Fading of Brake Pads

Fading of brake pads occurs for several reasons. All friction material has a coefficient of friction curve over temperature. Friction materials have an optimal working temperature where the coefficient of friction is the highest. Sometimes you can use the brakes so hard that you get the temperature over the point of maximum friction to where the coefficient of friction curve starts to decline.

The mechanics of this decline in the coefficient of friction are varied. At a certain temperature, certain elements of the brake pads can melt or smear causing a lubrication effect.  This is the classic glazed pad. Usually the organic binder resin starts to go first, then even the metallic elements of the friction material can start to melt. At really high temperatures, the friction material or the brake pads starts to vaporize and the pads can sort of hydroplane on a boundary layer of vaporized metal and friction material which acts like a lubricant. Fading of brake pads is felt as a vehicle that still has a decent, non mushy feeling brake control that won’t stop even if you are applying as much pressure as you can. Usually it builds somewhat slowly giving you time to compensate for it ,but some friction materials have a sudden drop off of friction when the heat is put on them resulting in sudden dangerous fade.

Reducing Fading of Brake Pads 

Fading of brake pads is fixed by using pads with a higher coefficient of friction at higher temperatures. 

Brake pads can be roughly broken down into about four types:

1. Organic - Made of materials like cellulose, which are like ground up cardboard. The cellulose is held together with a phenolic resin binder which is a heat resistant thermosetting resin. Pot handles and items like that are made of phenolics. Organic pads used to have asbestos to give better high temp properties but since asbestos is now a carcinogenic no-no, kevlar, fiberglass and mineral fillers are now also used. Organic pads have a good coefficient of friction for a light control effort, work well at low temperatures and are very quiet. Organic Brake Pads do not work so well for high performance use as they quickly wear, fade, oxidize and crumble. Organic pads are kind of old school and are common on cheap aftermarket replacement pads for older and sometimes new cars. These pads do not wear the rotors very much. Some vehicles have these as stock pads. Beware of these as they are worse than the stock pads. Suspect any cheap aftermarket pad. Organic pads are usually a light brown or tan in color.
2. Semi-Metallic - These have some powdered metal added to the organic mix to help stabilize the coefficient of friction at higher temperatures. Typically powdered brass, iron or Bronze is added. Chopped brass or bronze wire is sometimes added to help give the brake pads more mechanical strength. Most stock brake pads on newer vehicles are semi-metallic. Usually these pads are excellent for all-around use. They can run the gamut from very little metal to almost all metal. More metal usually means better high temp properties, more noise, more rotor wear and less effective cold braking. Semi-Metallics run the gamut from light tan with metal flecks in them to a dark gray in color. The darker pads usually indicate a higher metal content.
3. Full metallic - These pads are made of sintered metal with very little binder. Sintered metal is powdered metal that is pressed into a mold at high temperatures until it becomes a more or less homogeneous piece. Pads of this type are pretty aggressive with ones made of brass, bronze or copper or a mix of metals being more streetable and ones using iron being more high temperature oriented. For very high temperature use, ceramic powder is added to the material of the brake pads. Full metal pads are noisy, don’t grip when cold or wet and chew up rotors with annoying regularity. 
4. Carbon - Carbon pads available to us mere mortals are not the amorphous carbon-carbon exotica that F-1 cars, the space shuttle and high performance jets use. They are not "carbon-fiber" either. Carbon pads that are available to us normal people are semi-metallic pads that have powdered carbon added to them to improve their high temperature properties. For the most part, they have the cold friction of a good mild semi-metallic with the high temp properties of medium aggressive full metallic. Even the full race, high metal/carbon pads seem to have a fairly wide effective heat range. They for the most part are fairly good on the rotors also. Since they work so well over a broad range, carbon brake pads seem to have taken over the high-performance street car pad market. The only drawback that these pads have is cost. They are pretty pricey.  Carbon pads are a flat dark gray to black with a flinty look.

Brake Pad Recommendations

In short, to avoid pad fade, select a pad whose operating temperature matches the type of riding you do. If you ride mostly on the street, be realistic and select a pad whose operating temperature matches street conditions, as a pad with poor cold characteristics can actually be dangerous. You can change to a more aggressive pad for weekend action in less than half an hour so don’t give yourself brake pads with poor cold stopping for everyday use!