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Old 18th January 2010, 04:00   #31
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Originally Posted by adnaps View Post
.... by pumping and releasing the brakes manually , you would actually end up applying the brakes for a shorter period of time and thereby increasing the stopping distance.
Yes! (This ofcourse depends on how fast you pump, and to what extent you pump).


Have thrown together some el cheapo graphs to help explain this further :
(Note - these figures and relative comparisons are all abstract (aka incorrect) - they are just to illustrate the concepts)


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Here you can see that the ABS system comes close to the "perfect" brake-force so many times a second.




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"Pumping" manages the same thing, but only a few times a second (at best) and therefore a LOT more time is spent far away from the ideal braking zone - making it a lot longer of a stop if you pump.
(Note - frequency of pumping and extent of pumping play a role here)
I would not reccomend this in typical driving conditions.
It might help in conditions like snow / gravel where you also require steering input.


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Threshold braking relies on your stig-like abilities to keep the wheels spinning at the point where the tyres have good traction and there is max retardation of speed.

If you're average at this - you will probably do better than pumping, but not as good as ABS.

If youre good (or lucky) at this, you can get good results, perhaps equalling or trumping ABS (unlikely bestcase).

However, its not quite as easy as this graph makes it look!!
Above it just seems like there is a constant brake force being applied, (so simple right? Blame my graph for making it look so easy!) but in reality the brake pressure changes as there are a lot more variables (eg. changing coefficient of friction of the brakepads depending on the speed of the wheel / brake disc, similarly changing friction between the tyre and the road, etc).

cya
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Last edited by Rehaan : 18th January 2010 at 17:24.
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Old 18th January 2010, 11:18   #32
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To me, this might point to the fact that it wasn't a truly reflex / emergency braking. The kind where your heart jumps into your throat.

The fact that you didn't have a collision might mean that you had a split second to evaluate the situation, and chose to go easy on the pedal.

Do you think this is possible?

Let me rephrase that :

If the obstacle was 10 feet closer, do you think you would have pressed that pedal harder ?
Most probably I would not have pressed the pedal any harder, and that is precisely what disturbs me. My instinct would have made me use threshold braking rather than take advantage of the ABS even at the risk of a collision. The problem is that ,my instinct trusts threshold braking more than the ABS due to years of conditioning. I am not entirely sure if Threshold braking can be safely used in practical terms in varying conditions of road surface , tire conditions and drivers response.If possible, I would like to kick my instinct out of the window and rely on ABS, which I believe will offer more reliable and consistent response.
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Old 18th January 2010, 11:33   #33
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You need not brake from a high speed for ABS to kick in. ABS can kick in at speeds as low as 30-40 kmph, if the road is wet or there is gravel on the road. And it can kick in even if you don't press the brake pedal fully.

Just as one can get accustomed to threshold braking, one also gets accustomed to ABS after they experience it a couple of times. The first time it happens you will instinctively pull back your leg.
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Old 18th January 2010, 17:22   #34
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Originally Posted by adnaps View Post
Most probably I would not have pressed the pedal any harder, and that is precisely what disturbs me. My instinct would have made me use threshold braking rather than take advantage of the ABS ....
See thats the part i am not totally convinced about, even though we are talking about you here

I'm under the impression that really sudden emergency braking is more of a reflex of slamming the brakes than a calculated braking effort. This is the situation where ABS will be used by you by default, and it will definitely help to have it rather than locking up in these situations.

What you may have consciously done above is try your best at threshold braking. Which could work well too.

cya
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Old 18th January 2010, 17:42   #35
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But if you drive an ABS equipped car, don't even bother with threshold braking coz ABS does a much better job at keeping the braking pressure on the limit.

With over 20 pulses per sec, you hardly notice the wheels locking and unlocking.

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Old 8th February 2010, 15:31   #36
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ABS or without ABS, to stop a car really quick, apply the right amount of pressure, with the brakes on you could drop a gear or two and leave the clutch. The engine revs also assists you in braking.

Pulling the hand-brake is not a good idea if you are not used to controlling the car when it drifts. This would be the last resort if you have enough space around the car.
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