I would like to buy a 4iiii left-sided crank-arm-based power meter. I’m having trouble understanding which Shimano crank arm will be compatible with my bike. I have a Trek Madone 2 Series from ~2014 and the left crank arm is labelled “FC-R565” and “175”. I assume the “175” refers to the length in millimetres. My question is how do I figure out which Shimano crank arm I can swap in? The following are available from 4iiii: 105 FC-5800 or FC-R7000, Ultegra FC-6800 or FC-R8000, Dura-Ace FC-9000 or FC-R9100, GRX FC-RX810, XT FC-M8000, XTR FC-M9000, and XTR FC-M9020. Would any or all of these be compatible (with FC-R565) if I get one at 175 mm length?
FC-R565 is a hollowtech crank design, so any of the 105, ultegra or dura-ace crank arms you mentioned should be a straight swap. correct, you have 175mm cranks arms
Like above, 105, ultegra or dura-ace would match the q-factor. GRX and the mtb cranks would “fit” on the spindle, however then you have the wider stance on the left side - not ideal - so don’t get those even if they are cheaper!