Crank alignment (possibly bent left side crank)

[Dan_Marshall]

Hi all,

Looking to get a bit of advice if I may....

Is there a way to measure / find out if my left hand side crank is slightly out of shape? The reason I ask is that I have been having a slight niggling pain in the top half of my calf (left hand side) and I am associating this with my leg not tracking straight through the pedalling motion. This is on a Giant Defy and using an 8 speed claris crankset with octalink BB

I have checked my cleats (SPD - M089 shoes) and they are correct as I use these shoes on my other 2 road bikes without issue and very comfortable.

The crank to me looks a little outward (from the frame) from a 90 degree angle level to the ground but no movement within the unit (not loose / wobbly) and would like to know if there is a way to measure it properly to confirm it either being the crank (or perhaps even the bottom bracket) that is out of line.

Thanks

 

[S-Express]

Very unlikely that the arm is bent, given that it is a huge lump of cast aluminium designed to withstand significant loading. Could be any number of potential reasons for a calf niggle, and no guarantee that any of them are bike related.

 

[Dan_Marshall]

Thanks for the reply - FWIW one of my other bikes has the same groupset / crankset on it and when using riding this bike (same shoes as well) there is no pain.

Set up of the bikes is identical (saddle height, fore/aft relating to BB, reach etc).

 

[S-Express]

If it is the same groupset, then you should be able to easily tell if one arm is bent (compared to the arm on the other bike) or not.

 

[User6179]

Check the gap between the chainstays and the crank , when I changed my CAADX crank I noticed the gap was bigger on one side , turns out I had did about 3000 miles from new with the left hand crank not fitted properly .

 

[User33236]

Mrs SG was having a problem with one of her bikes which recently had a crankset transferred to it from one of mine that had been written off after being hit by a car.

Visually the left crank arm looked perfect but on very close inspection, and comparing it with a new arm off another bike, it was found to have a slight bend in it. It was replaced and her problems went away.

 

[fossyant]

Cranks are never 90 degrees. They all splay outwards slightly

 

[Dan_Marshall]

If it is the same groupset, then you should be able to easily tell if one arm is bent (compared to the arm on the other bike) or not.

This is my issue - if it is out (as I expect it to be) then it is only out very very slightly, and not noticable until well into a ride 10-15 klms when the mild niggle starts up and I am stumped on how to measure the crank arm to identify / eliminate that this is in fact the cause.

Looking at the other bike's left hand crank when parallel to the ground, and then with the 'issue' bike, the cranks look the same. However, if the left crank is bent slightly and offset by 1-2mm then there would be significant side to side movement through the pedal stroke which could be the root of my issue. That's why I ask if there is a way to measure the crank arm

Check the gap between the chainstays and the crank , when I changed my CAADX crank I noticed the gap was bigger on one side , turns out I had did about 3000 miles from new with the left hand crank not fitted properly .

So the right side crank parallel with the right chainstay should be the same distance apart as the the left side crank parallel with the left chainstay?

 

[User33236]

Take off both crank arms and place then on a flat surface and check for differences.

I had to end up doing that to confirm the one Mrs. SG had was bent.

 

[davidphilips]

check your saddle

saddle height

as dan said recheck your saddle hight a saddle even a half inch to high will put a lot more strain on your lower legs, best to perhaps lower it a bit and retry after a few days rest to see if pain goes away.

 

[andrew_s]

Very old cranks are often 90 degrees, mostly those early enough to be modelled after cottered cranks, like the Stronglight 49D.

The only real way to tell if a crank is bent is to compare it to a new or known good crank of the same model and length. Do something like clamp the pedal faces to a bench, and compare the positions of the BB end.

Another thing to check for would be a bent pedal axle.
If it's only a bit bent, it's probably easiest just to swap pedals with another bike and see whether that moves the problem or not.

 

[User6179]

This is my issue - if it is out (as I expect it to be) then it is only out very very slightly, and not noticable until well into a ride 10-15 klms when the mild niggle starts up and I am stumped on how to measure the crank arm to identify / eliminate that this is in fact the cause.

Looking at the other bike's left hand crank when parallel to the ground, and then with the 'issue' bike, the cranks look the same. However, if the left crank is bent slightly and offset by 1-2mm then there would be significant side to side movement through the pedal stroke which could be the root of my issue. That's why I ask if there is a way to measure the crank arm


So the right side crank parallel with the right chainstay should the same distance apart as the the left side crank parallel with the left chainstay?

Yes the gap should be the same .

 

[Dan_Marshall]

check your saddle


as dan said recheck your saddle hight a saddle even a half inch to high will put a lot more strain on your lower legs, best to perhaps lower it a bit and retry after a few days rest to see if pain goes away.

That was me

Saddle height is correct and Identical in set up with the other bikes where there is no issue - Had a bike fit approx 4 months ago and no probs with fit, cleats, shoes reach etc.

 

[Dan_Marshall]

Yes the gap should be the same .

Will give it a try this afternoon and report back

 

[Dan_Marshall]

Very old cranks are often 90 degrees, mostly those early enough to be modelled after cottered cranks, like the Stronglight 49D.

The only real way to tell if a crank is bent is to compare it to a new or known good crank of the same model and length. Do something like clamp the pedal faces to a bench, and compare the positions of the BB end.

Another thing to check for would be a bent pedal axle.
If it's only a bit bent, it's probably easiest just to swap pedals with another bike and see whether that moves the problem or not.

Never thought of the pedal axle being bent but will give it a look over as well - Thanks