Brake Fade

!±8± Brake Fade

Some of the Physics

We know from our school days that energy cannot be created or destroyed - it changes form - Einstein

The kinetic energy of the car in motion is transferred by the brake system into heat energy when brakes are applied.

Kinetic energy E = ½mv2 (m = mass, v = velocity)

So if the weight of vehicle A is twice the weight of vehicle B in order to stop over the same distance and time, twice the amount of braking energy is required to stop the vehicle. If both vehicles had the same weight but the speed of vehicle B is twice that of vehicle A then four times the amount of braking energy is required.

Modern vehicles have disc brakes where the disc is rotating with the wheel and these are slowed down by clamping a friction material against them (Pads). The friction creates a tremendous amount of heat energy that directly relates to the weight and speed of the car. The brake system for a car is designed around creating enough friction to get the job done; by a combination of the radius at which the pads act to give leverage, the size of the calipers (the pistons give the necessary pressure), the size of the friction area (size of the pad) and the pad material. Therefore for a big heavy car that is capable of high speed you need big diameter discs to allow for a lot of leverage acting against the rotation of the wheel, you need big calipers to be able to apply a large amount of force to create friction between the pad and the disc and of course you need a large pad to give the biggest frictional area.

Regardless of the car size and braking system there has to be a way of removing the heat from the system so that it does not become overwhelmed this is usually an air flow passing through and around the system while the car is in motion.

The Problems

Under normal road conditions the time that elapses between braking is sufficient for the disc and pad cool down, however on a track with a lot of repeated hard braking the heat builds up. Two things that are undesirable can then happen, both are known as brake fade.

Pad Fade

Is where the heat pushes the pad beyond its working temperature that will cause it to start to disintegrate. The brake pedal remains firm but the vehicle does not slow effectively and speeds must be reduced.

Pedal Fade

Is where the heat transfers from the pads into the pistons in the calipers. The pistons (normally produced from aluminum) in turn transfer the heat to the brake fluid, when the brake fluid overheats it loses effectiveness and can even boil. When the fluid boils the gas created is compressible, so when the pedal is applied it softens and in extreme situations can "go to the floor" - when this starts to happen it is best to back off and let your brakes cool or they might be lost completely.

The Solutions

There are a number of solutions to avoid brake pad and pedal fade; some are more expensive than others.
· Upgraded pads (will not reduce Pedal Fade)
· Upgraded Brake fluid (will not reduce pad Fade)
· Vented discs - upgraded calipers and Pads (Expensive)
· Ducting air towards the disc and caliper (can be tricky to get right)
· Installing Titanium Brake Shims - TiBrake - between brake pad and caliper

(low cost easy to fit, will work for Pedal fade, but will not solve Pad fade)

Titanium Brake Shims - TiBrake

By inserting a thin shim of titanium (titanium has a lower thermal conductivity than other suitable materials), between the back of the brake pad and the caliper, the transfer of heat from the pad to the caliper and the fluid will be greatly reduced, so that you reduce the chance of brake fade and your brake system will last longer.
TiBrake titanium shims are cut using EDM (Electro Discharge machining) this ensures the accuracy of the cut but also unlike other cutting techniques creates no burrs, making the shims safe to handle and install. The shims are cut to suit the size and shape of the brake pad, so that the maximum barrier between the Pad and the brake fluid is achieved.

Why Titanium is the right material for a Brake shim

It provides the ideal mix between strength vs. weight, corrosion resistance and thermal conductivity
It is well known that Titanium alloys have excellent strength to weight characteristics. In fact Ti-6Al-4v (the most widely used alloy) has greater tensile strength than high strength Steel but is 42% lighter.
Titanium is inert and therefore corrosion resistant, it does not react to salt water, sunlight, or any body chemistry. This means that it is safe to handle and it won't corrode. It is used in the offshore oil and gas industries.

Titanium has a low coefficient of thermal conductivity and a high melting point +1600 Deg C, this enables it to perform as an effective thermal barrier in a brake system.

Material Coefficient of Thermal Conductivity

Titanium (Alloy Ti-6Al-4V) 7.5
Aluminium 130 - 220
Steel 30 - 50
Copper 300 - 400
Wood 0.04 - 0.4

This is why Pan handles are made of wood