Fit question - shorter cranks?
 

While riding one of my touring bicycles, I feel that my feet are not really "biting" the pedals as much as I can on one of my other touring bikes. The sense is that the ball of my feet are not over the axle of the pedal; I want to move my body forward to get on top of the pedals. (This is after careful fittings from two different knowledgeable bike people.)

I lived with this sensation for a year, but found, a couple of days into arduous rides, that the muscles in my legs could no longer deliver power to the pedals. Basically, I ended up using my granny gears to pedal on flat ground, and walking up hills. And when it got that bad, the only solution was to rest for a few days.

In an effort to deal with this problem, I pushed the seat forward about 10 mm (between .25 - .5 inches). Almost immediately, I regained the sense of my leg muscles efficiently transfering power to the pedals. I thought I licked the problem.

Last week, I switched to a shorter stem (to reduce upper back pain from days in the saddle). I then returned to the fellow who designed the bike and did the original fitting, and asked his opinion about the new seat position. He was concerned because my knees were 10 or 20 mm further forward than optimal; he thinks that I may experience knee problems with the seat in its new position. Now I am concerned: I have had a lot of knee problems over the years, including those that resulted from inproper bicycle fit.

Is it possible that the cranks are too long, and that I can achieve a better fit by substituting slightly shorter cranks, raising the seat a little to compensate, and pushing the seat back 10 or 20 mm to restore the original knee-pedal relation? (The two people who originally fitted me arrived at the same seat position independently, so I was reluctant to mess with it. )

Do manufacturers offer the same cranks in different lengths? I have XT cranks now.

Yes - the length is usually stamped into the backs of the arms. 170, 172.5, 175 are the most common.

If you have tried to replicate the position of your other bikes that fit well, and something still seems wrong, then crank length is a good place to start.

I understand your frustration. Bike fit can be more of an art than a science, and often by the time you figure out what was bothering you, you've gotten used to it and your other bikes feel weird. Good luck.

Not everyone uses the optimum riding position as suggested in all the bike set up articles that have been written. I am another rider that pushes the saddle forward to get cycling efficiency. Saddle too far back and I cannot get power into the back wheel. Also on crank length. I have a 29" inseam and as such- By all the set up writings, I should be using a 165 length crank. I use a 175 and a change down to 170 means that I spin a bit faster- but once again cannot get the power in on the hills.

The basic set up rules are not rules. They are guidelines. They do give you a good starting point but still have to be modified to get your body working on your bike.

If your short in stature then your issues are fammiliar with me. Sounds like you were positioned for KOPS and you've moved forward of KOPS for power and actualy this is NORMAL where your cranks are too long for an individual. Getting on top of long cranks helps most people use them. See http:/www.cranklength.info and see what they reccomend. Also see http://sheldonbrown.com/ and see frames and revisionist frame sizing for excellent info on fit.

Also what size cranks are you now using and what are you prepared to do to fix the issue. Getting your cranks custom engineered may be the way to go and its what I've done. One of the best things I've done actually.

Regards, Anthony

There are many different ways of determining crank length, but some kind of proportionality with leg length seems most sensible.

Peter White has some words of wisom as well as supplying cranks from 150-185mm from famous French manufacturer Specialities-TA.
There is a simple lookup table for length ves legs here
If you need smaller cranks, SJS cycles do cranks down to 140mm. They are not as classy as TA but a lot cheaper.