Updating drivetrain on a mountain bike
Updating drivetrain on a mountain bike - play fighting dating
An indexed shifter has a detent or ratchet mechanism which stops the gear lever, and hence the cable and the derailleur, after moving a specific distance with each press or pull.
In 1964, Suntour invented the slant-parallelogram rear derailleur, which let the jockey pulley maintain a more constant distance from the different sized sprockets, resulting in easier shifting.When a rider operates the lever while pedalling, the change in cable tension moves the chain-guide from side to side, "derailing" the chain onto different sprockets.For more information about the choice of particular gear ratios and sprocket sizes, see Bicycle gearing.The other end of the arm mounts to a pivot point attached to the bicycle frame.The arm pivots about this point to maintain the cage at a nearly constant distance from the different sized sprockets.In this condition, spring pressure takes care of the easier change to smaller sprockets.
In road racing the swiftest gear changes are required on the sprints to the finish line, hence high-normal types, which allow a quick change to a higher gear, remain the preference.In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain.Sometimes the rear-derailleurs are re-purposed as chain tensioners for single-speed bicycles that cannot adjust chain tension by a different method.Once the patents expired, other manufacturers adopted this design, at least for their better models, and the "slant parallelogram" remains the current rear derailleur pattern.Before the 1990s many manufacturers made derailleurs, including Simplex, Huret, Galli, Mavic, Gipiemme, Zeus, Suntour, and Shimano.The cage is positioned under the desired sprocket by an arm that can swing back and forth under the sprockets.