Deore XT Power Crank I have an Ultegra Crank set. I also have a Deore XT 175mm left side power crank. Can I use this on a road bike?
Maybe.

Two considerations:


Is the interface between the crank and bottom bracket the same? It seems they would be if both cranks have a Hollowtech II 24mm spindle. Googling pics of FC-R8000 and FC-M8000 cranks the interfaces look the same.
Do the cranks have the same pedal offset from the axle? I.e., how far outboard does the crank arm push the pedal? You should be able to compare the crank arms directly.