Discussion
Hi,
I got a training dvd which shows that breaking at the threshold of the ASB kicking in is the best method with the shortest stopping distance. (I've been guilty of clutch down too early)....
So how can you tell when you are at the threshold of the ABS kicking in?
Cheers for the advise
I got a training dvd which shows that breaking at the threshold of the ASB kicking in is the best method with the shortest stopping distance. (I've been guilty of clutch down too early)....
So how can you tell when you are at the threshold of the ABS kicking in?
Cheers for the advise
Edited by GTR LUST on Saturday 7th January 00:09
In short, by doing it again and again. There is no fixed pedal position or braking pressure which will cause the tyres to begin to lock up- It is simply the point at which the tyre has exceeded its threshold (the amount of friction it is able to provide in a given condition). It is much the same as in a car which isn't equipped with ABS- once you've exceeded the limit enough times and locked up, you know roughly what you're feeling for. The only difference with an ABS car is that when the tyres lock up (they still do, momentarily), the system backs off the pressure to unlock the wheel and re-applies the pressure until they lock again- the cycle is simply repeated every 'N'th of a second. It is a 'Dumb' system- It does not know when to 'expect' the tyres to lock, but once they do it comes into action. It knows the wheel has locked up because of a reluctor ring in the hub which is read by a sensor- If the sensor doesn't pick up a signal in a certain amount of time, the ABS 'figures out' that the car is moving and that wheel isn't turning.
You'll have to bear with me here, because this is quite hard to explain!
Many people don't understand this very well, but where braking is concerned, maximum deceleration is usually provided when the tyre is turning approximately 10% slower than the vehicle is covering the tarmac- the tyre is in a constant state of controlled slip. It's quite hard to get your head around because people view tyres as sticky rubber things that roll along a surface, when in fact they are 'sliding' whenever the car is accelerating hard, decelerating hard, or cornering. Because of this you can eventually develop a feel for it through the steering wheel and the seat of your pants, and with a lot of practice and a lot of time chasing lap times on the same corners of the same circuit on the same day, you might be able to acheive '10% slip' braking fairly consistently. Of course, you'll have to re-learn it all if it rains, or if someone drops some oil, and it may be completely different from one corner to the next!
So with that in mind, how relevant is all this to road driving? well, as your instructor says, you can pull up quicker by 'threshold braking' than you can by using the ABS, particularly in challenging conditions. If you use a well-serviced car with reasonably equal tyres all round, your ABS should behave fairly consistently- so you just need to be able to get enough practice on a track/airfield day/wherever to become familiar with what this 10% slip sensation feels like in your car. If the ABS cuts in it is no biggie- at the end of the day it still does a pretty damn good job. But by 'beating the ABS' (threshold braking up to the point just before it cuts in) you will make life much more comfortable when and if the snow arrives!
This is very simplistic but I think it's a general gist.
Another consideration is what happens if you're braking and cornering. Obviously a proportion of the tyre's frictional potential is being 'used' to turn the car and a portion of it is being used to 'slow' the car. So effectively your tyre has a lower proportion of it's potential for slowing, and you have to compensate by reducing your braking pressure compared to braking in a straight line.
You'll have to bear with me here, because this is quite hard to explain!
Many people don't understand this very well, but where braking is concerned, maximum deceleration is usually provided when the tyre is turning approximately 10% slower than the vehicle is covering the tarmac- the tyre is in a constant state of controlled slip. It's quite hard to get your head around because people view tyres as sticky rubber things that roll along a surface, when in fact they are 'sliding' whenever the car is accelerating hard, decelerating hard, or cornering. Because of this you can eventually develop a feel for it through the steering wheel and the seat of your pants, and with a lot of practice and a lot of time chasing lap times on the same corners of the same circuit on the same day, you might be able to acheive '10% slip' braking fairly consistently. Of course, you'll have to re-learn it all if it rains, or if someone drops some oil, and it may be completely different from one corner to the next!
So with that in mind, how relevant is all this to road driving? well, as your instructor says, you can pull up quicker by 'threshold braking' than you can by using the ABS, particularly in challenging conditions. If you use a well-serviced car with reasonably equal tyres all round, your ABS should behave fairly consistently- so you just need to be able to get enough practice on a track/airfield day/wherever to become familiar with what this 10% slip sensation feels like in your car. If the ABS cuts in it is no biggie- at the end of the day it still does a pretty damn good job. But by 'beating the ABS' (threshold braking up to the point just before it cuts in) you will make life much more comfortable when and if the snow arrives!
This is very simplistic but I think it's a general gist.
Another consideration is what happens if you're braking and cornering. Obviously a proportion of the tyre's frictional potential is being 'used' to turn the car and a portion of it is being used to 'slow' the car. So effectively your tyre has a lower proportion of it's potential for slowing, and you have to compensate by reducing your braking pressure compared to braking in a straight line.
GTR LUST said:
Hi,
I got a training dvd which shows that breaking at the threshold of the ASB kicking in is the best method with the shortest stopping distance. (I've been guilty of clutch down too early)....
So how can you tell when you are at the threshold of the ABS kicking in?
Cheers for the advise
Why, in normal public road driving, would you want to have the shortest stopping distance?I got a training dvd which shows that breaking at the threshold of the ASB kicking in is the best method with the shortest stopping distance. (I've been guilty of clutch down too early)....
So how can you tell when you are at the threshold of the ABS kicking in?
Cheers for the advise
Edited by GTR LUST on Saturday 7th January 00:09
ABS is a system designed to enable you to brake and simultaneously steer, thus providing you with the ability to, perhaps, avoid a collision.
In other words, it's for the abnormal, not to be used as your default braking method.
However, that being said, your vehicle, NSL road, no one else around, practise braking at increasing pressures. you'll probably be be quite surprised about how hard you have to press the brake pedal before you feel the feedback that tells you ABS has been activated.
Which is why we now have such as EBA, most drivers not being able to really brake hard.
Cheers for the help, I think I get it, I'll just need to preactice a bit more.
When I said I was guilty of clutch down too early, I ment as in clutch down througout the braking :/
I have pretty much mastered Cadence breaking, but it does upset the car's motion, and the threshold braking is clearly a more controlled method of stopping the car in a shorter distance.
BTW, I am doing some track days this year, and trying to learn some new techniques
When I said I was guilty of clutch down too early, I ment as in clutch down througout the braking :/
I have pretty much mastered Cadence breaking, but it does upset the car's motion, and the threshold braking is clearly a more controlled method of stopping the car in a shorter distance.
BTW, I am doing some track days this year, and trying to learn some new techniques
GTR LUST said:
When I said I was guilty of clutch down too early, I ment as in clutch down througout the braking :/
Yeah try to stop doing that! I utterly hate the sensation of braking with the clutch in... Means the engine is basically at idle by the time you have completed your braking, and then you select a gear and drag the clutch up? IME you need to be in the appropriate gear for exiting the corner before you've even turned in, with the clutch engaged.
Classic Grad 98 said:
GTR LUST said:
When I said I was guilty of clutch down too early, I ment as in clutch down througout the braking :/
Yeah try to stop doing that! I utterly hate the sensation of braking with the clutch in... Means the engine is basically at idle by the time you have completed your braking, and then you select a gear and drag the clutch up? IME you need to be in the appropriate gear for exiting the corner before you've even turned in, with the clutch engaged.
Putting the clutch in while braking, and removing the engine braking force will affect the brake balance of the car (for a RWD car it'll throw the brake balance forward, for a FWD car it'll throw it backwards), which is no problem on the road, as you should never be that close to the limit. On track where you want to be right at the limit of adhesion, and possibly trail braking, it could cause an issue though.
As was stated earlier, ABS enables you to brake and steer at the same time in an emergency situation, is is often better to consider it a STEERING aid not a braking aid.
I tried this last winter in the snow with pupils in a car park.
Using threshold braking stopped the car about 10% sooner than relying on ABS, took most pupils about 3 goes to get the hang of it.
I tried this last winter in the snow with pupils in a car park.
Using threshold braking stopped the car about 10% sooner than relying on ABS, took most pupils about 3 goes to get the hang of it.
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