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How important is crank length?(9 posts)

How important is crank length?Marty from Ottawa
Oct 17, 2002 4:03 PM
I'm in the midst of buying a new touring bike to replace my venerable Trek 520 who died in a car vrs me accident a few weeks back (sigh!).

Here's the big question: I've been using 170cm long cranks on every bike I ever owned, but now that I'm moving up to another calibre of bike, I thought I'd consider buying 160cm cranks to help me spin better - I'm 5'4" tall, and have legs that are shorter (go figure!) than most other adults.

Does anyone else out there have experience with exchanging 170cm cranks for shorter/longer ones? I've hit Peter Jon White's site, and he seems to consider that this is an important factor in bike fit. Your comments would be greatly appreciated!
Generally not importantKerry
Oct 17, 2002 5:08 PM
You will find studies that support just about any crank length for all kinds of reasons. While it stands to reason that crank length should be proportional to leg length (or some bone length), studies suggest that the human body is highly adaptable and that there is no way to predict the "right" crank length for a given person. Of course, these studies stand in stark contrast to the many THEORIES you will find presenting formulas and arguments for some methodology or another. This simply supports the "There's nothing to screw up the best theory like actual data" problem. 160 mm is pretty darn short. If you've been riding comfortably on 170s for years, you will probably still be comfortable on that length on your new bike. 165 maybe, but at 160 you might find yourself looking for new cranks in short order (no pun intended).
Formula is (top of femor to floor) X .185Marty from Ottawa
Oct 18, 2002 3:05 AM
The above forumula cited by Peter White in his very informative site's article on fitting, calls for 154.87 cm cranks for my anatomy, which I also thought were quite shorter than what a tour bike required. My logic for that thought was that a tour"ist" may have to honk a bit more than a racer, which is likely the target audience for whom the formula was produced. I therefore went up to the next available size, or 160cm. Further, Peter underscores that the above formula is merely a starting point, and that individual likes, peddling methods, etc., will dictate what works and doesn't for individuals.

As regards the difference between 160cm and 170cm, the difference is only a hair over 3/8"...and that isn't a whole lot. If I were to go with 165s, that's 3/16", which to my way of thinking would be hardly worth all the bother. Comments?

To help me out more, where can I get my hands on the studies you cited?

Tks for your help; keep it coming!
I think 165 would be the shortest, you'd better spin!Spunout
Oct 18, 2002 4:01 AM
Track sets usually come in 165. IF you are touring/commuting with a heavy load, stay with 170. Maybe you should try two lengths first.

Go to a good bike store and try them out on a trainer. I bet there is no difference. (I go to the Cyclery on Bank St., Vince is good).

My 3 cents Cdn, if you have been using 170s so far, stay there. Half the world can be wrong.
What about hills under load?McAndrus
Oct 18, 2002 12:34 PM
As Kerry said, there doesn't seem to be any hard evidence to support a realistic conclusion. Or, in other words, ask three bikers and you'll get four answers.

Conventional wisdom says longer cranks are better for climbing hills and it makes a certain sense to me. I forget my college physics but you can apply more power with the longer cranks (higher power, slower spin).

I'm not sure I'd want to try to climb a long hill under a touring load with short cranks.
Funky formulaKerry
Oct 19, 2002 6:16 AM
You may find Mr. White's site informative, but I would call it "uninformed" or "deceptive." Try the VeloNews site for a study by Leonard Zinn where he tried widely different cranks with short, averal, and tall people and found absolutely NO correlation between crank length and performance. If you Google the topic, you will find many studies, most of which conflict with each other. This alone tells the story. These formulas and theories have been around for decades, but they are just that, not proven facts. It makes no difference who the target audience is for this formula, it is not based on sound science. Plus, you will note that even the shortest (road) racer does not use anything less than 170.
re: How important is crank length?B2
Oct 19, 2002 9:55 AM
I could be way off base on this so take it with a grain of salt...

I thought that longer cranks provide more leverage and therefore more suited to steep hills and heavy loads (where you're probably going to mash anyway). It's kind of "standard" for average size persons to have 172.5 for road and 175 for mountain. If you're planning on touring with heavy loads, I would get the 170's. 160's sound really short to me! Heck can you even find 'em? Their availability should tell you something.

Bryan
It's not the size of the wand, but the skill of the magician...MXL02
Oct 21, 2002 2:14 PM
Oh nevermind...
Ask my wife! ;-b - nmgrzy
Oct 22, 2002 11:30 AM