Odd crank arm length ?

[rogerzilla]

I have bikes from 165 to 175. I much prefer 165 (and insist on it for a fixie) but they're all fine really.

 

[rogerzilla]

Crank length doesn't really compensate for a shorter leg on one side, as it just affects the size of the pedalling circle. With a short crank, the pedal is closer at the bottom of each stroke but further away at the top! Instead, you need a thicker shoe or pedal on the short side.

 

[wafter]

I was told that the only really accurate way to tell is by having x-rays (ct scans?) done (which I haven't) but I have just had a look online and there are descriptions of various possible methods. I might have a go tomorrow. I'm not talking a HUGE difference, maybe 1.0 - 1.5 cm?

How I worked out that I had the problem...

* A friend riding behind me told me that my right knee was flicking in and out during the pedal stroke

* I was wearing out only one side of my shorts where they rubbed against the saddle, therefore I wasn't sitting normally

* The back street behind my old house had a pronounced camber. If I walked along it with my left leg near the gutter and my right leg towards the centre of the road, I felt like I was falling over to my left. If I walked back the other way I felt upright.

* I've seen photos of me riding and can see my pelvis looks tilted down on the left side and I don't look like I am sitting properly. Example:

View attachment 504214

Obviously, that one picture doesn't prove anything but I don't look straight on the bike and I have seen others similar to that.

* If I see pictures of me trying to stand up straight I often have my left heel lifted...

* My backache got really bad at one point and I went to a chiropractor. He pulled me about a bit and tried to set me out straight on his table. Unprompted by me, he suddenly announced that my left leg was 'significantly' shorter than the right and that wouldn't be helping my back.

* If I stand up as straight as I can and look at a full length mirror, I can see that my pelvis tilts down to the left and my shoulders tilt the other way as if to compensate.


When I used Look pedals and cleats I used to put about 8 mm worth of shim under the left cleat, which seemed to help. Not a practical proposition with (MTB) SPD pedal system though.

I'm probably telling you what you already know, but a mate of mine has similar issues and gets any shoes he buys built up on the short side on the NHS. Seems they do a pretty good job of matching the materials and colouring too - I certainly wouldn't have noticed had he not mentioned it.

 

[Venod]

Crank length doesn't really compensate for a shorter leg on one side, as it just affects the size of the pedalling circle. With a short crank, the pedal is closer at the bottom of each stroke but further away at the top! Instead, you need a thicker shoe or pedal on the short side.

But with a thicker sole the foot will be in the right position at the bottom it will be further from the centre line at the horizontal and even further away at the top, your knee will be higher at the top position than the other crank without the thicker sole shoe, your foot will not follow a perfect circle around the centre of the crank.

 

[Dogtrousers]

How worn is the existing chainset? You could take the offer, put it in a box and then splash out on a whole new chainset when your chainrings wear out and still not be out of pocket, and not run the risk of ending up walking in circles for the rest of your life having done weird irreparable damage to yourself due to the 2.5mm mismatch.

 

[Yellow Saddle]

But with a thicker sole the foot will be in the right position at the bottom it will be further from the centre line at the horizontal and even further away at the top, your knee will be higher at the top position than the other crank without the thicker sole shoe, your foot will not follow a perfect circle around the centre of the crank.

Correct!

 

[ColinJ]

I'm probably telling you what you already know, but a mate of mine has similar issues and gets any shoes he buys built up on the short side on the NHS. Seems they do a pretty good job of matching the materials and colouring too - I certainly wouldn't have noticed had he not mentioned it.

Thanks. I don't do an awful lot of walking, but when I do walk a reasonable distance I am usually okay so I haven't really bothered too much about built-up shoes, insoles etc.

My back gets uncomfortable when I stand still for long periods of time though. Standing on the spot would always be a problem anyway these days because my left leg has poor circulation after suffering a DVT in it and it gets swollen so I always move about every few minutes.

It's more long bike rides that cause problems. My sore back and neck limit what I can do more than my legs, lungs and heart!

(It isn't all due to the leg length issue though - I am terribly inflexible, and I'm sure that doesn't help either when bending over on the bike for 6+ hours.)

 

[wafter]

Thanks. I don't do an awful lot of walking, but when I do walk a reasonable distance I am usually okay so I haven't really bothered too much about built-up shoes, insoles etc.

My back gets uncomfortable when I stand still for long periods of time though. Standing on the spot would always be a problem anyway these days because my left leg has poor circulation after suffering a DVT in it and it gets swollen so I always move about every few minutes.

It's more long bike rides that cause problems. My sore back and neck limit what I can do more than my legs, lungs and heart!

(It isn't all due to the leg length issue though - I am terribly inflexible, and I'm sure that doesn't help either when bending over on the bike for 6+ hours.)

No worries - typical that you get away with the walking but not the riding; given which you'd rather be doing!

I find similar with flexibility; I can't get particularly low at the front and often suffer from upper back / neck pain and nasty tension headaches after a long ride; sometimes for a couple of days. I guess some stretching or yoga would probably help but I can't quite get excited enough about it to actually try it

 

[Shearwater Missile]

No worries - typical that you get away with the walking but not the riding; given which you'd rather be doing!

I find similar with flexibility; I can't get particularly low at the front and often suffer from upper back / neck pain and nasty tension headaches after a long ride; sometimes for a couple of days. I guess some stretching or yoga would probably help but I can't quite get excited enough about it to actually try it

+1 for the inflexibility and likewise with yoga. The only thing that works for me is having the bars at roughly or just below saddle height otherwise neck and shoulder pain but not the headaches. Nothing to do with crank length.