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Old 07-12-18, 10:33 PM
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Carbonfiberboy 
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Originally Posted by prathmann View Post
Based on my experience both with varying crank lengths on my singles and with various crank combinations on our tandem my answer is definitely Yes to both questions. It's inherently easier to spin high RPMs when the pedals are going around in a smaller circle and therefore slower than in a larger circle (i.e. longer cranks). And if your wife is struggling to keep up a cadence that is unnaturally high for her it could certainly be resulting in extra side-to-side body movement. Switching to a 150mm crank should make your higher cadence feel more natural to her and allow her to contribute more power instead of struggling just to keep up with the current fast pedal motion.
There's always an interesting tension in these sorts of discussions between fit and fitness.

Cadence: Sure we all have a favorite cadence range. OTOH, it's not always possible. We're not a strong team but we ride in the mountains anyway. We have been down in the 50-60 cadence range on some steep roads. We were still putting down power? You betcha, we were both about 10 beats over LTHR, probably putting down more power than we could have at 85. Cadence is simply not as important as people think it is. Higher cadence contributes to endurance but not necessarily in a single ride, more a stage race concept. It's mostly what one is used to and one can get used to most anything. Before I knew better, I rode fast centuries at below 60. See:

Crank length: See the above argument. I'm a short legged 5'6". A fitter would probably suggest 160-165 cranks. I've ridden 170 cranks forever (almost) and have 175s on our tandem. I spin them both at 95 with no problem, though I prefer to climb in the mid 80's with both lengths. There is a simple fact mentioned in the above video: the higher the cadence, the larger proportion of aerobic energy is used just moving the legs. That's not so critical for well trained riders with a high VO2max, but it is critical for those "lesser" riders among us. You can't force a high leg speed on someone with limited aerobic ability and expect a lot of power in the pedals. That's a scientific fact.

Training, pedaling ability, and body movement: Everything is trainable, even VO2max to a small degree. Leg motion is very trainable, though it takes years. Body motion has little to do with crank length and everything to do with pedaling style. I watch my shadow and have no upper body motion either on my single or tandem. The object of the pedaling game is to provide a constant torque on the bottom bracket. Said torque is the sum of the torque of both cranks, so when one crank is in its weak spot, the other is in a strong spot. On the rollers, this produces the characteristic steady whhhrrr. The effect of all this is that all pedaling forces originate in the legs. They don't travel into the upper body except under extreme effort. It's fairly easy to train someone to pedal with no upper body motion at all, using a mirror for biofeedback. Besides that, good trainer drills are pedaling steadily for 15'-45' at a cadence just a hair below bouncing or 115-120, whichever comes first. Another drill is 2 minute one-legged pedaling drills - one leg, then the other, then both legs together, repeat until legs don't work anymore. Another drill mentioned above is 3 reps of 10' hill work in a big gear at 50-55 cadence with no upper body movement at all.

Besides training both captain and stoker to be able to pedal well at various cadences, when it's all said and done, in this situation the captain is just going to have to train to produce the same power while riding at a lower cadence. It's not that hard. Probably involves some stomp and sprint intervals, low cadence work, maybe some gym work. Take @Hermes at his word. it's going to take work, patience, and time. There's no mechanical fix, only training and patience. Forget the mechanical fix.
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