Most brakes are operated by pulling a steel cable, but hydraulic brakes work more like that of a car, using pistons to compress oil which then transmits the force. Hydraulics have lower maintenance than cables as they are sealed – cables can get gummed up with mud or rust. They are also very powerful, as they multiply the force of your hand. They are typically more efficient than cable operated brakes because there is considerably less friction in the closed hydraulic system between the lever and caliper compared to a cable operated system. Hydraulics are available to operate on the rim (like cantilevers) or as disc brakes. Hydraulics are more expensive than cable-operated brakes, and require expert treatment if they go wrong.