Crank Length

I currently own a 2003 Trek 2300 bicycle, which has Shimano Ultegra 9 speed components.  Almost all of the drive train is original but, in the 6+ years I’ve owned the bike, I have put over 20K miles on it.  The components are starting to show their age.  Time for a replacement.  Since the 9 speed Ultegra components are starting to get hard to find, I was thinking I should upgrade to 10 speed.  There are no modifications to the frame, so that is not a limiting factor.  The current setup has a triple crank but, on my last trip to California, I found I did not need the granny gear.  It would save some weight, money and effort if I move back to a double.

Since I’m now talking about doing a complete overhaul of the drive train on my bike, I decided to revisit the crank length issue.  On my previous bike, a 1987 Shwinn Prelude, I had a pair of 180mm cranks.  This Trek has only 175mm cranks.  This was my only disappointment in the bike, but considering what I was gaining, I though it was a small price to pay.

Why do I think I need a 180mm cranks?  Well, I’m 6’4″ and and take a 36″ inseam in my pants.  The Trek 2300 is, and the Shwinn Prelude was, a 63cm frame measured along the seat tube.  With other bikes that I have owned I have run into problems with the bike just not fitting right, so I am very sensitive to the size of the bike.  Can I stick with the 175mm crank?  Yes, the Trek has proven that.  I do feel that I’m not getting the full power out of it?  No, I seem to be not quite as strong as I would have hoped.

Last Friday, I went down to my local bike shop and talked with the owner.  He thought I was nuts on two accounts.  The first thought he had was the cost of doing the complete overhaul. I had estimated the cost of parts to be over $1,000.  The second though he had was that I would be best to stick with the 175mm cranks and to be spinning faster.  I currently spin around 95 to 105 RPM when I’m out on the road; when I ride the trainer, I tend to grind it out since I want to work on leg strength.

So where does this leave me?  I think I have more questions than I did in the past.  Doing some research on the Internet, you find several different sites about crank length.  Should I trust them?  They sound good, but is it really just pop science behind their arguments?   Here are some of the site’s I have found:

  1. Bicycle Crank Length: A Forumla – Kirby Palm
  2. Bicycle Cranks – Sheldon Brown
  3. Bicycle Crank Length
  4. Custom Cranks for big and tall cyclists
  5. Crank Length – Bill Boston Cycles

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