Knowing how fast you're going isn't just fun; it's a key piece of data when you're putting together a training plan or proving to your friends how much faster than them you are. If you're serious about getting faster or stacking bragging rights, Garmin's Bike Speed Sensor is vital. A low-profile sensor that attaches to either hub and syncs with your Garmin Edge series computers, the Bike Speed is self-syncing, so you don't have to fiddle with it and can swap it easily between wheelsets. The hub mount means it won't interfere with your wheel's rotation, either, so you don't have to sacrifice velocity, which would defeat the whole point of such a sensor, anyway.