Stages Shimano 105 5800 Power Meter 

The 105 (FC-5800) Stages Power meter replaces the non-drive crank arm for existing 105 model cranks. Riders looking to add power to their existing crank need only select crank length. The Stages Power meter for 105 fits all styles of 105 crankset, including: compact and standard. Standard (silver) and black finishes are available.