BRAKE, BRAKE, BRAKE…!

Whereas suspension kits are popular because a lower car looks cool and performance exhausts make the car louder as well as more powerful, brakes are often the last thing on people's modding lists because its perceived that they don't do exciting things to a car. However, good brakes can enhance your driving experience considerably as well as provide safer braking. Safer braking is perhaps a side benefit with properly modded cars being able to stop way quicker and more securely from legal speeds than standard cars but better brakes also allow later braking into corners and will resist the dreaded brake fade when worked hard on twisty back roads.

HOW BRAKES WORK

Car brakes work by converting kinetic (movement) energy into heat energy. When the brakes are applied and the brake pads are pushed against the rotating brake discs the resulting friction between the pad and disc surfaces produces lots of heat with temperatures up to many hundreds of degrees. This heat is dissipated to the atmosphere, mostly by radiation, but also by convective heat transfer directly to the surrounding air.

TOO MUCH HEAT
If the brakes get too hot you will experience problems. The friction surface of the pads can bake, resulting in a smooth glaze which drastically reduces friction. Resins within the pads can also vapourise, resulting in a gas layer between pad and disc. This also reduces friction.

LESS HEAT
Most modern cars now have vented discs on the front which vastly improves convective cooling with air passing through the two halves of the disc drawing heat with it as it goes. On more powerful cars it is now also standard practice to have vented discs on the rear too. If you're being really serious the discs can have shaped cooling vanes between the two halves of the disc drawing air out from the centre to the outside like a fan. These vaned discs can be extremely expensive as they have a machined internal finish rather than the usual 'cast' finish i.e. as it comes out of the sand cast mould.

PERFORMANCE PADS
The simplest brake improvement is to fit performance pads. These have a higher friction coefficient than standard pads and can run up to much higher temperatures. If your discs are up to coping with these higher temperatures then you gain from the greater temperature difference between the discs and the surroundings because heat will then be transmitted at a greater rate and the car will then slow down quicker. We sell a large range of performance pads with lots of different compounds from good fast road pads up to pure race pads.

WHAT'S THE CATCH?
As always in engineering there's a catch. Very high specification pads don't always work well from cold and they can be too noisy for road use. Have you ever heard a rally car at the end of a stage? The brake squeal can be ear splitting. The majority of pads we sell do not fall into this category, working well from cold with no squeal, but some of the race compounds do. There are however some pads on the market, particularly Pagid, which are essentially race pads but will work well from cold and are not too noisy. These pads are made from expensive materials and you tend to pay up to 3 times more than for more 'normal' performance pads.

GROOVES, HOLES AND DIMPLES
It's always a good idea to fit performance discs along with performance pads. Performance discs come with a mixture of grooves, holes and dimples which deglaze and de-gas the brake pads when they get hot, thus keeping the friction level high. Holes also enhance cooling by increasing air flow through the discs as well as increasing the overall disc surface area for heat transfer. Black Diamond offer a full range of choice with drilled-only, grooved-only and drilled and grooved discs. EBC and some others have opted for blind drilled holes (or dimples) along with grooves. Other manufacturers such as Tarox and Red Dot specialise in grooved discs with their most expensive discs having 40 grooves. As well as deglazing the pads, the increase in surface area with so many grooves will also help cooling.

THE HOLE DEBATE
With the advent of ever more powerful cars quite a debate has emerged about drilled discs. Those against drilled discs will tell you that the drilled holes are the source of cracking under extreme heat and that the holes are totally unnecessary. Whilst it is true that heat stresses are maximised at sharp edges if discs are well enough made from high quality castings it is not an issue - look at high end performance Porsches and Mercedes - a number of models have discs with multiple drilled holes. Of the brands that we sell you will see that Black Diamond, Tarox and Red Dot drilled holes all have chamferred edges which reduces heat and mechanical stress. We have fitted Black Diamond Combis (drilled and grooved) discs to a number of our own cars and friends' cars and have always found a great improvement in braking with no problems whatsoever. The only disc warranties that we have seen from any brand of brakes have been as a result of sticking calipers producing massive heat because the pads are jammed against the discs or discs being used outwith their limits, e.g. cars running twice their normal power with drilled or grooved discs of standard size where they really should be running larger diameter discs.

ANOTHER HOT PROBLEM
There's another downside to brakes getting too hot - the brake fluid can boil. Once it boils and produces vapour in the system you can get to the point that your brake pedal reaches the floor and all you have done is compress the vapour with no action on the brake fluid. The answer is to use fluid with a higher DOT rating. Most vehicles have DOT 3 fluid whilst race cars have DOT 5. DOT 4 is a good compromise for the road. It is also well worth considering replacing the brake fluid each year - experiments have shown that brake fluid can absorb up to 2% water per year and this dramatically reduces the boiling point of the fluid.

SIZE MATTERS
We at MSW have certainly found greatly improved braking performance when fitting discs and pads from various of our suppliers. It should be noted though that these are standard size replacements and there's only so far you can go in terms of friction and brake cooling. If you are really serious about braking then you need to consider a big brake conversion. The larger the diameter of the discs the larger the braking torque will be. Its just like a lever - the same force at a greater distance from the centre produces more turning torque. Also, larger diameter discs can have a larger friction surface to increase pad-disc contact thus producing even higher braking torque for the same braking force.

SO DO MORE POTS
Entry level big brake kits come with 4-pot calipers i.e. 2 pistons pushing each pad either side of the disc. Depending on the vehicle there is then quite a choice of calipers with 6-, 8-, 10- and 12-pot calipers being available along with increasing disc size. The only limitation is the space within the wheel. Kit manufacturers give guidance on the size of wheels that you will need to fit their kits and some provide a template you can cut out to see if their kit will fit within your wheels. The benefit of ever increasing numbers of pistons is not a greater braking force - the piston sizes are matched to the existing master cylinder - but the possibility of a larger pad friction area and more evenly distributed braking force over the pads which keeps the pads more parallel to the discs giving excellent pedal feel. Of course, more pistons in a caliper increases the price but once discs go above a certain size they also become more expensive because they need to be 2-piece to keep unsprung weight down. 2-piece discs have an alloy centre hub bolted to the steel outer rotor. This inevitably means that big brake upgrades do come at a price. Entry level kits on lighter cars can be as low as £700 but budget for £2000+ on more powerful cars with large discs.