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View Full Version : Crank Arm Length Myths


David Henderson
10-31-2010, 09:45 PM
Dr. James C. Martin, PhD research shows that there is little difference in efficiencies between your current crank arm length and any other commercially available crank arm length.

There are several other interesting finds from his research.

In summary: Common crank sizes are nearly all equal in efficiencies. Cranks size can be chosen for reasons such as ground clearance for cornering/obstacles (shorter), aerodynamics (shorter), or rehabilitation/flexibility (longer). Sprinting 120 rpm is best. 60 rpm is better than 100 rpm aerobically (generally lower cadences are more efficient than higher). Natural pedal stroke is best (do not pull up), crank length has no effect on fatigue, no effect on metabolic efficiencies and very small effect on maximum power. A big gear sprint is better than a small gear sprint (for 30seconds) .

For some illustrations and further comment see: http://myworldfromabicycle.blogspot.com/2010/08/dude-your-crank-lengths-fine-you-just.html

I hope this helpful.

Regards,
David Henderson

Chain of Fool
11-12-2010, 08:36 PM
Thank you for this link and your thorough explanations and generous answers to questions. I'm a transportation cyclist on a cushy seat and platform pedals. Riding any kind of a bike makes you want answers to all those questions of ergonomics because the bills for your errors are paid with your body. There are always a lot of variables and this seems to give room for superstition and opinion to muddy things up. Knocks me out that such a simple machine can get pointed attention and study for 100 years before we learn these things. Thanks for the clarity.

Makes me remember a piece of a lecture by historian Howard Zinn. Paraphrasing the punch line:
"So you see, .... an historian can get great reward/pleasure in researching and then answering some question that no one has answered before. -- But it's even more fun to find out that something that everyone thinks is true is false".

thumbprinterr
11-18-2010, 01:05 PM
generally lower cadences are more efficient than higher

i disagree with this statement. it may be true in terms of aerobic activity but not in terms of muscle fatigue or overall speed. i can almost always go much faster by spinning at a high cadence in a smaller gear than the opposite.

David Henderson
02-21-2011, 10:35 PM
i disagree with this statement. it may be true in terms of aerobic activity but not in terms of muscle fatigue or overall speed. i can almost always go much faster by spinning at a high cadence in a smaller gear than the opposite.


by the data I've studied, I would predict that your statement could be true some of the time, but not all of the time. For example: it would be true for sprinting, but not for long endurance riding.

wsbob
02-21-2011, 11:36 PM
For recreational cruising, I prefer tall gears and lower cadences for speed. It feels to me as though not having to spin so fast to keep up speed gives my legs a break. I refreshed my memory about this just the other day. I was cruising along quite well in the 52-15 chainwheel/rear cog combo. Then I decided to drop down into the 13 to see how that would go with the same or less energy expended: Who-o-o-sh! My speed picked up 7-10 mph right quick.

People's bodies work differently though. The bike, and the bodies fit to the bike also enter into what works best.

Low gears and a higher spin can be better for climbing. My imagination tells me that in that situation, the momentum of leg mass spinning around helps with forward motion.

thumbprinterr
02-22-2011, 10:23 AM
by the data I've studied, I would predict that your statement could be true some of the time, but not all of the time. For example: it would be true for sprinting, but not for long endurance riding.


i agree that it is not a hard and fast rule - results depend on a variety of factors, including terrain and body makeup/muscle type.... i think i do tend to mix up my cadence/gearing on long rides to work different muscle groups and keep my legs from getting fatigued. i also move around in the saddle for the same reasons..