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Formula for actual # of usable gears
I have 21 "advertized" gears (3-front, 7-reqar). With my seventeen inch
chain stays that reduce chainflex, combined with the half step granny configuration I have 17 useable and different, evenly spaced gear ratios (18, if you count the one redundant ratio shared by the granny and middle rings). How do you figure that into your theory? - - Compliments of: "Your Friendly Neighborhood Wheelman" If you want to E-mail me use: ChrisZCorner "at" webtv "dot" net My website: http://geocities.com/czcorner |
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#12
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Formula for actual # of usable gears
Mike A Schwab wrote:
... And in actuality, I like to figure, for my Sun Bicycles EZ-1 with a triple chainring and 3*7 SRAM rear wheel, that I don't actually have 63 gears. I start by considering the internal hub and chainring are in the middle. I can change the cassette up and down over 7 gears, about 10% difference each. If I hit the limits, I can change the chain ring, for a 20% change or 2 gears on the cassette. If I am at top speed, using the hub overdrive adds more resistance and ends up slowing me down. If I am climbing, I can use the underdrive for about a 25% drop in effort, about 2 more gears. If I rush to stop without downshift, I will use the under drive to get started and downshift the derailers and go back to hub direct drive. So even though I have a hugh number of gears, the hub just gives me a 25% lower range in gear ratios. I think a more accurate calculation would be to count the # of cogs (7), + 4 additional gears for the two additional chainrings, + 2 for the hub underdrive. With 52/42/30T chain wheels, an 11-28T 7-speed cassette and a SRAM Spectro 3x7 hub on a RANS Tailwind, I have about [1] 22 distinct ratios and 41 practical duplicates. However, the 3x7 hub adds 4 very useful ratios, extending both the high and low end gearing. [1] About, since it is a judgment call on how close the ratios have to be to be considered functional duplicates. -- Tom Sherman - Holstein-Friesland Bovinia The weather is here, wish you were beautiful |
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