The most common road crash is a nose-to-tail impact caused mainly by a lack of understanding of how to brake properly. We have all seen or heard it and anyone who has been driving for any length of time has probably experienced it first hand - the sickening screech of tyre on road followed by a very solid thump. It's most agonising to be in the stationary car at the front of the queue watching Mr Inattentive about to inflict the front of his car on you....
Being confronted with an emergency situation has one immediate affect - it rapidly raises your heart rate about threefold and fear takes control of your car. Understanding what is about to happen when you jump on the brake pedal is the only way of being able to calmly operate in this situation. A locked wheel will not stop you as fast as a wheel that is rotating with a braking affect. In fact, the best braking happens when the braking effort is being applied to the point just before lock-up.
You only have to watch a racing car on a track to see this first-hand - a lock-up mistake usually results in the car leaving the track or at best running wide in a corner and losing positions to other competitors. The other huge disadvantage of a locked front wheel is that it renders the vehicle out of control. No steering can take place if the wheel is not turning.
The most efficient method of stopping in an emergency is threshold braking, also sometimes called cadence braking.
Threshold braking involves technique and feel. Squeeze the pedal firmly so you get the feel of hanging in the seat belts as the weight of the car transfers forwards. This puts more weight over your front wheels - which is good, because it's the front wheels that do most of the braking. Now that you have a higher grip level to play with, all that is remaining is to keep an even and firm pressure on the pedal over the remainder of the stopping distance.
Knowing how hard you can press the brake pedal before the wheels lock up can only be found out through experience. But you need to understand this - if during an emergency stop you hear the ominous sound of tyre squeal and start to smell smoke, un-squeeze the pedal by a small amount to stop the lock-up and regain control! This is where some finesse is required. Come off the brakes too much, and your (so far) well controlled stop will suddenly speed up and extend the stopping distance that you initially required...
The most important advantage of threshold braking is that it leaves you in control and with the ability to steer around an obstacle. If you let fear take control, the brakes will be jabbed hard not giving time for any weight transfer and so locking the wheels. The result is an extended stopping distance without the ability of the driver to steer. It's for this reason that ABS (Anti-lock Braking System) was invented.
However, it's not enough just to have a car with ABS; it is just as important that you know how to use it to its full potential. Many people have no understanding of ABS when they buy a car so-equipped.
[In fact, some research has shown more crashes occur in ABS cars than those not equipped with ABS! - Ed]
As its name implies, ABS will not allow any of the wheels to lock-up, even if the brake pedal is pushed too hard. This eliminates the "fear factor" taking over in an emergency and - provided it is used to its full potential - ABS is a fantastic system for crash evasion.
Confusion with the use of ABS can however be created when swapping from a manual system to a car equipped with ABS. As explained previously, in a manual system it may become necessary to take the pressure off the brake pedal in order to regain control if wheel lock-up occurs. In an ABS car it is imperative that pressure is kept hard on the pedal despite what you may be feeling through the pedal.
When deployed, the ABS will cause the brake pedal to pulsate or shudder and usually an audible grinding sound will accompany it. These sensations have frequently been enough for the uninitiated to release pedal pressure and have what could have been an avoidable crash. If you ever get to the point where the ABS cuts in, leave the pedal pressed firmly where it is - this is as good as it gets! As the system does not allow wheel lock-up, steering is still possible - so just select your escape route and steer around the obstacle if possible.
As with any driving technique, concentration is the key. Give yourself plenty of room between your car and the car in front - two seconds is usually enough. This spacing can be easily worked out if you count slowly when the car in front passes a roadside obstacle. No matter what your speed, you should be able to count two seconds before your car passes the same piece of roadside furniture. Look ahead as far as possible to give yourself the earliest warning of any impending emergency. And don't fall into the trap of following the tail lights of the car in front - its driver could be asleep!
So that's the emergency stop, but what about just good old smooth retardation on approach to a corner? I guess this becomes more important to the performance driver but the basics are just the same - no matter what level you drive at. Judgement and vision, together with a thorough knowledge of your vehicle's stopping potential, are key factors in successfully negotiating any corner.
When pushing the limits, however, sometimes it's just not enough to be able to stop and turn. In order that you don't risk the chance of a "compression lock-up", you need to be able to down-change smoothly while braking hard. Compression lock-up is caused by the engine spinning at a lower rpm to the drivetrain when selecting a gear. Anyone who has ever driven a manual gearbox car will have experienced some form of clutch slip or drag when down-changing. When the clutch is let out, the drivetrain has to speed up the engine revs to match, putting an additional braking force through the driving wheels. If you are hard on the brakes (at the threshold of lock-up) approaching a corner, a down-change may give enough additional braking force to lock the drive wheels. To overcome this problem, a driving technique called heel/toe can be used.
Heel/toe is directly derived from motor racing but it can - and should - be encouraged for general road driving. Heel/toe is basically matching the engines revs to the drivetrain revs by blipping the accelerator with the side of your foot while also braking and down-changing. A good heel/toe technique starts with the correct positioning of the ball of your foot toward the righthand side of the brake pedal. This allows you to pivot slightly while rolling your foot to the right to allow the accelerator to be blipped. Pedal positioning in all-important for this technique to work properly and some cars are better equipped than others. The blipping should take place just before you let the clutch out after changing gear. The amount that you blip the accelerator will depend very much on road speed and can really only be judged by experience. This technique is difficult to master, but if you get it right there should be no trace of compression lock-up and braking should remain smooth and progressive.
Give it a go - not only is it safer and smoother but componentry such as the clutch plate and the synchros will thank you with a longer life. Be warned though - it will take lots of practice, and on your early attempts give yourself plenty of space as you will probably try to eject yourself through the windscreen!
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