My knees are killing me...

[OakLeaf]

Does it say somewhere on the crank? It is not listed in the specs on the trek site.

On my 105 cranks it's stamped on the inside of the right crankarm just above the pedal.

I don't know whether there are any good rules for choosing crankarm length. Maybe Knott or someone can weigh in? One of these days I'm going to pick up Andy Pruitt's book It's not just your leg length, it's the tibia/femur ratio (which can't be measured very accurately without X-rays), but a fitter should be able to check your knee angles at both the top AND the bottom of the stroke.

[Cataboo]

It should say around the pedals on the inside of the cranks.

I'm 5'1 and use 165 cranks. The smaller the cranks, the easier it is to spin - and it's usually easier on your knees.

This has some info on cranks and what size they should be.
http://www.nettally.com/palmk/crderiva.html

I get knee pain when I've tried 170 and 172.5 mm cranks

[arielmoon]

It says 172.5.

I am 5'7. 31" inseam. Plugged into that formula puts me at 169.88.

Very interesting info! Thanks for the link!

[Cataboo]

It says 172.5.

I am 5'7. 31" inseam. Plugged into that formula puts me at 169.88.

Very interesting info! Thanks for the link!

My bf's 5'7 - he's got a 33 inch inseam. He uses 170 cranks. He definitely doesn't like 172.5 cranks. He can use 165's, but prefers 170 because he's used to mountain biking.

Too long of cranks will definitely stress your knees - Pay attention to the angles your knees make when you're pedaling - does your knee come above the horizontal, things like that.

[arielmoon]

Thanks for the input Catriona!

After playing around with the adjustments and still not getting relief I am going to call LBS today and have them order me a shorter crank arm set.

Thanks everyone. I will keep this thread posted with how it goes!

[arielmoon]

UPDATE: I called and talked to one of the other mechanics and he claims that 2.5mm is not going that much of a difference on the crank. He was not open to the idea to say the least.

He says the shop has shoe shims that we can try but he really wants me to come in and get re fitted. He is the head mechanic and is a very strong, experienced rider.

I am going to try to do that this week but I am also considering this guy I heard about that does a bike studio fit. Not cheap but really helped a rider I know of.

[OakLeaf]

With you needing to limit the range of motion of your knees, you may well need shorter crankarms than 170.

When you go back to the LBS, have your fitter measure the angle of your knees at the top of the pedal stroke as well as the bottom. Remember that shimming the cleats will mean bending your knees MORE at the top. Not a good thing for those of us with kneecap tracking issues.

Do you have a friend with a smaller bike you could try out and just see how their cranks work for you? Or would the shop let you test ride one? I'd let you ride mine (you'd have to raise the seat WAY up ) but we won't be down there for at least another month.

PS - 2.5 mm doesn't seem like it should make a lot of difference, but neither does 5 mm, and 5 mm makes an ENORMOUS difference to my knees. I demo'ed a bike with 167.5 mm cranks when I first returned to road riding, and while my knees were okay with it, I felt like I had to set my seat height way high and ankle quite a bit to protect my knees.

[aicabsolut]

UPDATE: I called and talked to one of the other mechanics and he claims that 2.5mm is not going that much of a difference on the crank. He was not open to the idea to say the least.

He says the shop has shoe shims that we can try but he really wants me to come in and get re fitted. He is the head mechanic and is a very strong, experienced rider.

I am going to try to do that this week but I am also considering this guy I heard about that does a bike studio fit. Not cheap but really helped a rider I know of.

It says 172.5.

I am 5'7. 31" inseam. Plugged into that formula puts me at 169.88.

Very interesting info! Thanks for the link!

I'm 5'7" with about 31.5" inseam. My bike came with 175mm crankarms for some unknown reason. Once they changed them to 172.5mm, it was heavenly. I really noticed those millimeters! That said, with your stats, I wouldn't go shorter than 170mm. Eventually, you're going to start losing noticeable torque.