Quick release

A quick release skewer is a mechanism for attaching a wheel to a bicycle. It consists of a rod threaded on one end and with a lever operated cam assembly on the other. The rod is inserted into the hollow axle of the wheel, a special nut is threaded on, and the lever is closed to tighten the cam and secure the wheel to the fork. Wheels equipped with quick release mechanisms can be removed from the bicycle frame and replaced without using tools by opening and closing the cam lever, thus more quickly than wheels with solid axles and nuts. On the negative side, a quick-release hub renders a wheel more vulnerable to theft and care must be taken to ensure that the mechanism is properly tightened.

Similar quick-release mechanisms are also used to operate seatpost clamps, and the collapsing stem of folding bicycles and kick scooters.

The mechanism was invented in 1927 by Tullio Campagnolo, an Italian bicycle racer. He was frustrated when he attempted to change gears during a race. At the time there was but one cog on each side of the rear hub, so gear changes necessitated stopping, removing the rear wheel, rotating it horizontally so that the opposite cog is engaged by the chain, and finally reinstalling the wheel. The weather had turned cold, and his hands were numb, so he could not operate the wingnuts which retained the wheel. He had been well-placed prior to the gear change, but lost valuable time. This prompted him to develop the quick release.

Another Campagnolo invention that made use of the quick-release mechanism was the Cambio Corsa, a multi-gear changing system consisting of a rear wheel quick-release lever with a mechanical extension that placed the lever itself near the bicycle's saddle, combined with a fork that served as a primitive version of a rear derailleur (without idler pulleys to take up slack), that also had a control lever near the bicycle saddle. This innovation enabled bicycle riders quickly to change gears while in motion by releasing the axle, moving the rear wheel slightly forward by applying tension to the chain, actuating the fork to change to a larger sprocket, and tightening the quick release again; or else releasing the axle, actuating the fork to change to a smaller sprocket, moving the wheel slightly rearward by braking, and tightening the quick release again. The quick-release mechanism, along with other innovations and high standards of manufacture, enabled Campagnolo to become a leading road cycling and track cycling component manufacturer.

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Wikipedia