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Racers claim that better brakes make faster lap times, but how can something that slows you down make you faster?
Simple; the better the brakes the longer you can stay on the power before braking for the next corner.
Brakes are all about heat, and ditching as much of it as quickly as possible, they work by converting the cars speed energy into heat energy which is then taken swiftly away in the air streaming through them, in theory. But a big car at high speed has an awful lot of energy; for instance getting a Bugatti Veyron to do an emergency stop from high speed might put the equivalent of several thousand bhp through the brakes make the discs glow bright red.
There are two basic types of brake, drum brakes get their name from the drum of steel with curved shoes inside that are pushed outwards against the inside of the drum when the brake pedal is pushed. These can be found on the back axles of cheaper cars and are quite frankly a bit pants; the braking force is limited, the pistons are small and the pressure pushing the shoes out into the drum is similarly small. By comparison disc brakes can exert a much higher force onto the disc without risk of it failing. It uses a disc with a set of pads held in a calliper that are forced against both sides of the disc when the pedal is pressed, generating much more force. In both cases the disc or drum part is attached to the wheel hub so it rotates with the wheel and the pads or shoes are held stationary on the axle, or strut, or what ever dangly bits are attached to the suspension.
All brakes work by friction, pressing a pretty darn tough pad of friction material against the spinning metal, the harder the friction material is pressed against the metal the more friction is produced and the greater the braking force. New pads will need to be bedded in before any serious racing, the exact procedure varies for different materials so read the manufacturers instructions before driving the car. Race pads often only work when they have a bit of heat in, some are unsuitable for road use and should be avoided if you have to drive the racer to events, check with the manufacturer for recommendations. This also makes the warm up lap quite important, and when starting a race caution and early braking may be needed for the first few corners.
Brake systems use a special type of hydraulic oil to drive the pistons which push the friction material into the disc or drum. At the pedal end there is another piston in the master cylinder which is connected by hydraulic brake pipe to the slave cylinders at each wheel. In some cars the brake force is artificially increased by a servo directly connected between the brake pedal and the master cylinder, this uses vacuum from the intake manifold to move a large diaphragm when the brake pedal was pressed, as the pedal moved down small holes in the servo control section are progressively uncovered which applies more vacuum to the diaphragm which in turn applies a greater force to the master piston of up to four times the force at the pedal.
Some cars with Anti-lock Brake Systems (ABS) use a powerful electric pump to do this instead. The ABS system measures wheel speeds and if it detects that a wheel is slowing down faster than a safe limit then it knows that that wheel is about to start locking up, so it lets the brake pressure off the individual wheel by opening a solenoid valve in the ABS valve block, just for a tiny fraction of a second until the wheel frees up just enough to know it wont lock. You can feel this when it happens as a sort of buzzing or vibration under the brake pedal. ABS allows maximum braking force without the risk of skidding. But if you are going to fast then you are still going to crash no matter what the brakes do. Some people remove ABS systems for race cars but if the regulations allow then keep it, it will hold the brakes at peak braking efficiency and control each wheel individually which is something no driver could do, the system rarely weighs more then a couple of kilos so removing it will make nor real difference to the cars weight.
The fierce heat generated from heavy braking has to be dissipated into the air which is why race cars have ducts taking fresh air from the front of the car to the disc centre, the hot air then has to go somewhere and the design of the wheel should allow it to escape readily through widely spaced wheel spokes. To get more heat into the air some discs are vented with radial channels cast into the disc to draw air from the centre outwards, vented discs are more or less essential on a racer and if your car doesn't have them it may be possible to swap with the brakes from a higher specc'd model. Some performance discs also have small holes drilled through for even more ventilation but these can lead to cracks starting unless they are made very well with radius edges, usually better to avoid them. Groves on performance discs can help remove the tiny gas layer that build up between the pad and disc sometimes and increase pad bite, the down side is that they can increase pad wear when used aggressively, the groves should have a radius at the bottom of the cut, if they are cut squarely into the disc then the corners may start cracks..
The brake size needed on a car depends on its weight and how fast it is likely to go, more powerful cars can more readily get up to higher speeds they need bigger brakes. Bigger pistons and a larger diameter disc make better brakes. Also if the brakes are going to be used for long durations, such as when racing, there is less time between brake applications for them to cool down adequately, this is where vented disks can be a real benefit.
All that heat soaks through the system into the brake fluid and although it is engineered to work at these very high temperatures in extreme cases the temperature can get high enough for the oil to boil, this generates gasses which compress easily and make the brake pedal feel very soft. This is brake fade and in really bad cases the brake pedal can sink to the floor with very little braking force generated, pumping the pedal up and down a few times can sometimes help but basically if the brakes fade on a race track then the car generally crashes. And it's always a surprise when it happens because heat builds during the last application then soaks into the fluid whilst the car is hammering down the straight, so when the pedal is pressed again there is nothing, even though it worked fine last time!
Old brake fluid absorbs water which boils and fades much more easily which is why it must be changed every few years to stay safe. Silicon based fluid is different and doesn't absorb water but moisture still pools inside the system and needs flushing through every few years, it's also a bit more squashy than mineral fluid making it unsuitable for fast acting ABS.
The DOT number can cause some confusion. Many people think a higher number is 'better' but this isn't necessarily so. The number refers to a test schedule with many features such as shelf life, water absorption, compressibility, this also includes fade resistance both new and when it has aged a certain amount, but race fluids age quickly and so only pass older DOT tests. Some DOT tests are for specific types of fluid, for instance DOT5 is only for silicone fluids which have to be tested slightly differently as you cant force them to absorb water, but DOT5.1 is for ordinary fluids, so you have to be careful. Most good race fluids are DOT3.
Another problem that can burden budget race cars is sticking brakes. If using standard callipers this may be because of the outer dust seals burning up and jamming the pistons, this simple solution is to remove them but remember that dirt will now get on the exposed part of the piston and will have to be cleaned off when fitting new pads. This seal must not be confused with the main fluid seal.
Brakes are often overlooked and any wear only becomes apparent at the mot or in an emergency stop. The trouble is that they have a hard life and can disintegrate with the friction material splitting off the steel backing or wearing down to nothing unnoticed, and they usually seem to work fine right up to the point were they don't work at all and you crash. Maintenance and regular inspection is vital.

One of the other problems on race cars is the handbrake seizing up. Never apply the handbrake after a hot lap as it will warp. Some people remove the handbrake completely and use a hydraulic one instead, this is particularly popular with rally cars where the handbrake is used when turning. This is a relatively simple mod where the hydraulic line running to the back brakes has another master cylinder fitted, the line from the foot brake goes into the reservoir connection and the back brakes connected to the normal outlet from this secondary master. A custom leaver is used to operate the secondary master. In normal operation the pressure from the foot brake goes straight through the secondary master and works as normal, but when the hand brake lever is applied the piston in the secondary master moves forward, isolating the front brakes and applying pressure to only the back brakes.

F1 carbon brakes only work properly when red hot, not much use on a road car.
But upgrading to better pads can really perk up standard brakes.
Pads, race fluid and braided hoses.
Swapping to brakes from a more powerful model can be a cheap rout, these Jag XKR discs and callipers found on ebay are massive but went for less than £200.
But not as massive as these full-on race 6 pot GT3 brakes, but at over 12 grand for a full set its way out of reach for most.
All that heat has to go somewhere, race wheels keep the spokes away from the disc and let the air flow freely on this MK1 Astra rally car.
These Porsche 911 Turbo wheels take it a stage further and have angled spokes to work like a fan. But painting the callipers red does not make them more powerful!
Close up of a well used calliper with the pads removed, the pistons get a hard life and maintenance is essential. Note the outer dust seals which can jam up.
Drum brakes can be a bit rubbish but still fitted on the back axles of cheaper cars, the best mod is to fit discs of another model. They can be improved with vented drums and race shoes
Some rear discs have a tiny drum brake built into the centre just for the handbrake, often called 'drum in hat' as it sits in the hat shaped part of the disc.
          

©Ralph Hosier