Martin is quite right Trivelox are famous for the sliding sprocket
derailleur which maintains the chain line. They made three models of
gears and I think these were designated "A" "B" and "C" type. One was
the sliding sprocket another the straight forward conventional
derailleur and the last was this normal derailleur with a free wheel hub
unit. Racing tandemist's loved the last as it took no end of welly! All
three of these were available in the late 30's. Did Triumph make
Trivelox gears?
Mick Butler Hunts. UK.
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Michael Francis Butler
michaelbutler@fastmail.fm