Mechanical Knowledge@mechanical_4u
Before modern indexed shifting became standard, some bicycles used fully mechanical automatic derailleur systems that changed gears without any rider input. Designs like the Suntour Auto Shift relied on centrifugal force generated by rear wheel rotation to control when and how the drivetrain shifted.
As speed increased, internal rotating weights inside the mechanism moved outward, activating linkages that adjusted cable tension. This movement guided the derailleur across the cassette, allowing the bike to shift into higher gears automatically, then return to lower gears as speed dropped.
Although innovative, these systems were sensitive to setup and riding conditions, which limited their long term adoption. Advances in indexed shifters and rider demand for precise manual control eventually replaced automatic mechanical solutions, turning designs like this into a rare but fascinating chapter in cycling engineering history.
Video Credit: rbcbikes
