Tag Archives: heat

Brakes – How They Work

Car brakes and brake in general work by changing kinetic energy into heat energy. Brakes do this by rubbing two surfaces together to create heat.

In the case of a modern car’s braking system these two surfaces are the brake discs and the brake pads. When the brake pedal is pushed the brake pads squeeze the spinning brake discs to create the heat and to slow the car down.

Performance brake parts increase the performance of a standard braking system by increasing the amount of energy that can be transferred in a shorter amount of time.

In a standard braking system the brake pads are usually the weakest link. Standard brake pads can be overcome by the heat being created which leads them to give off gas which gets between the brake discs and brake pads which massively reduces the friction available.

If you have ever felt this on the road you know what a “not good” situation this is. The symptoms of the brake pads overheating is a strong brake pedal, ie not soft, but no matter how hard you press the brakes you cannot lock the tyres and/or the car does not stop any quicker.

This problem of the brake pads overheating is called brake fade and is the biggest issue in standard braking systems.

To overcome this problem of the brake pads overheating performance brake pads can be fitted. Performance brake pads are designed to be able to cope with higher temperatures than the standard brake pads and have the side benefit of being able to last longer.

The downside of performance brake pads is that they tend to cost more than normal brake pads although you may get the money back through savings in garage costs because they could last 2-3 times longer than cheap replacement brake pads.

There is another type of brake fade and this is down to the brake fluid. Brake fluid absorbs water from the atmosphere and water has a lower boiling temperature than brake fluid. As brake fluid absorbs more and more water, its boiling point reduces.

The symptom of old brake fluid is a soft brake pedal under braking. The soft pedal comes from the brake fluid compressing. While water and brake fluid are not compressible, when brake fluid boils because of a high water content, the boiling introduces bubbles into the hydraulic system which are compressible.

If your brake pedal is close to the floor or if it is soft or if you need to push hard on the pedal to get meaningful retardation then your brake fluid may well need to be changed.

Brakes – Summary

Brake systems work by transforming kinetic energy into heat energy

The braking capacity of a brake system is limited to the amount of energy it can transform into heat

When the brake system is overcome with heat, brake fade occurs. This is usually down to the brake pads expelling gas or the brake fluid boiling

Upgrading brake pads to performance parts is a major improvement and regularly changing  brake fluid is also beneficial

For the ultimate increase in the heat capacity of your cars braking system a big brake kit is the answer.

 

Brake Fade Symptoms

First of all let’s recap on how brakes work, specifically disc brakes.

 

Disc brakes consist of brake pads and brake discs. The brake pads clamp onto the brake discs when the brake pedal is pushed. This creates friction between the brake pads and the brake discs which creates heats.

 

This heat is the key to how brake systems work; they convert kinetic energy to heat energy. The faster they can do this the faster your car will stop.

 

Brake fade happens when the heat created is too much for the brake pad to handle. All brake pads have a specific heat range in which they work well. If a brake pad is too hot or too cold they do not work properly.

 

Brake pad effectiveness is measured by its coefficient of friction. Companies like Ferodo will publish a graph for its brake pads which show how the coefficient of friction of the brake pad changes with temperature.

 

Brake fade happens when the brake pad becomes so hot it takes the brake pad outside its temperature window where it is most effective.

 

When brake pads overheat they emit gasses and can start to shed material onto the brake disc.

 

The symptoms of brake are pushing the brake pedal harder but the car does not stop any faster. In other words the stopping power loses connection with how hard you press the brake pedal.

 

Needless to say this is a very disconcerting feeling.

 

There is another type of brake fade. Whereas brake fade that is down to inappropriate brake pads the second type of brake fade is down to not properly maintaining the brake system

 

The second type of brake fade is related to the brake fluid in the system. Over time brake fluid absorbs water from the air and the more water it absorbs to more compressible it becomes. You can feel this compressibility as a soft/mushy brake pedal.

 

In the extreme, brake fade down to old brake fluid can lead to a driver push the brake pedal all the way to the floor with little increase in stopping power. Arguably, brake fade because of old brake fluid is more dangerous than brake fade due to low quality brake pads.

 

Fortunately there are things that can be done to a car’s braking system to massively improve the braking system to brake fade.

 

The most obvious step is to flush out the old brake fluid completely and refresh with the new brake fluid. This will give immediate benefits. First of all the brake pedal will fell much stronger, it will give much more resistance and the car will seem to stop with less effort.

 

The second step is to upgrade brake pads. The brake pads fitted to cars from the factory are designed to bring a car to a stop from high speed once, possibly twice in quick succession. After this brake fade usually starts to happen. This problem is quite easy to solve as there are many companies selling brake pads which are designed to work at higher temperatures than the original brake pads. These pads will be priced the same as what you get from a main dealer but they will far outperform the main dealer brake pads both for service life and in stopping power when hot. Brands like Ferodo and EBC make high performance brake pads for road use. Speak to your local performance car part dealer for advice on the pads which are best for you.

 

So in summary, brake fade is due to the braking system being asked to deal with more heat than it can handle. To raise the heat capacity of your car’s braking system new and/or uprated brake fluid should be used as well as performance orientated brake pads. Like most things, you get what you pay for, while there are cheap brake pads available their service life will not compare to performance brake pads costing 4 or 5 times as much.

 

With uprated brake pads and uprated/new brake fluid your car’s braking system will have a much higher heat capacity meaning you can drive your car harder before you start feeling brake fade.