Hi guys

Want to replace the crankset on my sons bike. It currently has 42,32,22 with 170mm crank arms but there is more choice with 175mm. Would the increase in size cause any serious issues? The bike is a little big for him at the moment though is is growing rapidly but don’t want to add to the size issue with pedalling issues. I am inclined to say it’s only 5mm but don’t want to damage him as I quite like him 🙂

Thanks

Might help if you say how big he is!

There’s a good number of people who say that “most” people would be better off with something smaller than the 175mm specced on almost everything.

Even though it’s only 5mm, it makes a huge difference. You don’t say how big your son is though so it’s difficult to say. Cranks that are too long can cause fatigue and knee problems.

Sorry. He’s a smidge over 5″ with long gangly legs. I think I will keep looking for 170mm or maybe even 165mm?

He’s a smidge over 5″

At a smidge over 5 inches I reckon that even 165mm cranks would be too long for him.

Seriously though, I’m about 6’4″ and use 165s as I reckon we nearly all have cranks that are too long for us so I would definitely try to get him something on the shorter side.

lol! Definitely 5 Feet. Sorry 🙂

Go for 172.5mm, they will be fine until he reaches 6’6″.

scroll down to the bottom of this page for a decent crank length calculator.

EDIT: go to the ‘crank shorteners’ page first (can’t seem to link directly), then scroll down.

FWIW, but I was getting knee pain with 175mm cranks. I replaced them with 170mm and i’ve not suffered any pain since. I’m 178cm with “normal” length legs.

I didn’t actually feel much difference whilst riding other than the lack of pain. No noticeable difference in performance/efficiency either.

Thanks for the link Mr Kettle. It’s very useful. The real problem seems to be a lack of anything other than your ‘Standard’ 170/175mm offerings if buying a complete crankset.

IM(and many others’)E makes no difference – but others find even 2.5mm life changing as above.