We Love Brakes

[Burn! Motorsport 20]

Here at Burn! Motorsport, as the Distributor for DIXCEL in Europe we love brakes and the science that makes them work. When taking on the Distribution we spent a lot of time learning about how they work and how to best make your choice in pad and disc. 

 

Over the next few days I hope to post some useful information about what we have learnt from our guys in Japan. 

 

 

Firstly the Brake Pad

 

When you exceed the capability of the OEM brake pads it's best to replace for something that better suits your needs and applications. 

There is often a misconception that you need to go to a 'race compound' to improve the braking performance. This is not true and race products shouldn't be used on the road - they can be very damaging to the rotors when outside the correct operating temperatures, which causes excess ferrious dust, noise and premature failure of the rotors. 

Coefficient of friction is the measure of the ratio of the force of the friction between two surfaces and the force pressing them together. This matters because if you have too much then the brakes are very hard to control and if you have too little you won't be able to achieve enough braking performance to stop. It is important to find a pad that has suitable coefficient of friction whilst being able to maintain it at various temperatures, allowing it to reach its coefficient of friction as soon as you stamp on the pedal. 

Fade resistance is the next characteristic to consider. Brake fade occurs in high temperatures when resin material in the pad vaporises. This creates a film between the pad and rotor reducing coefficient of friction. In general an OEM pad will have a fade resistance of about 300-350 degrees Celsius. Performance pads obviously have a much higher fade resistance, but this can come with an issue. Many high performance pads will only stabilise when they exceed a certain temperature giving poor performance from cold.

 

 

When choosing pads another common misconception is wear. People tend to believe that when you use a performance pad it will are faster. This is neither true nor false. This is because pad wear rate is different at different temperatures. A performance pad will be more resistant to wear at higher temperatures and an OEM pad will be more resistant at lower temperatures. You need to chose the pad that suits your type of driving best. This chart below shows different pads wear rates under different temperatures 

 

 

 

Brake Rotors (discs)

 

Brake rotors are a little less complicated as the same rules of Coefficient of Friction that apply to the pads also apply to the rotors, but with rotors they don't really come in too many different compounds. With brake rotors it is about choosing the best rotor for your application. A basic OEM rotor will conform to certain tolerances, when an OEM rotor is exposed to more extreme forces the rotor may become unstable and a suffer warpage or cracking - This is caused by weaknesses in the Residual Stress.

 

Residual Stress is a structural weakness that occurs in the casting process of iron, the main material used in brake discs. During normal street-use, residual stress does not cause any problems with the discs. When the discs are used at race circuits at high temperature conditions for an extensive amount of time, the residual stresses within the disc can lead to thermal cracking and deformation. Residual stress is relieved by a heat treatment process to prevent thermal cracking and deformation from occurring.

 

Heat Treatment Process can be applied to any discs to relieve the Residual Stress from the casting process. We offer The DIXCEL heat treated discs to customers planning on using their car on the circuit. The advantage of the heat treated disc is increased durability.The heat treated discs have better protection against thermal cracking, juddering, and distortion. 

 

The DIXCEL heat treatment process takes place over a 24 hour period. Starting from room temperature the heat is stepped up very slowly until the optimum temperature has been reached and then held for a number of hours and finally the heat is reduced again very slowly.

 

 

The result is a far more stable disc for circuit use. The chart below shows a comparison of heat treated vs non heat treated. 

 

 

    non-heat treated disc heat treated disc Crack resistance When a one-make series Honda DC5 Integra is driven at 2min 10sec/lap on the Motegi race circuit Hairline cracks occur on the braking surface after 1 hour of use. Hairline cracks occur on the braking surface after 2 hours of use. When an street legal Honda DC5 Integra is driven at 2min 20sec/lap on Motegi race circuit Hairline cracks occur on the braking surface after 2 hours of use. Hairline cracks occur on the braking surface after 5 hours of use. Judder resistance When a one-make series Honda DC5 Integra is driven at 2min 10sec/lap on the Motegi race circuit Minor juddering (vibrations) occur after 1 hours of use. Minor juddering (vibrations) occur after 2 hours of use. When an street legal Honda DC5 Integra is driven at 2min 20sec/lap on Motegi race circuit Minor juddering (vibrations) occur after 2 hours of use. No juddering (vibrations) occur after 4 hours of use.
 

 

Cast Iron and Carbon are the two main Brake Disc Materials. The benefit of carbon is its excellent high thermal resistance and it is lightweight. But as it is very expensive it generally only gets used by race teams and in high value motorsport. DIXCEL have chosen their own cast iron mix which is higher is carbon content than your run of the mill OEM disc. They also offer a 20% Higher Carbon mix in their FCR FP/FS series of discs that have been heat treated. These are more expensive due to the high carbon content but they are much more durable on the circuit and resistant to cracks and warpage. The FCR FP/FS rotors were developed for endurance racing and under severe conditions. They have excelled and are now the favorite among many race series around the world.

 

 

Slot or not to Slot

 

That is the question! Generally more slots the higher operating friction level, but increases air noise and faster pad wear. 

 

 

 

 

It is another common misconception that to increase the performance of the brakes you must run slotted rotors. However we often recommend plain rotors to customers with the correctly selected pads to exceed their braking performance needs. Often much better value for money can be achieved using a plain rotor as it will not wear out the pads as quickly. 

 

If you run them then which direction to run your slots?

 

If you made it this far well done! We could have gone into much more detail. However i do tend to bore myself sometime so I dread to think what you guys must think of me! 

 

Any questions fire away! 

Anthony 

 

[rob275 1817]

some good information and should help some people out on here, I've learnt something