The biggest issue every brake pad type has to overcome is heat dissipation. The friction of braking largely converts your kinetic energy (speed) into thermal energy (heat). Standing wave oscillations within the pad (brake squeal) is actually also dissipating a tiny bit of sound energy. Any pad that cannot effectively dissipate the heat it generates will not perform well for very long before it starts to degrade.

There are numerous cases where excessive rim pad heat has caused delamination of carbon clincher rims leading to catastrophic rim failure, often at high speed. In other cases tires have been blown off the rim and steel disc rotors have warped, causing massive vibration and loss of stopping power.

The maximum temperatures generated at the pad/rim surface during a long, steep descent at high speed can easily exceed 200°C / 392°F (also depending on the rim material). This potential maximum heat load significantly exceeds what is known as the glass transition temperature or Tg of most epoxy carbon rims leading to thermally induced mechanical failure.

As of writing only one or two major composite rim manufacturers can effectively handle such high heat loads using proprietary Resin formulations which resist thermal damage.

A pad specifically designed for composite rims will work effectively on an alloy rim, but since the compound is generally designed for higher temperatures, the braking will not be optimal. However, a pad designed for alloy rims when used on carbon will wear faster and deposit pad material on the rim as the pad disintegrates in the higher heat-load environment. Composites are very poor thermal conductors whereas alloy rims are very efficient thermal conductors.

That’s also the main disadvantage with ceramic as a brake pad material – Despite the exotic sounding name it doesn’t dissipate heat well (Ceramic tiles on the space shuttle heat shield); causing the other components on your bike’s braking system to potentially exceed their thermal design limits.