The Rival AXS left crank arm features a power meter entirely contained in the DUB spindle unit for effortless integration with any bike. Just install pair and ride.Rival AXS wide aluminum left crank arm with power meter spindleSpindle-based power meter unit measures left side power to calculate total wattsLong battery life to power a season of ridesWaterproof (IPX7 waterproof to 1 meter for 30 minutes)Right crank arm Bottom bracket Spider Chainring sold separately)