The Schmidt SON28 hubs are designed to provide full lighting output at a lower speed than the slightly lighter SONdelux with bikes that have 26" wheels or larger. They are also recommended if you wish to use a USB charger (see related items below) with your lights. Excellent for commuting, touring, general riding and tandems. They are not recommended for bikes with wheels smaller than 26". Schmidt hubs are the only hubs on the market with a built-in pressure adjustment system to prevent moisture from entering the hub due to expansion or contraction of the air inside the hub shell due to extreme temperature changes (like moving your bike from a cold space to a heated space, or reverse, in winter).