The brakes on your car will be perhaps something you take very much for granted. After all, when you recognise the need to lose speed you just lift off the gas, put your foot onto the brake pedal and the car slows down. Nothing to it is there, but how and why do your brakes slow or stop you? What's going on underneath you. Let's have a look through this set of three articles to see what it is all about.
When you apply you brakes you will only be able to slow at a rate according to the amount of grip your tyres have on the road, and tyres get their grip on the road from something that is called downforce. Downforce is present within a road car due to the mass of that vehicle acting downwards onto the road surface, this being caused by the force of gravity. Therefore, if you have a car that weighs 1,000kgs, and that weight is evenly distributed within that vehicle, you will have 250kgs of downforce at each of the four wheels to create friction between rubber and tarmac.
When you apply your foot brake, and the car tries to lift its rear end off the road, it does not lose any of its 1,000kgs in total weight, as whatever comes off the rear axle has to go somewhere, and that somewhere will be the front of the vehicle. This is why cars and other road vehicles are fitted with bigger and more powerful brakes at the front, as compared to those at the rear. Under braking the front tyres will give you better road 
adhesion as opposed to those at the rear, so it makes sense to create the most braking force where there is the most grip. With less downforce between tyres and tarmac at the rear, any substantial braking going on at this end of the vehicle would easily result in a wheel lock-up situation. Braking systems on road vehicles have pressure limiting valves built into them that detect the difference in downforce between the front and rear of the car and will adjust the amount of braking effect that occurs over the length of the car so as to prevent rear wheel lock-up.Braking is perhaps something that nearly every motorist takes for granted. You are drive along the road and you come across a situation that requires you to lose speed. Without further ado you put your foot on the pedal and you slow down, but the question is how do you brake, by what degree and when? What is it that actually slows or stops the car?
There will be many people that have travelled as a passenger in car, perhaps driven by a friend, spouse or a relative, and wished they had remembered to travel with their surgical collars fitted so as to help prevent the jarring of their neck. You know the type of driver? The one that 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 what should have been a gentle process of slowing now becomes an eye-popping and rather hurried stop. Apart from being very uncomfortable, and there being an enhanced risk of skidding or control loss, it is quite harmful for the car. Think about the stress it 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 as your shopping jumps forward off the rear seat. There is a lot of stress going on here.
For the highest degree of control, braking should be completed when travelling in a straight line and always be carried out progressively. Remember what we have said about loading wheels and tyres in matched pairs? Upon realising the need to stop, firstly rest your foot on the pedal and then gradually increase the pressure until the desired amount of braking effect is achieved at the wheels. 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. In fact, braking should be pooh-shaped, that is to say it should be tapered at both ends and fat in the middle, and it is amazing how by pondering upon that thought your braking technique suddenly becomes much smoother. It also should be commenced early to give time for it to be delivered smoothly and progressively, so as to provide the maximum degree of vehicle control.
Braking whilst cornering will immediately put the car off-balance, as under the effect of deceleration the front of the vehicle is more heavily loaded, and because you are steering, that extra loading becomes unbalanced by acting on one front corner. This places a hell of a load onto that one suspension unit and creates a great deal of extra work for one tyre to have to cope with. When this happens, particularly with front wheel drive vehicles, the rear of the car becomes lighter, and with the dramatic unloading of the diagonally opposite wheel and 
suspension unit to that which has been unnaturally and unfairly burdened. This makes it more difficult for the back tyres to grip the road, due to the reduced amount of downforce, and the back of the car can more easily become provoked into overtaking the front. Applying the brakes whilst cornering can even cause the rear tyre, the one travelling on the inside of the bend, to lose contact with the road altogether, as vividly illustrated in this photograph.
The other product of braking into a bend is that the car will want to push straight ahead, instead of changing direction as you had intended it to, and so understeer can be induced.
The usual way in which the general motoring public deal with bends and corners is to decelerate, brake and change down through the gearbox all whilst steering around a bend, with all these actions usually being completed at the same time. In fact, most will only reach the most appropriate road-speed for the bend, and have selected the appropriate gear, at the point when they are at the halfway-round point. The effect of this is very uncomfortable for the car, because as soon as the foot is lifted from the gas, and/or the brakes are applied, the balance of the car changes so that the emphasis on downforce is biased towards the front, and if steering is applied as well this will create a greater potentiaal for things to go wrong. Not only that, but it knocks the hell out of your tyres too. Drivers who brake into corners will scrub the outer shoulders of their front tyres away and won’t get anywhere near the mileage they could out of them. They also accelerate the amount of wear and tear that occurs within the suspension componants.
The method we advocate in relation to braking for corners is to firstly bring down the speed of the car until we are happy that it is appropriate for the corner or bend we are about to enter, and whilst still travelling in a straight line. Having settled the car to the speed required we now directly select the most suitable gear that will give us the necessary response relative to the speed at which we are travelling - again before we start to turn into the corner. By the time we do turn into the corner we are travelling at the right speed and with the right gear engaged (we won't go into the positioning here as that would over-complicate matters for now). When we actually take the car around a corner/bend we are doing so under enough throttle applied to keep the engine pulling, but without the car accelerating, thus achieving the best-balance situation in terms of vehicle stability.
Going back to the subject of front wheel drive briefly, I remember a track day I attended once as guest, and where I met a young man, who among all the Lotus, TVR, Marcus, Ferrari, Audi and other motoring exotica, was there with his Peugeot 306 1.6. I do not like crossing talk of track driving with that of road driving, because the techniques and the method of how you drive the car for each environment are totally different and should never be confused with one another. However, in this circumstance there is some relevance in part to the story.
As stated, at this event there was the usual motorised exotica, most of which I had a ride in and most I drove over the course of the day so as to perform a demonstration lap or two to the owner. I met my new friend as he was examining the front tyres of his car whilst in the paddock, and as I walked by him I enquired if there was a problem. He lamented to me that the tyres were brand new and that he had taken the outer shoulders off them - mostly from the off-side tyre. I had seen this car throughout the morning many times, but always spinning in circles or sliding across the grass with turf flying up all around it. Declining my next ride in something a good deal more powerful I jumped into the passenger seat of the Peugeot. All around the circuit I was shouting at this young man - shouting until I was hoarse, giving instructions until he finally got the technique. His excitement when we overtook an Audi TT between two corners was amazing, but together we achieved it and it was all down to technique, because the Peugeot certainly did not have the power to match the Audi.
The point of mentioning this was that prior to making this good progress, my driver was lifting off power after he had applied the steering for the corners. The second he did this the car when into a violent spin, even though the track was bone dry. Lifting off the power in a FWD is like applying brakes only to the front wheels, this braking effect being due to the retardation effect of the engine. When you drive in this way the back wheels, which are now being slowed only by the car they are fixed to, want to overtake the front, as they are beginning to act like the bag of groceries you left on your back seat that will slide forward onto the floor under braking. The reason for this is due to what was said at the beginning, in that the rear tyres under braking, or even deceleration, will lose a significant amount of downforce, and therefore their grip on the road. The steering input at this point has the effect of shifting that distribution of downforce, that is taking place on the front, away from centre, and the counter action going on at the back end induces the spin with the car pivoting about the most heavily loaded front wheel. Under harsh track driving conditions it didn't matter that the surface was dry, as the sudden, almost violent, shift in loading was enough to send the car off the road in a spin. Once my driver kept the car balanced properly by braking before the bend and then applying gentle power through the curves, the car flew around the track and was a lot easier to keep under control.
You don’t get away with it in a rear wheel drive either. If you think about what is happening under you when you drive you will understand what this is all about. When we accelerate the engine is driving the driven wheels. When we decelerate the driven wheels are now driving the engine, unless we depress the clutch, in which case the drive chain between the engine and driven wheels is broken, whereupon the engine will die to idle speed (tick over). To put it another way, when you lift off the power the fuel supply is stopped from reaching the engine, but he engine doesn’t stop running. It keeps going, because now the momentum of the car pushing along the road keeps the engine running at a rate that is consistent with the road speed of the car. This is producing a braking effect at the back wheels, and if we have a car that has a very torquey engine, the torque that gives us so much driving power, now acts in reverse when decelerating, or on over-run as it is called. Lift your foot off the gas sharply, or if you select a low gear and then are rough with the clutch, you might just as well pull the handbrake on, because that is the effect you are having on the car. This is how so many TVR driver's end up in a spin, and more so than when the driver applies too much power in a corner.
When not causing you to spin, braking in corners not only scrubs the edges off the front tyres and gives an uncomfortable ride, but it leaves nothing in reserve for you to use if things turn more ugly.
Going back to that Peugeot 306 on that track day, out of all the cars I went out in during that event, that was the one that I enjoyed the most - not because I don’t like fast cars, but because I managed to make such a huge difference to one young man's ability to understand his car.
