how do i determine what is the best length for me? i am currently at 170 (what came on my bike) but i am not sure its the optimal length for me.
Is there a formula that should be used? what if one leg is a little longer should that be compensated using different lengths? or cleat shims?
Jonny,
the best formula I have found is…
buy whatever you find on Ebay or at the LBS that looks cool and fits your budget. Don’t worry about the length. Somewhere, someone will be able to justify whatever length you bought and tell you that what you have is exactly the correct length. The most important thing though, is that they look cool.
Good luck!
A popular formula that I have used is inseam (cm) x .21 or .216 = crank length in mm.
Make sure you measure inseam very exactly. An example of this might be someone with a 30 inch inseam. 30 x 25.4 = 762 x .21-.216 = 160-164.5. So someone with a 30-inch inseam should consider cranks from 160-165mm.
People with an inseam range of 31-33 inches probably fall within the range of crankarm lengths made by the typical manufacturer. If you are shorter or taller than this, then it might benefit you to try something new.
One noted proponent of this is Leonard Zinn, who is 6 feet, 6 inches tall and a large proponent of crank length proportional to inseam. He uses some lengths longer than 200mm according to his website.
Chad
That seems really short. Not saying your wrong, but it’s just interesting. I have an inseam of 29 but use 170s. I am getting shimano compacts soon, and was thinking of getting 170s. What benefit, if any, would there be with going with a shorter crank? I tend to spin not grind.
Crank length is one of those blatant inconsistencies that people are determined to avoid talking about. While people will go on and on about the need for the ulitmate bike fit, the difficulty of getting the proper fit and the fact that only a handful of gurus can do all the arcane calculations, everyone rides within a range of millimeters on the most dynamic piece of the equation.
Other than Zinn, everyone will just say, “You’ve got long legs, so 180’s are perfect.”
(A x 1/B) / pi / 2
or
C / pi / 2
Where…
A = overall height
B = phi = 1.61803…
C = distance from navel to the ground while standing upright, barefoot
Pi = 3.14159…
For instance…
Subject X, Joe Wiley
Standing 1770 mm tall
(1770 x 1/phi) / pi / 2 = 174mm cranks
or
1100 / pi / 2 = 175mm cranks
There you go, you’ve just witnessed the unlocking of the universe, and the reason I’m on 175mm cranks.
Here is a link to some good reading. I came across it one time and was intrigued at some of his conclusions. Again, Zinn references this page as well.
http://www.nettally.com/palmk/crankset.html
Especially look at the lies, misinformation and old wives tale page.
There is a lot of good info there that certainly makes you think. You may not agree, but it is certainly a different point of view than offered up by most traditional cyclists. I particularly like these paragraphs.
There is the inevitable argument that if this formula was correct and crank lengths should vary with leg length, surely that would have been discovered long ago. Such arguments must necessarily be based on the idea that the cycling community was more open to new ideas at some time in the past than they are today, since the vast majority of cyclists today are totally unwilling to even consider this formula much less buy a crank and try it out. I find the entire concept of an enlightened era of cycling questionable; I’ve been involved with cycling since the 1970’s, and during that time there has never been more willingness to try new ideas than there is today. In fact, in the 70’s it was all but impossible to convince a competitive cyclist to use a component that didn’t have “Campagnolo” written on it, regardless of the technical advances being offered by other companies. It would not surprise me at all to learn that the cycling community has *always *been resistant to new ideas such as crank length variations based on leg length, and that they simply have never been seriously tested. The few times they have been tried – such as tall Miguel Indurain’s use of longer cranks, revealed only after his retirement – the results seem to have been encouraging. After all, Indurain did win the Tour de France five times, and didn’t seem to suffer any adverse effects from his use of long cranks for competition.
The only real problem with the formula is that it results in crank length numbers that just don’t sound right. So, allow me to suggest this: instead of talking about crank lengths in mm, start talking about them in cm. The standard crank length is 17cm, and if you shop around you can find cranks with 17-1/4 or 17-1/2 cm lengths. These are silly variations; it would make more sense if cranks were commonly available in lengths from 15 to 19 cm in 1/2 cm increments, with custom cranks available even longer for unusually tall riders and shorter versions available for children. There, does that sound better?
She’ll let you know if its too short.
With Sojourner’s formula i came up with 175mm. With cdw’s formula i would be at 165.
right now i am riding 170, dead in the middle. hmm…