the ultimate jockey wheel with Enduro XD-15 bearings. Not only 1 gram lighter each than the super light ZERs, these will outlast your derailleurs lifespan! They will spin with the same speed years from now, as fast as the day you installed them. When installed with our XD-15 bottom bracket and XD-15 wheel kit, these complete the ultimate Enduro Bearings Speed Kit for your bike, reducing the overall friction to almost nothing.