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Except it stands to reason that the longer the crank, the harder it is to spin, even if you change the gearing to compensate, right?
And there must be a flipside to this, otherwise the ultimate crank length would be 1mm.
Kimmo-
I don't understand why having longer cranks isn't better. Greater leverage fulcrum¿ (brain can't think of the right word)of the load so easier to pedal for higher gear.
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Except it stands to reason that the longer the crank, the harder it is to spin, even if you change the gearing to compensate, right?
But you don't have to spin, because you're pushing a bigger gear. Within the ordinary range of crank lengths, your speed for a given effort is the same if the gain ratio is held constant.
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there must be a flipside to this, otherwise the ultimate crank length would be 1mm
For typical riders, biomechanical efficiency is very nearly flat (±1%) from 150mm to 200mm, but starts to drop more and more quickly outside those ranges. At the long side, it's probably an issue with range of motion, you can't apply the necessary force across such a large joint articulation angle. At the short end, you run into timing/latency issues as the muscle firing repetition rate exceeds what is viable for such a large mammal. You'd need to be a hummingbird to hit the 3000rpm necessary to exploit 5mm cranks🙂
lynx
gbj_tester
Yeah, that's just maths. It's like the difference between a 52T ring and a 53T*. Crank length is part of your overall gearing, so of course you notice a change in crank length if you don't also change some other part of the ratio chain to compensate.
When you eliminate the change in gearing, nobody can detect a 2.5mm change in crank length in blind tests. People can't even tell if their left and right crank lengths differ by 2.5mm.
* (52/53)×(172.5/170)=1.00 😀