I am confused by this advert. As I understand it the TriVelox C-1 was a conventional pull-chain derailleur that moved the chain sideways over a relatively conventional three speed freewheel. This is not the device shown in the picture.

The TriVelox A-1 was a radical design with a static derailleur-like chain tensioner and a three speed freewheel that was moved side ways by a cable pulling a toggle chain. This is what is shown in the picture.

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• Publisher: The Bicycle
• Country: UK
• Date: October 1948
• Derailleur brands: TriVelox
• Derailleurs: TriVelox A-1?, TriVelox C-1