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Ask the Expert on Bike Acceleration
continued from American Bicyclist
by John Allen
Acceleration from a stop uses a sequence from about 35 to 75 gear inches (3 to 6 meters development). Preferably, set up your bike to make this sequence easy-shifting. You shouldn't have to fish around for the bottom gear of the acceleration sequence.
An internally-geared hub is best for acceleration, because it shifts when the bicycle is stopped or moving very slowly, and you can easily tell what gear the hub is in. Hubs with 5 or fewer speeds should be set up so the starting gear is their lowest gear. If a hub has more than 5 speeds, the starting gear might be second gear or higher, with lower gears for steep climbs. Unless all the roads in your area go downhill in both directions, or you ride in pacelines, low gears for climbing are more important than having a top gear above 85 inches (7 meters), but if you can have a higher gear without sacrificing the low gears you need, go for it. Often, internally-geared bicycles are overgeared, and so it may be to your advantage to install a larger rear sprocket or smaller chainring.
Derailleur gearing works best for acceleration by shifting through the acceleration sequence using only the rear derailleur. If the starting gear is on the largest, inner sprocket at the rear wheel, you find the starting gear simply by shifting the rear derailleur to the end of its travel – entirely by feel. Relatively wide ratios in the low gears (larger sprockets) work best, so you don't have to shift every couple of pedal strokes at low speeds.
There are a few cassettes that work especially well for acceleration. One is the 7-speed Shimano M cassette, 13-15-17-19-21-24-28. This sequence also is available with the SunRace FW763 freewheel.
The custom CS836 8-speed from Harris Cyclery, http://www.sheldonbrown.com/harris/k7.html, also is good: 11-13-15-17-19-21-26-32, but I'd prefer 11-13-15-17-19-22-26-32 or 13-15-17-19-21-24-28-34 for a smoother increase in the size of steps toward the larger sprockets. There's a lot of freedom of choice of Shimano freehub cogs, at the expense of slightly worse shifting.
The Shimano CS913 and CS914 9-speed cassettes both have the same reasonably good sequence: 12-13-14-15-17-19-21-24-27, but I'd prefer a 9-speed like: 11-12-13-15-17-19-22-26-32 or 11-13-15-17-19-21-23-26-32 or 11-13-15-17-19-21-24-28-34 or 12-13-15-17-19-21-23-26-32 or 12-13-15-17-19-21-24-28-34 for wider ratios at the bottom end -- and these might be assembled as a custom job.
Most of the stock 9-speed combinations have a big jump in the middle of the range, in spite of the large number of cogs, or don't have a large enough inner cog. I bemoan the demise of half-step gearing, which component manufacturers no longer support. This system can give you close or wide ratios, depending on how you shift, and a wide range with only 5 or 6 sprockets.