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Crank Length Question.....(5 posts)

Crank Length Question.....SevenGuy
Dec 16, 2003 2:31 PM
My wife is 5.5' with an inseam of around 30" (long for her height). She's ridden 175 cranks on her mountain bike for years-- including a couple of race seasons. Now that we are road riding more it seems that EVERYBODY I talk to says that she should ride a shorter crank. She currently has her road bike set up with a neutral knee (which she likes) and a saddle height that gives proper leg extension. She's 100 pounds and runs a compact 175 crank setup so she can spin as much as possible. She also has problems with chrondomalacia 9 (spell??) in both knees. So, to get to the point, is there a consensus on 170, 172.5 or 175 cranks?
We're appreciative of any advice.
No real answerKerry Irons
Dec 16, 2003 6:27 PM
It is generally the case that longer cranks make it harder to spin, and high cadence is the best way to minimize knee problems. That said, an extra 5 mm in crank length may only take away 3-5 rpm of spin, so it is not a large effect. A triple will help in making sure you have low enough gears to keep your cadence high while climbing - pushing hard at a low cadence while climbing is a major source of knee problems.

You will find no high quality data to support any particular crank length as being better than any other. This is true whether or not you correct for leg length, femur length, etc. What little research has been done on crank length suggests that people adapt to different crank lengths and there is no optimum or formula related to body proportion. On the other hand, you will find lots of anecdotal or low quality data to support all kinds of conclusions, and more theories than you can shake a stick at. A rider's response to changes in crank length is 1) highly individual, 2) dependent on riding style and the event (TT, climbing, crits, track racing, etc.), and 3) most important, highly adaptive. This is why it is so hard to study the effect of crank length.
No real answerSevenGuy
Dec 18, 2003 11:34 AM
Thanks for your thoughts and taking the time to reply. I certainly agree with your observations regarding the paucity of good data. I think I'll stick with the 175's and we'll try some exercises.
re: it's probably due to misalignmentcyclopathic
Dec 17, 2003 12:13 PM
I was diagnosed with chrondomalacia a over year ago, and it was fixed after corrective PT. Apparently cycling creates imbalance in muscle development (only outer part of quad used) which eventually pulls knee cup out and damages cartilage.

To remedy the problem she needs to develop inter thigh muscles. Get her thigh master (half deflated basketball or hubby would do too ;) and she needs to become Suzan Summers for 10-15min twice a day for several weeks. You should see improvement immediately; however it'll take a while for cartilage to restore, several month don't be discouraged. It'll help to take some overcounter joint supplements like glusamine, shark cartilage, etc

I'd recommend to get good sports doctor and physical therapist familiar with cycling. Hope info above helps good luck. Here's some info chondromalacia


PS. speaking of crank length I'm 5'5"/30.5" inseam, use both 170mm and 175mm. On a contrary to conventional wisdom, I spin better with 175.
re: it's probably due to misalignmentSevenGuy
Dec 18, 2003 11:33 AM
Thank you very much for the info and the link. We're going to take your advice and will start the exercises this week!