Four gears - two pedaling forwards and two pedaling backwards. It's hard to spin very fast backwards, so I made the low gears backwards and the high gears forwards. One quirk of the design is that the bike cannot be rolled backwards.
| Sprockets: | 16T (forwards) | 18T (backwards) |
|---|---|---|
| 52T | 88" | 78" |
| 40T | 68" | 60" |
Close up of chain idler. Idler arm and braze-on were made from sheet steel. SunTour ball bearing derailleur pulley.
The two independent single sprocket BMX freewheels. The first freewheel is screwed onto the rear hub, then an adjustable bottom bracket cup screws into the first freewheel and extends the threads so the second freewheel can be installed. Sturmy Archer 3-speed sprocket spacers are used as needed to make things fit. | 
Ancient Simplex front derailleur - probably from around 1960. One moving part that pivots on a mount brazed to the frame. No cable, just reach down and push the lever at the top. There is a set screw below the pivot point to limit travel inward. The tape above the pivot holds a spacer to limit travel outward. |
Springs for the idler arm are visible under the bottom bracket. They are secured to the old front derailleur cable braze-on with safety wire.
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frankb@frankb.us
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