Cyclo - Perry Coaster
Posted: Friday 12th June 2020
AVT sent me these images which I have tried to stitch together, not very well, but I think you will get the idea. I spent some time puzzling as to what was the point of this device. Eventually I realised that the rear hub constituted a derailleur/back-pedal brake and this tension device allowed one to pedal backwards putting the required pressure on the brake to operate it. This of course straightens the lower chain run under tension. The resulting chain slack on the top run is taken up by the conversion. The description below says that the pivoting cage pivots on the lower part of the attachment but I cannot see how this ties up with the illustration where it pivots on the upper part.
There are images of two different versions of this device, one with twin-pulleys and one with a single-pulley. It should be noted that the instructions state – only use a 46t chainwheel. This is to give the correct chain line through the device.