Crank length: 165 or 170mm?
10-01-16, 12:24 PM
#101
just another gosling
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I'm beginning to see the shortcomings of the analogy given that the typical staircase is steeper than the grade experienced on a bicycle. As it turns out, a 32% (17.7°) grade would make your ride fall among the world's steepest streets. The stairs of a typical house have a 60% grade.
I know there is a point where depending on the gearing some cyclists may find themselves in a situation where walking a bike up the hill may be their only option. I've been in that situation because I knew of such hills and purposefully sought them out to put the gearing of triple-ring setups to the limit. And, off-roading can get gnarly. I can't think of any of those situations where standing on the pedals saved the day over having gears that were low enough to get the job done.
So personally, I discount the role of standing on the pedals in cycling. That's just my likes and riding style. But as a result, standing on the pedals doesn't play a role for me in trying to understand the most efficient crank length.
In addition to that, I don't see stair-climbing as involving the same sort of circular motion where foot speeds vary depending on the arc described by the foot when holding rpms constant.
I know there is a point where depending on the gearing some cyclists may find themselves in a situation where walking a bike up the hill may be their only option. I've been in that situation because I knew of such hills and purposefully sought them out to put the gearing of triple-ring setups to the limit. And, off-roading can get gnarly. I can't think of any of those situations where standing on the pedals saved the day over having gears that were low enough to get the job done.
So personally, I discount the role of standing on the pedals in cycling. That's just my likes and riding style. But as a result, standing on the pedals doesn't play a role for me in trying to understand the most efficient crank length.
In addition to that, I don't see stair-climbing as involving the same sort of circular motion where foot speeds vary depending on the arc described by the foot when holding rpms constant.
One of my fitness tests is to see if I can climb a local 500' climb standing the whole way. I frequently stand when accelerating away from a stop. On long climbs, I try to stand 1 minute in every 10. I also stand frequently on flat rides. After taking a pull on a long paceline, I stand on my way to the back. I always stand when doing hill or finish line sprints.
Standing enables one to stretch legs and back, can prevent cramps, and uses different muscles through different ranges of motion than riding seated. Thus it enables a cyclist to ride longer and more comfortably.
I've never had to stand to climb any hill. I've never walked a hill except for two short, very steep hills when touring on our tandem.
I think the above is very typical of experienced cyclists. Learn to stand. It takes skill and fitness and will be good for your riding.
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10-01-16, 04:55 PM
#102
Senior Member
If Mark Cavendish only uses 170 mm it makes sense to me that I'd use shorter not longer cranks, irrespective of my greater height. Based on the research and personal experiences of many, I don't believe anyone can know for certain that a rider's height and leg length has anything to do with the body's ability to accept higher foot speeds, in a given gear and RPM.
10-01-16, 11:51 PM
#103
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If Mark Cavendish only uses 170 mm it makes sense to me that I'd use shorter not longer cranks, irrespective of my greater height. Based on the research and personal experiences of many, I don't believe anyone can know for certain that a rider's height and leg length has anything to do with the body's ability to accept higher foot speeds, in a given gear and RPM.
10-02-16, 06:33 PM
#104
Senior Member
“I used to be a big believer in long crank arms, but now I’m going in a different direction. I’m convinced that crank length and pedal rate (i.e. cadence) should be more directly related to one’s natural running cadence and stride length than anything else. Every muscle has a natural contraction rate that will yield maximum efficiency. The game is to keep the muscle in its most efficient extension range and at its most efficient rate of rotation.” ~John Cobb
10-02-16, 06:40 PM
#105
Senior Member
“[Jim] Martin conducted a study using 60 racers of all skill levels. He would vary crank length in 15mm increments, both longer and shorter. His findings showed that there was no power difference from one length to another, but that oxygen uptake was always better with shorter cranks.
“Subsequently I worked with a rider who is 6’5″, bringing his crank length down to 165mm’s over three months. He’s gained 65 watts of power.” (Ibid.)
“Subsequently I worked with a rider who is 6’5″, bringing his crank length down to 165mm’s over three months. He’s gained 65 watts of power.” (Ibid.)
10-02-16, 06:48 PM
#106
Senior Member
Is he really saying, change in paradigm? Is he crazy or something? Apparently not.
Crank Length-Coming Full Circle | Bike Crank Lengths Shorten
Since I’m predominantly a roadie who has been using a 53-tooth chainring with 175-180mm crank arms, Cobb offered that I might want to mount a 54 or 55-tooth chainring if I moved to shorter cranks.
This didn’t make sense to me – or McDaniel – initially, as it seemed to contradict the whole leverage component of the discussion. A shorter crank implies a shorter lever, which would imply that a rider need exert more force to turn the same size gear. However, Martin and his colleagues’ findings implied that longer cranks did not yield more power, and that shorter cranks yielded more efficiency in the form of less oxygen uptake. Which meant that factoring in all aspects of biomechanics and physiology, with pedal speed perhaps the most significant, the issue of leverage was no longer the primary consideration. That was the change in paradigm.
This didn’t make sense to me – or McDaniel – initially, as it seemed to contradict the whole leverage component of the discussion. A shorter crank implies a shorter lever, which would imply that a rider need exert more force to turn the same size gear. However, Martin and his colleagues’ findings implied that longer cranks did not yield more power, and that shorter cranks yielded more efficiency in the form of less oxygen uptake. Which meant that factoring in all aspects of biomechanics and physiology, with pedal speed perhaps the most significant, the issue of leverage was no longer the primary consideration. That was the change in paradigm.
10-02-16, 06:58 PM
#107
Senior Member
So, we now know that research and personal experiences exist, suggesting that leveraging biomechanics trumps mechanical leveraging alone: Use shorter cranks so that you can turn a bigger gear without working harder!
