At a feathery 325 grams, with stiff, wide flanges and a 15mm aluminum axle, the CycleOps PowerTap G3 is a fantastic hub in its own right. And, with precision electronics, it's an invaluable training tool, too! The G3 measures wattage for the ultimate objective training so you can tailor workouts and track progress. Its convenient Ant+ wireless transmission sends your critical training information to any Ant+-compatible head unit (sold separately). PowerTap readings are accurate to within +/-1.5%, so you can truly measure short, intense intervals as well as longer efforts with pinpoint precision.