| 摘要 |
A two speed rear wheel hub transmission for BMX bicycles and the like that can be utilized as original equipment or as a conversion kit. High and low speed drive sprockets are mounted with intermediary overrunning clutches on the rear wheel hub of a BMX bicycle with each adapted to be concurrently chain driven by larger diameter high and low speed sprockets commonly mounted on the pedal drive shaft. Both the high and low speed drive systems are normally biased into driving engagement with the rear wheel hub but with the high speed drive system normally overriding the low speed system which free wheels during normal high speed bicycle operation. Downshifting is effected by a manually induced counter-rotational precessing of the rear wheel mounted high speed drive sprocket for selective driving disengagement thereof and automatic, delay free shifting to the low speed drive without effective interruption of drive pedal sprocket rotation.
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