They employ a single fixed rear gear, or cog, that does not freewheel. A Hyperglide freewheel or cassette on a bike with friction shifters can further improve shifting. The stator was equipped with a sprag clutch enabling it to freewheel when required. Some cars have a freewheel that disengages the driveshaft from the driven shaft. This variant also allows stoker and captain cranks to freewheel (coast) independently. One of their models featured the unusual Shimano front freewheel system. The special built bike has a single freewheel and no brakes. Unicycles usually, but not always, lack brakes, gears, and the ability to freewheel. This locks or unlocks the main shaft with the freewheel hub. Another is to use a hub designed for use with a threaded multi-speed freewheel. The gearbox and traditional Rover freewheel were kept unchanged from the previous model. Unlike a handcycle, a wheelchair with Freewheel continues to be propelled via the rear wheels. In the late 1890s came the introduction of rim brakes and the freewheel. This device locks the freewheel mechanism when in reverse gear. A double freewheel, preferably using no-backlash roller clutches, is considered superior.