Front freewheel

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The Shimano front freewheel design was an innovative bicycle drivetrain design of the 1970s. To improve the normal bicycle with a freewheel between the rear sprocket cluster and wheel hub, Shimano inserted a freewheel between the pedal cranks and the front chainrings that enabled the rider to shift gears while coasting. For safety reasons, however, the normal rear freewheel also had to be retained to stop the chain if clothing got tangled in it, which would otherwise lead to injuries of the leg by the drivetrain, crashing of the bicycle, or both. In addition, the marketing followed Shimano's then-current path of beginning with lower-cost implementations of the system using low tech and usually heavier materials. For one or both of these reasons, the resulting system was substantially heavier than the standard freewheel and, in any event , did not penetrate the market noticeably, although some Panasonic bicycles were briefly equipped with it. It is now often seen as a solution in search of a problem.

Front freewheels can currently be found on bikes used for bike trials riding. Putting the freewheel on the crank allows some weight to be taken off the rear hub, centering the weight of the bike a little more, making it easier to lift the back wheel as well as simplifying the rear hub, allowing the bearings to sit as far outboard as possible, reducing bending on the hub axle. Because bikes with this set up are almost always singlespeed none of the gear shifting issues that arose in geared systems are problems with this arrangement. The reason for the adoption of front freewheels is likely to be due to the availability of extremely strong screw-on BMX freewheels before the advent of specific components for trials bikes. In fitting the freewheel to the cranks rather than to the back hub a smaller chainring size was possible at the cranks with a gear ratio suitable for trials, increasing the ground clearance of the bike. BMX freewheels could also carry more torque and were cheaper than mountain bike designed systems at the time front freewheels were introduced.