Braking Techniques

Braking techniques - an introduction
ABS
What is the fastest method of slowing down?
What is the best method of slowing down?
Threshold braking
Locked wheel braking
Avoidance braking
Cadence braking
Braking distances
Reaction time
Tyre choice
Stopping distance calculator
Tyre friction levels in the wet and dry

Braking techniques - an introduction

"How much technique can there be to braking? Surely it's just a matter of stamping on the pedal and coming to a halt."

• If you have locked your front wheels, you lose steering control
• The point of maximum deceleration is just before the point of wheel lock (see Figure 1)

If you'd like to experiment with various different braking techniques, please do it on a track or on private land where nobody will be at risk of being run over!

Remember – it's always best to brake hard in a straight line if possible.

ABS

For more information on ABS technology, please click here.

ABS is a marvelous invention. By rapidly applying and releasing the brakes in pulses when wheel lock is detected, it allows you to both slow down and steer at the same time. All you have to do is hit the brakes hard and watch as you gracefully come to a halt. In cars with ABS many of the techniques listed here will not be relevant (anything that mentions wheels locking), but many racing cars are not equipped with ABS technology so manual braking techniques are still useful for the track.

ABS was first introduced in cars in 1978, and the technology now is far more advanced than when initially launched. For many years it was possible to slow down faster using manual braking techniques, and traditionally racing drivers have preferred to brake manually. Cnventional racing wisdom tends even to suggest that ABS is not the most efficient method of braking. Today, however, in many real world conditions ABS both prevents wheels from locking and also slows you down quicker than any manual braking technique, especially on wet or slippery roads.

What is the fastest method of slowing down in ideal conditions?

The following list shows the quickest methods for an experienced driver to slow down in high grip conditions. Braking efficiently in the wet is much more difficult, and in this case ABS may well be the quickest.

1. Threshold braking 2. Locked wheels (in the dry) 3. ABS (may be quicker in slippery conditions) 4. Cadence braking 5. Parachute

However, just because a braking technique isn't the quickest to bring you to a halt doesn't mean it isn't shouldn't be used -cornering ability while braking also needs to be considered. Locked wheels do not permit steering so this is only an option when you have a clear straight line ahead of you, however ABS equipped cars and the cadence braking technique both allow you to steer at the same time.

Which is the best technique for slowing down?

This depends on what you're trying to achieve. On the track drivers should aim for threshold braking, however even the best drivers in the world occasionally lock up wheels, and it is at this point the decision needs to be made whether to use cadence braking (if ABS isn't fitted), or reattempt threshold braking using slightly less pressure. In general, locked wheel braking should be avoided where possible, as it does not allow steering control to be maintained.

Threshold braking (ABS and non-ABS cars)

Threshold braking is the best strategy to adopt to gain maximum braking performance on tarmac. As stated above, the point of maximum deceleration is found just before the point of wheel lock (Figure 1), so it makes sense to try and keep the braking pressure just before this point. Practically, it's often very difficult to know exactly the point at which wheels will lock as many factors are at play such as tarmac conditions, tyre choice, brake temperature etc.

Figure 1: Brake pressure vs deceleration

So, unless you're a professional racing driver, the best strategy to adopt is to best to brake hard, and if you find some wheels are locking, slightly releasing the brakes and then reapplying with marginally less pressure. As you learn how your car behaves in these conditions you'll get better at judging the pressure needed for maximum deceleration.

Locked wheel braking (Non-ABS cars)

Ok, so locked wheels aren't quite as good at slowing you down as the threshold braking technique. However there are certain situations when it's very difficult to maintain braking without locking wheels, such as on wet roads.

In this case, sustained wheel lock might not be as bad as you might think. As long as you are heading in the right direction locked wheels will slow you down effectively, but remember that you'll be unable to steer. Which leads us onto the next technique….

Avoidance braking (Non-ABS cars)

"So, I'm on an icy road, going too fast (I'm sorry, but it's a bit late for that now!), I've slammed on the brakes, and now I'm hurtling towards a tree!"

Well, you've been silly, but all may not be lost. Keep the wheels locked for as long as possible to scrub off speed, and while you're doing this, apply a small amount of steering lock (quarter of a turn is a good starting point). Now, release the brakes smoothly and you should find that steering starts to work again. This may be enough to get you round an obstacle. Keep applying and releasing the brakes at points where it is suitable, using small steering movements, or you'll risk understeer or oversteer. This technique works equally well in good conditions at speed, but really should only be used as an emergency procedure.

The illustration above shows avoidance braking at work. Coming off the brakes allows you to steer round the cones, if the wheels had remained locked the car would hit the cones, no matter how much steering was applied.

Cadence braking (Non-ABS cars)

Cadence braking is a braking technique for very low grip surfaces such as an icy road - essentially applying and releasing the brakes rhythmically in order to get a compromise between steering and braking performance. As you apply the brakes, the wheels will tend to lock up, slowing the car but preventing you from steering. As you release the brakes you regain steering control and can keep the car pointing in the right direction.

Attempting to use cadence braking on a good grip surface at speed will result in weight transfers which can unsettle the car, possibly resulting in oversteer – the last thing you need when trying to turn a corner. Not a technique to adopt for fast driving on good grip surfaces!

Braking / stopping distances

If you go out to learn just one thing about your car, try to get to the point where you instinctively know what the stopping distance will be for different speeds at maximum braking effort. Quoting figures are mostly useless in real life situations, this is something that needs to be a split second decision, not a calculation.

Figure 2: Braking distance vs speed

A real-life example:

Ariel Atom 2 300BHP Supercharged 100-0 = 3.8 seconds = 169.9 metres
Source: Autocar Magazine 0-100-0 tests

This figure is plotted in Figure 2 in red. As you can see it comes under trend line illustrated by the Highway Code, but this would be expected for a performance car that weights as much as a small fish.

Reaction time

• Racing driver left foot braking: 0.2 – 0.3 seconds
• Fully aware of braking point: 0.70 to 0.75 seconds to apply brakes
• Unexpected but common signals: 1.25 seconds
• Surprise braking event: 1.5 seconds

Tyre choice

Tyres have different breadths of capability. Dedicated slicks are good in the dry, but poor in other conditions. A general purpose tyre will perform well in many different conditions as shown in FIgure 3 below. Wet tarmac is less predictable than in the dry, however with the right tyres, good braking performance is possible. Remember to be very careful the first few times you approach a corner to recalibrate your braking points.

Figure 3: Tyre grip levels in different conditions

Stopping distance calculator:

Static coefficients of friction for tyres: