ORTLIEBs classic seat bag is available in three sizes, depending on the type of tour. The small version with 49 cu.in. is an excellent fit for road applications, while the medium is perfect for mountain bikers. Size L is a true alternative to carrying a backpack, providing room for equipment, snacks, extra shells and tools for long day tours. It tucks in nicely under the saddle, and often functions as protector on bikes without fenders. The additional fixation with Velcro around the seat post provides firm and vibration-free mounting. The 100% waterproof roll closure features buckles and D-rings for locking the bag. The mounting set is also availabe as accessory.