Effective Braking Techniques

The brakes fitted to your car will perhaps be something you take very much for granted. After all, when you recognise the need to lose speed quickly, you just lift off the gas, put your foot onto the brake pedal and the car slows down. Nothing to it is there? However, why is it, when you do that, does the car slow or stop? What’s going on underneath you?

You may not quite have thought of it like this, but when you apply your brakes, even when they are working at maximum efficiency, they will only be able to slow your car at a rate according to the amount of grip available from your tyres. Why? Because the tyres are the only part of your car that is in contact with the ground, and if things were any different, we would all be able to get 100% braking effect 100% of the time, even when driving on ice!

Tyre grip is caused by friction,
and friction between tyre and road is caused by down force

Brakes use tyre grip to slow and stop the car, and tyres get their ability to grip the road from something called friction, which in turn, is provided by down force. A road car gets its down force from gravity, as it is the mass of that vehicle acting downwards onto the road surface that provides tyre grip. Therefore, if you have a car that weighs 1,000kgs, and let us say that weight is evenly distributed within the vehicle, you will have 250kgs of down force acting on each of the four wheels, creating equal friction between each tyre and tarmac.

The problem is you cannot drive a car without there being a constant variation in the amount of downforce applied to any of the four tyres, which of course will vary according to what the car is doing any given time. When you apply your brake pedal, and whilst driving forward, there becomes an increased amount of down force at the front of the car.

The car doesn’t lose any of its overall weight, it’s just there is now a variation in the distribution of the overall amount of downforce available. Whatever the total amount of down force, it all has to be shared between the four tyres.

Why bigger and more powerful brakes are fitted to the front of the car

This is why bigger and more powerful brakes are fitted at the front wheels, as compared to those at the rear. Under braking the front tyres will give you better road adhesion, when compared to those at the rear, so it makes sense to create the most braking force where there is the most tyre grip. With less down force at the rear, any substantial braking going on at that end of the vehicle would easily result in a wheel lock–up situation.

Braking systems fitted to cars, and light to medium weight goods vehicles, are operated by hydraulics via a series of small–bore tubes (brake pipes) filled with fluid connecting the action of the brake pedal to the brake units fitted to each wheel.

To overcome the problem of increased downforce at the front, and decreased down force at the rear, under braking, there is a pressure limiting valve built into the system that will detect the difference between the front and rear loading, and will compensate by adjusting the balance in braking power accordingly to prevent rear wheel lock–up.

How to Get Better Performance From Your Car Brakes

Whilst the effectiveness of the vehicle brakes is limited by the maximum amount of available tyre grip, better braking performance can be realised by applying the brakes in an intelligent manner.

There will be many who have travelled as a passenger in car and perhaps wished they had remembered to bring a surgical collar with them. You know the type of driver? The one who just pokes at the brake pedal, separating your vertebrae every time they slow the car down, or who will leave braking very late so that your eyeballs jump from their sockets due the terrific rate of deceleration. Very often, what should be a gentle process, becomes an eye–popping and rather hurried almost emergency stop.

Rough handling of the car causes accelerated wear
and diminishes your control potential

Apart from being very uncomfortable, and there being an enhanced risk of skidding or control loss, it is quite harmful to treat a car in this way. Think about the stress that type of abuse places upon the suspension linkages, the brake components and even the engine mountings. Yes, the engine mountings — and the gearbox too, for that matter.

Every time you snap the brakes on in a rough manner your engine and gearbox are trying to jump out through your radiator grille in just the same way all that stuff you have dumped on your back seat flies forward onto the floor. Make no mistake, there is a lot of stress going on there.

For the highest level of braking performance, apply them progressively and when the vehicle is travelling in a straight line. Straight line braking ensures the most satisfactory distribution of downforce. Whilst is if not possible under these conditions to give each tyre a whole 25% of what is available, if you can apply the loading over matched pairs of tyres in an equal manner, that is the best compromise you can wish for.

Under braking, you will need to match loading between the front tyres, which means by default you will have matched loading between the rear tyres. By applying the brakes with empathy, you will create maximum vehicle stability under braking and realise the maximum level braking performance for the conditions.

Progressive Braking Gives Better Stopping Power

To apply progressive braking, firstly rest your foot on the pedal and gradually increase the pressure until the desired amount of braking effect is achieved. Once your speed has been reduced sufficiently, the procedure is then completed in reverse, i.e. you release the pressure on the pedal in the same progressive manner.

Braking should be pooh–shaped. That is to say it should be tapered at both ends and fat in the middle. It is amazing how the thought of this creates a much smoother driving technique! Braking should be commenced early to give time for smoothness, but that can only be achieved by good quality distance observation, well–developed anticipation skills and effective advanced planning.

Braking whilst cornering will immediately put the car off–balance, as the front tyres of the vehicle will become more heavily loaded, and because you are steering, the extra loading becomes biased to one front corner. This is one heck of a load for one suspension unit to cope with, and it creates a great deal of extra work for one tyre to have to cope with too.

When brakes are applied in a bend, particularly with front wheel drive vehicles, not only do the tyres at the rear of the car have less down force available, but what they do have becomes unevenly distributed. This makes it even more difficult for the back tyres to grip the road.

Due to the effect of cornering the rear of the vehicle wants to swing out to vertake the front. Applying the brakes whilst cornering can even cause the rear tyre on the inside of the curve to lose contact with the road altogether, as vividly illustrated in this photograph.

Another product of braking into a bend is that due to momentum, the car will be more intent on pushing straight ahead, instead of changing direction as you intended. If you don’t get the oversteer situation, as mentioned above, you will certainly experience understeer.

The Actions of The Average Motorist

Having read this series of articles about advanced methods of driving you will no doubt begin to notice how the general motoring public deal with bends and corners. The usual pattern is to decelerate, brake and to change down through the gearbox, all whilst steering around a bend, completing all these actions at the same time. In fact, the huge majority of drivers will only reach the most appropriate road–speed for a bend, and have selected the appropriate gear, no earlier than the half–way point of completing the bend.

The effect is very unkind to the car, as well as being uncomfortable for anyone on board, because as soon as the foot is lifted from the gas, and⁄or the brakes are applied, the balance of the vehicle changes, as the emphasis on down force becomes biased towards the vehicle front. With steering being applied as well, this will create greater potential for things to go wrong, and not only that, but it knocks hell out of the tyres too.

Drivers who brake into corners will scrub away the outer shoulders of their front tyres and won’t get anywhere near the mileage they could from them. They also accelerate the amount of wear and tear that occurs within other component parts, such as suspension units, causing increased maintenance and repair costs.

The Effective Method in Braking For Bends

The most effective way to deal with braking for bends is to firstly bring down the speed of the car until you are happy it is appropriate to complete the bend you are about to enter, and whilst still travelling in a straight line. Having settled the car to the speed required, now directly select the most suitable gear to provide the necessary response relative to the speed at which you are travelling — again before you start to turn into the bend.

By these means, at the time you begin steering into the bend, you will are travelling at the right speed and with the right gear engaged (we won–t go into the topic of positioning here, as that would over–complicate matters for now).

When you actually take the car around a bend, apply just enough throttle to keep the engine pulling, but without the car accelerating. By these means you will achieve the best situation in terms of vehicle stability, particularly as the loading of down force will be matched between the two tyres along the outside of the curve, and between the two tyres on the inside.

When descending a winding hill, apply firm braking when the car is travelling straight, even exaggerating the amount of speed loss required before the bend is reached, and then apply lighter brake pressure around the curves as required. Also, try to use only one brake application per task, as not only does this form one of the key elements of The System of Car Control, a subject to be dealt with in a later chapter, but it also helps a driver to become more disciplined in searching out actual or potential danger.

Julian Smith
Ride Drive Limited

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Part–1 Effective Braking Techniques
Part–2 How a Car Braking System Works
Part–3 Vehicle Stopping Performance
Part–4 Effective Braking Techniques

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This page was last updated
Thursday, 27-Jan-2011

Effective Braking Techniques