SRAM cut grams out of their Rival aluminum crankarms, but didn&&';;t cut corners on power measurement. The light and accurate spindle-based power unit nestles into the striking redesigned arms to give you the data you need, and our newest direct mount chainrings are light and stiff while looking good. Spindle-based power meter unit measures left side power to calculate total watts Long battery life (400+ hours) to power a season of rides (User replaceable AAA lithium battery) IPX7 waterproof to 1 meter for 30 minutes X-Sync wide-tooth, narrow-tooth aluminum chainring technology provides maximum chain control Carbon fiber crankarms are incredibly strong and lightweight DUB bottom bracket adds durability and simplicity (Bottom bracket sold separately)