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Old 03-29-19, 05:03 AM
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rhm
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Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...

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Originally Posted by Carbonfiberboy View Post
Stonich recently provided my stoker wife with 151mm tandem cranks. She loves the new cranks. Crank formulas say 148mm for her. Her old cranks were 170mm. We can definitely tell the difference. She spins faster and has more endurance. However, her power on the steep stuff where our cadence drops below about 75 is definitely reduced and we're slower there. We might go faster there with lower gears, hard to say. Overall, we're faster over the road on long rides, largely due to her improved endurance. Reducing crank length reduces power at low cadences simply because one can only push down so hard without wearing ourselves out. Pushing down with the same force at the same cadence on shorter cranks will yield less power, duh.

Generalizing from our experience, use the formula to get crank length and use those cranks. We used Steve Hoggs formula of (leg length in inches)*5.48. Don't use overall height formulas or charts - silliness. Then check your gearing on the steepest pitches you are likely to encounter.

I doubt the OP will notice much difference between 170 and 165 - only 3% difference.
I'm curious how Hogg arrived at that 5.48 formula, which would put me on 185 mm cranks (ideally, 186.3) That's not a problem for me, since I recognize it as nonsense, but on Bike Forums occasionally we encounter guys who have found Hogg's advice, or Zinn's, and are looking for ridiculously long cranks.
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