John E

Not true. On each road bike I have 11 non-redundant ratios, excluding large-large crosschain, with an average 7% progression except at the very bottom and sometimes (1.5-step) at the top. Most of the 2x9 or 2x10 systems suffer from redundancy where the two low and high ranges overlap. Since I choose not to waste space on any gears over 100 gear-inches or on redundancies, I can concentrate my (optimally close) ratios right where I need them. If I have a well-engineered half-step with a 2-tooth progression in back, such as Capo #2's 49-46 / 14-16-18-21-24-26, or the Peugeot's 45-42 / 13-15-17-20-23-26, I get about the same ratiometric spacing as someone with a single tooth progression corncob.

I sometimes feel that my Bianchi's 1.5-step 50-42 / 14-16-18-20-23-26 could use a 90-inch gear, which I could provide with a 7-speed freewheel, viz: 50-42 / 14-15-16-18-20-23-26.

Since there is little point to having two gears less than about 5 or 6% apart, 10 steps (11 unique ratios) of 7% can easily cover the 2:1 range from the mid-90s to the upper 40s. Allow a gap at the top and the bottom, and you have covered 96 gear inches down to 44 with two chainrings and six cogs.