Ed’s Weblog

…now my real blog

Freewheel gear

I would like to have a significantly lower gear on the freewheel side than the fixed side, but this is of course limited by chain length. If the freewheel gear is much larger (lower ratio) then you need more chain to wrap it. I.e. you need really long dropouts and a radical change in wheelbase.

The Rivendell Quickbeam achieves a significantly different ratio with two chainrings with an 8 tooth difference and 2in long track ends! They also do this without flipping the rear wheel using the same cog, presumably resulting in a non-perfect chain line as well as the changing wheelbase. You can also use the other side of the hub for a 4 gear setup.

I was thinking of something similar, with two chainrings but also two cogs, but with opposite tooth number differences on the chainrings and cogs. I.e a 4 tooth larger cog would mate with a 4 tooth smaller chainring, resulting in no change of required chain length. This would also have a different chainline on the fixed and free sides. For example, 42mm on the free side and 47mm on the fixed side (is the thread long enough to allow this?), allowing the larger chainring to occupy the outside position on the crank.

Anyway, this won’t be in the first iteration of the bike, which will just have a single chainring and similar ratios on the fixed and free sides.


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