We generally view crank length as a function of femur length as compared to leg length along with foot size and pedalling style. Based on the info you gave in your very detailed post, I would say you may be in the range for 175mm. Impossible to tell for sure without measuring you. Good job on your PC training!

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Tom Demerly
The Tri Shop.com

I am predicting that in the long run PC'ers will gravitate to shorter cranks, not longer. right now you may feel like a longer crank may be "more powerful" for you but, unfortunately, on a bicycle, there is a limited gear range and so, the only way to increase speed at the top end is to increase cadence. One will have a greater capability to do this if one is on shorter cranks.

This will not be an issue until 3 - 5 years from now when you are riding 5-7 mph faster than you do now (on the flats - my prediction) and still want to ride faster yet on the downhills.

Anyhow, I think bike fitters are going to have to adjust their routine. One for non-PC trained athletes, similar to what they do now and another for PC trained athletes and vary things somewhat based upon where the client is in the training prgression. Maybe Tom could comment on that he thinks about this.

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Frank,
An original Ironman and the Inventor of PowerCranks

Dr. Day, I never really considered running out of gearing and having to run higher rpm's to continue increasing speed...that would be a wonderful problem to have!

I've always wondered why the fellow that fit me said he thought 172.5's were right for me...he also mentioned during my fitting that he thought my rpm's were "artificially too high, but, very smooth". I wondered how much of his 172.5 decision was based on my tendency to run the higher rpms, since all the bikes I look at in my size come with 175's.

Later, when he saw me riding during TT's, he told me to drop my cadence next time out...that's when I found out I was a good bit faster at a lower cadence.

I think I now know one of the reasons I am faster at lower cadences...PC's showed me how faulty my left leg was when on the rising phase...I simply was working the right leg harder to make the left one get over the top, and this inefficiency was compounded because I was still working hard to stay smooth instead of working hard to drive the chain. So, since every stroke wasted energy...if I decrease the number of strokes per minute, then I decrease the number of times I make that inefficient mistake. Bingo, more speed. There may be other reasons lower rpm's give me more speed, too. I don't really know all the physiological possibilities about that.

Anyway, that's why I'm questioning the different crank lengths. Maybe try the 175's until I can get the rpm's up higher (maybe next year?) and switch back to 172.5's then? (I'm not riding anything but the PC's for now...don't worry, Dr. Day, I'm not cheating!)

Thanks for your input!

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

I was speakign to my bike fitter a while back about this question. He mentioned that an extensive study was done with the team members of mapei... I am not sure about the specifics of the study but the results were that there was no correlation between body measurements, crank length, speed etc. and that the crank length that you were fastest on was the one that you were most comfortable on...

I wish that I could actually read the study but...
I think this discussion fits in with the discussion of topics such as cadence, eficiency, blah blah, for each person there is a technique which works best for them (pedal mashers vs. spinners)

I would be interested to hear what people (tom perhaps) feel is the intersection of crank length and bike fit. A longer crank would bring your legs higher up at the top half of your stroke thus should affect your bike fit...

Personally when I was fit we fiddled around with pedal length and damnned if I could feel a difference, or for that matter there was no measurable difference on the power output...

Interesting observation... perhaps a set of PC's are in my future.

My problem isn't that I can't spin (good lungs - bad knee)... I learned to do that some years ago. Spin became a necessity because of (you guessed it) - a knee went bad.

However, (per your observation) if your technique is inefficient and or incorrect, then a higher cadence would simply complicate this problem. Basicly, you are repeating (more frequently) the error with a higher cadence.

I might add, the knee problem was Chondromalacia (sp?). The solution to that was (basicly) refitting the bike and staying out of the big gears. More to the point, changes included a higher seat, shorter crank (albeit, only 2.5m shorter) and spin...spin...spin.

Since my options are limited, (i.e., to stay at a higher cadence), do you (or anyone) feel the advantages of PC's could improve my overall performance without the expense of knee problems?

Joe Moya

Just in case you wante to look it up

chondromalacia is the correct spelling

you spelled it correctly a previous poster spelled it slightly wrong

is almost certainly the PC's will help with your type of knee problem. I think only in the instance of unstable knee (where lifting causes abnormal joint motion) would the PC's be bad for a knee.

the only way you will know is to try and you can do so pretty much risk free because I give a liberal money-back guarantee if they don't work out.

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Frank,
An original Ironman and the Inventor of PowerCranks

See these comments by Leonard Zinn, and look at articles in velonews:

Dear Lennard;
I am a middle of the pack triathlete who at age 48 is losing speed and strength quicker than I care to admit. I am riding a Kestrel KM 40, which I have found to be the most comfortable bike yet. My question is how much is gained by going to a longer crank arm?

I presently have 175 but the local bike shop suggested 180. He stated that for time trials, a longer arm is better. If you have poor spin technique there is no efficiency lost, but extra power gained. If this is so, why isn't everyone on 180's?
Any advice is appreciated. (I am 5ft 11 in with an inseam of 29 inches.) --Bob

Dear Bob;
This is too huge of a question to tackle here. A few years back, we did several crank-length tests with an ergometer I built and using Boone and Sweet Wings cranks varying from 100mm to 220mm with riders varying from 5'2" to 6'6". With no time to get used to them, the results were inconclusive. Short cranks were more efficient at low power outputs and long ones were more efficient at high power outputs for all riders. Some shorter riders complained of knee strain with the super-long ones. In VeloNews back issues, these articles are in the April 10, 1995, April 29,1996, July 1, 1996, March 1, 1999 issues.

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"My strategy is to start out slow and then peter-out altogether" Walt Stack

Is it not unbelievable that after all these years of people in cycling and all the miles ridden and all of the computer technology that no formula works for one individual to the next. It only gives you a starting point to figure it out to your body. No matter if it is bike size, seat height, stem length, 650 or 700, or crank arm length, it can only be done by trial and error, no one person has all of the answers--no matter how good or how long they been doing it, it's all comes down to hit or miss.

I personally do nto have any opinions on power cranks...

however I would be very careful when making a statement such as "power cranks will help your problem"

Chondromalacia has several physiological, and congenital causes. Poor cycling technique can exacerbat the problem, however unless your product adresses problems such as excessive genu valgus, muscular imbalances, patellar groove problems, collagen defects, etc. etc. it will not fix this problem...

I too rode 170s many years ago but that is all we knew.About ten years ago I started riding MTBs and that bike came with 175s.When it came time to buy a new road bike I decided to match crank length.A few years later 180s on my TT bike.Now 170s on my track bike.I cant tell the diff.from one to another.I do think my seat angle is much steeper with longer cranks.Am I riding steep because of longer cranks?I'm 6' 4'' with 34'' inseam.

structural defects. But they will absolutely reduce the pushing stresses on the knee. This is one of the "complaints" we hear, that people are concerned about losing quadricepts strength.

I am a physician so I understand that nothing works all the time but as described I am comfortable that they SHOULD work in the situation described. I might point out that I did not say they would solve the problem, I said they almost certainly would. Key word almost.

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Frank,
An original Ironman and the Inventor of PowerCranks

Here is the article I was really looking for before. this one goes into depth on some testing that Zinn did on crank length using several riders over several test courses

http://www.velonews.com/tech/rev/crank.html

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"My strategy is to start out slow and then peter-out altogether" Walt Stack

This is interesting... I have read about the PC's but the point that they pushing stress is something I missed.

Moreover, I can't seem to quite get a grasp of why the PC's would remove the pushing stress. Could you elaborate (or reference a source)?

Joe Moya

In the beginning there was the heaven and earth ... no no, In the beginning, new PC users naturally hold off on the pushing while the new muscles the PC's make them use get up to speed. If they don't the cadence comes up too high and they just can't keep up for more than a few seconds, and the PC's are seriously depressing if this keeps up for more than a few days (or weeks). It seems that it takes most a full season on the PC's to be able to return to full power on the downstroke, although some seem to be able to get there faster.

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Frank,
An original Ironman and the Inventor of PowerCranks