't lock but what happens i feel there is certainly an increase in the breaking distance. i've compared this with a non abs old time prado. attempted slamming brakes full on from a marking point.
braking on the non abs prado.
the old prado( non abs) : tracks straight, almost does a stoppie on the from two wheels, as they lock up big time, and there is brake fade towards as the vehicle achieves a full stop. Then tried quick double pumping the brakes (truckie style) from the same marker. brakes lock slightly quicker, very negligible reduction in stopping distance, absolutely no brake fade observed.
Braking on the the abs prado:
no wheel locking, very uninspiring breaking and approx 2.5 meters increase in stopping distance. no brake fade observed. brake pedal jarring felt.( this jarring effect under heavy braking is felt on almost all the prados ive driven).

breaking with & without off tarmac :
non abs prado:
massive wheel locks depending on traction available, loss of vehicle control, increase in braking distance.
abs prado:
absolutely no wheel lock. allows you to effectively steer while braking, even on turns, allows full control of vehicle at all times. reduction in braking distance.

overview: in my opinion abs is very effective and potentially life saving in conditions where less traction is available( skid roads, dirt roads,wet weather, etc) on plain tarmac under heavy braking in a straight line i think its not good enuf. On tarmac while turning it is very effective since it allows you to control your vehicle . off tarmac its a boon...
allows me to negotiate turns while skidding through with full power on at 120 kph(rally style)... and makes the prado work like magic....would never ever think of doing the things i do without abs. its absolutely confidence inspiring. Yet, more importantly and an often overlooked fact is that the effect of abs can be greatly reduced by poor tire choice.

kudos to new tech. abs zindabad. unfortunately indian car manufacturers do not even offer it as an option except on hi end models. i feel a lot more people will opt for abs as an option on maybe a g4 innova or the safari ex/lx. wonder when that day will come.

[Thad E Ginathom]

Apparently I don't understand the term brake fade.

How can it happen if the wheels are already locked?

[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.

[jaysmokesleaves]

brake fade to me means... that towards the end of the braking manuovre you lose pedal pressure as well as you feel the callipers are gripping but wheels are still moving and the vehicle does eventually come to a halt.

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.


t as i mentioned in my post its not an 'impression' that abs will shorten braking distance. It does and it does not. We measured the distance using markers(unfortunately dint have access to long measure takes)
And yes there is no dis agreement on the control aspect. ABS helps & is felt most during times of minimised / loss of traction allowing you to manouvere while you brake without locking up. The tests we did as mentioned in my post were done using similar vehicles with negligible difference in GVW's. both maintained in pristine condition.

Another point i wish to make is that for an enthusiast its good to know that his/her vehicle has features like abs , vsc, trc, etc... but its imperative for them to understand how these features work. I will discuss this in another thread. thanks.

__________________

[anupmathur]

Originally Posted by vikram_d

Why does everbody have the impression that ABS will shorten braking distance. IT WILL NOT.

For the same reason as everybody having the impression that 4WD means more power!

[Sreenivas]

Originally Posted by sanchits

guys...dont forget..ABS comes with EBD...electronic brake force distribution...so you say the breaking distance is increased, i dont agree to this, cause if the ABS decreases pressure on the brakes....the EBD takes care of it, that optimum pressure is applied to all the wheels and reduces the stopping distance. i own a swift zxi and honda civic, and trust me even in normal breaking, the EBD does a great job and really shortens the breaking distance. ABS coupled with EBD also does a great job to regain control on the car after hard braking.

ABS works well only on all wheel disc brakes, therefore in swift zxi, i t doesnt work very well as the rear wheels try to lock up being drums.

Hi Team,
sanchits has made a point that ABS work good only with all wheel disk, 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 ? (is this a money saving factor for the car Manufacturer)

Thank you

[d_himan]

I own a Swift Vxi non ABS. The other day, I was driving my uncle's SX4 Zxi hard on the East Coast Road. A couple of lambs decide to cross the road when I was at around 150 kmph. I slammed the brakes - from an earlier not-so-pleasant experience of mine in the Swift, I got the instinctive feeling I was in for a hit (I know the theory - pump the pedals/use engine braking etc. etc but I reckon unless you're trained, you can't remember at that critical moment). The ABS worked beautifully - I could feel 'pumping' vibrations on the brake pedal and it came to a halt without a screech inches away from a running lamb. Marvelous. I am now furious with myself for not ordering ABS in my VXi.

Didn't like the driving experience of the SX4 though - I love revvy petrols and this one's a bit too gruff for me.

[Thad E Ginathom]

You were doing 150 on the ECR?

:(

[n_aditya]

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.

Sorry Vikram. I dont understand this. I'm confused now. I remember you "late braking" when we rode in your swift last time I was in blore. If braking distance is not reduced isn't late braking disastrous?

Thad : I've done 165kmph on the ECR during one of the Chennai meets to Mahab's. No one believed me that i could redline to that speed in 3rd and I proved it could be done. This was on the long straight before Muthukadu. But thats a one off incident. I very very rarely drive that fast.

[Sreenivas]

Can someone put some light on my question please

[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.


ABS works to release the brakes everytime wheel lock is detected. This is independent of whether the vehicle has disk brakes or drum brakes.
Inexperienced drivers are expected to react to an emergency braking situation by standing on the brake pedal. The ABS system has been designed to protect these idiots from themselves. The consolation is that the inexperienced driver who stands on the brake pedal can still steer because ABS prevents him from locking his wheels in panic.

However, on a loose gravel surface, by preventing the wheel from locking, ABS can actually increase braking distance and contribute to an accident.

I speak from personal experience, having driven many varieties of car over 27 years, and in a dozen countries. My only accident ever was in an ABS-equipped Buick, because it refused to lock the wheels in an emergency on a gravel surface!

Ram

[jaysmokesleaves]

Originally Posted by ram

ABS works to release the brakes everytime wheel lock is detected. This is independent of whether the vehicle has disk brakes or drum brakes.
Inexperienced drivers are expected to react to an emergency braking situation by standing on the brake pedal. The ABS system has been designed to protect these idiots from themselves. The consolation is that the inexperienced driver who stands on the brake pedal can still steer because ABS prevents him from locking his wheels in panic.

However, on a loose gravel surface, by preventing the wheel from locking, ABS can actually increase braking distance and contribute to an accident.


Ram

Your observation is right when you mention braking with abs on gravel.
Ive almost run off the road into ditches on a few occassions since the abs wouldnt let the wheels lock in my prado. Braking distance is greatly increased.
But conversely abs has also been designed not only to protect inexperienced idiots from themselves but also to protect experienced drivers from being idiots in many cases while allowing skilled drivers to exceed themselves by pushing their own & the vehicles limits.

[Thad E Ginathom]

At long last I understand brake fading. Thanks Ram

And I also better understand the superiority of all round disks.

I think a lot of those idiots we're discussing think that ABS removes limits! Still, I guess that helps to remove a few idiots!

(and I guess that in any group of motoring enthusiasts there are going to be individuals that sometimes drive too fast, and other individuals that express disapproval )

[Surprise]

Originally Posted by d_himan

I know the theory - pump the pedals/use engine braking etc. etc but I reckon unless you're trained, you can't remember at that critical moment

After getting to know about this engine braking, have been practicing on day to day driving [i.e everytime I slow down, gears down+slight braking) ].

But it never struck to put the gear down or pump the brakes during emergency braking as our eyes and mind are glued to interfering object.