Motorcycle Braking Systems
The three systems you're likely to come across
A braking system has one job - to turn speed into heat as quickly as possible.
Motorbikes have two usually independent braking systems - one on the front wheel and one on the rear wheel. The brakes on the front wheel are usually quite a lot more powerful than those on the rear wheel, because the front wheel has more traction under braking. The less powerful rear brakes are therefore more useful for making small adjustments to speed and making slow manoeuvring more precise.
Braking systems are defined into three different groups: Drum, Single Disc and Double Disc.
We start with the least capable braking system. Drum brakes have two pivoting shoes fixed to the frame, inside a casing which moves with the wheel. When the brakes are applied, the shoes move apart pushing against the casing. This causes friction, slowing you down.
Compared to the pads on disc brakes, the shoes of drum brakes have a larger surface area. This means that they don't get quite as hot because the heat is produced over more space.
Having all of the components enclosed has the negative effect that heat and moisture cannot be removed by air moving over the friction components. Any moisture that builds up on the friction surfaces acts as a lubricant until enough heat is built up to boil it off.
Single Disc brakes
Disc brakes are much simpler than drum brakes in that they're a just disc, usually made of steel, that gets squeezed between two brake pads. The disc is usually bolted to the wheel rim too, so you can actually see what's happening when you apply the brakes.
Compared to discs, brake pads are much smaller but can be forced into the disc harder than a shoe can be pressed against a casing, making for a more powerful braking force but a lot of heat in a small area. This leads to faster wear of the brake pad, which must be replaced much more often than drum brake shoes. Brake fade also hampers disc brake systems, but only when they're in near constant use such as when on a race track, due to heat being removed by cool air making direct contact with the friction surfaces.
Double Disc brakes
Exactly the same as the Single Disc except there are two of them! Double discs are either crucial or silly depending on who you ask. In theory, having exactly twice the friction means twice the stopping power, right?
Well, if you can already lock up a wheel with your single disc brake on a clean dry road having an extra disc isn't going to do much for you, as the weakest link is how much friction your tyres have on the road.
At the very least they make the bike look a bit more symmetrical and you will be a bit less susceptible to brake fade, as the heat is generated over four brake pads rather than two.