Anyone know if the left crank arms are the same? I just got a new bike and have an XT 4iii left arm power meter from the old bike I wanted to switch over. Old bike was Boost, new bike is Super Boost. 4iii lists new XT cranks arms as 8100/8120 being the same product. Guess I can just try it and see if it fits.
They are the same arms, they just use different length spindles.
yep, it’s the same arm. It’s not just 4i who lists them as 8100/8120, it’s how they are marked by Shimano. Because they are identical. The only difference between these two cranksets (8100 vs 8120) is the chainline (52mm vs 55mm correspondingly), which results in a 6mm longer spindle and two 3mm spacers included for the latter.