Fixed or Floating Callipers?
There are many different types of callipers in use on motorcycles but they are all either fixed or floating. A fixed calliper is one where the calliper body is fixed and both the calliper pistons which oppose each other are pushed by the hydraulic system.
A floating calliper is one that floats on a sliding pin set up. Here one pad is merely fixed to the calliper with no hydraulic input and the opposite side is fixed to the hydraulic system. As the piston on the hydraulic side is pushed it both applies pressure to its own pad and the calliper body slides away from force and thereby pulls the opposite pad onto the disc from the fixed side. The sliding calliper set up is not as powerful as the fixed calliper but it does have the benefit of being very narrow. This is a particular benefit where space is restricted and these days you mainly see sliding callipers used on bikes with wire spoked wheels. In order to have sufficient strength in the wheel design, the spokes are spread as wide as possible at the hub and therefore space for the calliper is very much restricted. In such circumstances a floating calliper is usually the best solution.