The wheel bag facilitates connecting the wheels to the bag when they are taken out of the frame. During cycling it gives you extra storage, e.g. for dirty or wet stuff. Thanks to the oval shape, you can put two wheels, with axles still in the hubs, together in one bag.
Note: only suitable for the wheels of Cyclone Trekking, Cargo and Skeleton. Chubby wheels are too big for this bag. Accessory More info