Brake discs for a critical part of a modern cars braking system. There job is to dissipate the heat created in the process of transforming the kinetic energy of the car into heat energy.
Brake drums came before brake discs but they are limited with regards to how much heat they can deal with which is why modern cars use disc brakes.
As mentioned in other brake information articles, the job of the braking system is to transform kinetic energy into heat energy.
Disc brake carry out this process by rubbing a brake pad against a brake disc.
This action creates massive amounts of heat and it is the job of the brake discs to transfer this heat away from the braking surface and into the air.
Depending on the vehicle this can be done with various designs. The most straight forward is a solid disc. This transfers heat into the air from each face of the brake disc. This type of discs is usually found on lower powered cars or on the rear of normal cars. The solid brake disc is the most basic form of brake discs and has the lowest capacity to transfer heat into the atmosphere.
The next step after solid brake discs is vented brake discs. Vented brake discs have large spaces between the sides of the brake discs which is occupied by fins. As the brake disc turns the air is forced to the outside of the disc through the vent between the discs surfaces. New cooler air is then drawn into the centre of the disc which then passes to the outside of the discs and so on and so forth.
Vented brake discs are much more efficient that solid brake discs for 2 main reasons.
1. Vented brake discs have a much larger surface area than solid brake discs. Not only do vented brake discs have their braking surfaces exposed to the air but the gap between the braking surfaces are also exposed to the air as are the vents the fill the gap between the brake discs surfaces.
2. The effect of the brake discs turning is also used to draw fresh cool air into the centre of the disc and expelled at the outside of the disc.
Solid and vented brake discs can usually be found on standard cars. There are further steps that can be taken to make brake discs even more efficient
Drilled Brake Discs
Drilled brake discs were more popular in the 90s and 80s and their primary purpose was to save weight. However drilled brake discs have a fatal flaw in that they can crack. If you want to create stress fractures in something the best thing you can do is drill a hole in it.
Although drilled brake discs do save a bit of weight the downsides are great and you will very rarely see drilled brake discs on a racing car which should tell you all you need to know.
Grooved Brake Discs
Grooved brake discs are common in motorsport. Grooved brake surfaces have numerous benefits over plain faced discs as found on standard cars.
1. When brake get hot the brake pad can start to give of gas, this gas can come between the brake disc and brake pad reducing the co-efficvent of friction. The grooves in the brake discs can physcially wipe away this gas layer to keep the surface between brake pad and brake disc as clean as possible.
2. The grooves give the gases somewhere to escape.
3. Groove disc surfaces have a greater surface area than plain disc faces this helps cooling very slightly and the grooves also create air turbulence on the disc face helping to circulate the air.
The downside of grooved brake discs is that they can shorten the life of brake pads.
There are a number of variations of grooves. From the straight grooves found on Tarox performance brake discs to curved grooves with dimples on EBC Turbo Groove brake discs so fish-hook grooves as found on Alcon brake kits.
So in summary
The job of the brake discs is to dissipate the heat created by the braking process into the air
There are a number of different types of brake discs
Performance brake discs increase the heat dissipation properties over the standard brake discs
Performance brake discs when combined with performance brake pads can hugely increase the effectiveness of a car’s braking system