Hi all,

My bike came with the following crankset:

Shimano Ultegra SL HollowTech II 175mm crank arms w/7075 CNC 39/53T Chainrings

I want to use 172.5mm crank arms. Do I need to swap out the whole crank set or can i just replace the arms with ones that mount in the same manner? Is there any disadvantage to just replacing the arms? Is there anything that I should know before doing this?

Thanks,

Brian

I suspect you don't understand how these pieces are all connected, because what you're suggesting sounds strange. But if you have an existing set of crankarms without the chainrings, yes you can swap the chainrings between cranks.

Hollowtech II means you have to replace the whole crankset. Actually, if you could fine one without chainrings, you could swap your existing chainrings to the new crank.

2.5 mm isn't much change. When I bought the compact crank for my Klein 172.5's weren't immediately available so, after a LOT of soul searching, I ordered 175's. I couldn't tell any difference at all. None. YMMV.

I have never understood the fascination with small changes in crank arm length. In addition I have yet to see an empirical study that shows an advantage, have seen several that show no advantage, and even one person (https://www.powercranks.com/cld.html) who shows evidence that the only change that makes sense is to go much shorter. In no case do I believe from the evidence that 2.5mm is going to make enough difference to justify the expense and trouble.

Longer cranks have never made sense to me, as they increase the bend in one's knee at the top of the stroke by the same amount as lowering one's seat by double the crank length change. It is well documented that knee stress is increased as the bend in the knee is greater.