Odd crank arm length ?

[Ridgeway]

My crank arm length is 170mm, pretty sure i've had 167.5mm and even 172.5mm on my previous bike. A friend has offered me a Stages left had crank that is 172.5mm which i automatically ruled out as it's 2.5mm longer than my 170 set up.

Am i wrong in that thinking or is it worth thinking about, a thicker inner sole would probably close that gap but maybe i'm asking for trouble ?

Any thoughts

PS: i wouldn't have really given it too much thought but he's almost throwing it at me

 

[Yellow Saddle]

This is an interesting question. Sometimes, something being extremely cheap or solves a desperate problem, answers its own questions.

However, some years ago I had a customer with one leg shorter than the other. We got talking and I discover that he knew the exact shortfall in millimeters. Apparently it was something his orthopedic surgeon could measure. He said it made cycling uncomfortable. I suggested different length cranks to make up the difference.
Someone on that forum, who claimed medical credentials but remained anonymous, said it was a bad idea bla bla bla. He/she refused to explain the mechanics of why it is a bad idea. We on the other hand, could show with geometry and circles on paper, why it was a good idea and went ahead.
AFAIK, he's still cycling with his Custom Asymmetric Radius Propulsion System (CARPS) to this day and is happy with it.
Having said that, a 2.5mm inner sole will really cramp your foot in that shoe.
Also, apparently most of us have legs that don't match perfectly. Other than mine of course. My body is perfect.

 

[Shearwater Missile]

My crank arm length is 170mm, pretty sure i've had 167.5mm and even 172.5mm on my previous bike. A friend has offered me a Stages left had crank that is 172.5mm which i automatically ruled out as it's 2.5mm longer than my 170 set up.

Am i wrong in that thinking or is it worth thinking about, a thicker inner sole would probably close that gap but maybe i'm asking for trouble ?

Any thoughts

PS: i wouldn't have really given it too much thought but he's almost throwing it at me

If you have no problems with your current set up then don`t change it. If you do and then start to get problems you`d wished you had`nt changed it. FWIW I changed my left crank recently, albeit for the same size (170mm) due to damage. This new crank put my foot about 15-20mm further out than my right. I thought it would be Ok but after a couple of 20 mile or so rides I started to get a pain in groin. I bought another crank, still 170mm but this one brought my foot in, result.
If he is throwing it at you then throw it back !!

 

[ColinJ]

I broke a 175 mm left crank on a ride. (Fortunately, I was only 20 minutes from home because riding one-legged is VERY hard work!)

I had a spare left crank in my junk box, but it was only 170 mm long. Now, my left leg is significantly shorter than my right so I normally have an asymmetric posture on my bike - when I look straight down I am often virtually staring at where the left crank is attached, rather than at the top tube. It happens without me even thinking about it. I thought it might be interesting to try the shorter crank and see if that was a good match for the shorter leg...

I found it pretty comfortable! The bike ended up more upright rather than canted over to the right. I experienced less lower back discomfort than I had done with equal length cranks.

That bike is currently demoted to turbo duties. All of my other bikes have equal length cranks (two have 175 mm and the other has 172.5 mm) and riding them I am suffering the backache again. I would like to try shorter left cranks on those bikes but I can't afford to buy them. If I come across some suitable surplus cranks somewhere I will give them a go.

 

[wafter]

As someone who's had a lot of fit issues I personally think you'd be asking for trouble unless (as suggested above) you can quantify a leg-length discrepency and this somehow magically solved it.

If the crank arm is costing you next to nothing, might in not be worth swallowing a bit of extra cost and replacing your existing crankset with a used alternative of an appropriate length to suit the power meter?

 

[Venod]

Am i wrong in that thinking or is it worth thinking about, a thicker inner sole would probably close that gap but maybe i'm asking for trouble ?

It might get you to 170mm at the bottom or the 6 o'clock position but won't it have the effect of a 175mm crank at the 12 o'clock position.

 

[Hacienda71]

I had a lhs crank arm fail it was 172.5mm, I had a 175 mm spare put it on as a stop gap. It may be coincidence but I started getting frontal knee pain on one side after a week or so. It went a couple of days after I put matched cranks on.
You can get cleat shims to correct foot/leg issues.

 

[Yellow Saddle]

I had a lhs crank arm fail it was 172.5mm, I had a 175 mm spare put it on as a stop gap. It may be coincidence but I started getting frontal knee pain on one side after a week or so. It went a couple of days after I put matched cranks on.
You can get cleat shims to correct foot/leg issues.

I would have expected hip problems rather than knee problems since the two knees don't know how the pelvis is tilted.

 

[Gunk]

I swapped from a 175 to a 170 and haven’t noticed any difference.

 

[fossyant]

Don't have odd crank lengths on the bike - I assume that's what you mean.

You'll not really notice the difference. 170mm on my road bikes, and 175mm on the MTB's. Didn't notice when switching the MTB from 172.5 to 175 due to a good crankset offer. Don't have odd crank sizes on a single bike unless you've got a bio-mechanical issue that a proper bike fitter/medical person has diagnosed.

 

[mickle]

I broke a 175 mm left crank on a ride. (Fortunately, I was only 20 minutes from home because riding one-legged is VERY hard work!)

I had a spare left crank in my junk box, but it was only 170 mm long. Now, my left leg is significantly shorter than my right so I normally have an asymmetric posture on my bike - when I look straight down I am often virtually staring at where the left crank is attached, rather than at the top tube. It happens without me even thinking about it. I thought it might be interesting to try the shorter crank and see if that was a good match for the shorter leg...

I found it pretty comfortable! The bike ended up more upright rather than canted over to the right. I experienced less lower back discomfort than I had done with equal length cranks.

That bike is currently demoted to turbo duties. All of my other bikes have equal length cranks (two have 175 mm and the other has 172.5 mm) and riding them I am suffering the backache again. I would like to try shorter left cranks on those bikes but I can't afford to buy them. If I come across some suitable surplus cranks somewhere I will give them a go.

How much shorter is your shorter leg?

 

[Ridgeway]

How hard is it to shorten one leg

Looks like i'll give it a miss

 

[Hacienda71]

I would have expected hip problems rather than knee problems since the two knees don't know how the pelvis is tilted.

Might have been a coincidence but it only manifested itself when I was running mismatched cranks. Never had problems before or since. I'm no expert so just anecdotal.

 

[ColinJ]

How much shorter is your shorter leg?

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:

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.

 

[Sharky]

How hard is it to shorten one leg

Looks like i'll give it a miss

Pull the other one …...