Changed a grx to a rotor.. including crank length. do I need to review my bike fit?

In order to setup a power2max i have replaced my grx chainrings by rotor. and at the same time changed the cranks to 170mm instead of 172.5.
In theory i kept the same q-factor and used the rotor offset axle.
I am under the impression that the crankarms are further apart.
when i had the grx i could not slide a 10mm allen key between the crank and the frame (that is why i went with P2M instead of 4iiii or stages.)… now i can easily do that.
should i review the bike-fit?


  1. You swapped to a shorter crank (from 172.5mm to 170mm) which means you should raise your saddle height by 2.5mm to account for the shorter crank. This is because the pedal at the lowest point of your stroke is now “higher” and closer to the the bottom bracket. This all assumes that you were happy with your prior saddle height and associated leg extension.

  2. Related to the idea of raising your saddle to compensate for the shorter crank arm, it may be appropriate to also raise your handlebars/stem a similar mount. If you increase saddle height per #1 above, this means your handlebars are effectively 2.5mm “lower” since the saddle is higher. This can be as simple as adding/swapping a typical thin 2.5mm spacer under the stem.

  3. With respect to the Stance Width / Q-Factor you mention, I consider that a lower priority but can be worth addressing for some riders that are more sensitive to that adjustment. Without data, we are possibly talking about a small distance (=/-5mm?). It would be good for you to find that info for each crank involved. Then identify whether your new setup is wider or narrower.

    • With that info, you can either adjust the lateral position of your cleats on the shoes. You’d use half the total width change, applied to each shoe and go whatever direction compensates for the width change (narrower or wider).