Ortliebs classic saddle bag comes in three different sizes to match the needs of your ride tour or trip the small 08l pack is ideal for road bikes the medium at 13l is great for mountain bike excursions and the 27l large is a genuine alternative to taking a backpack with youthe dimensions are thought out fully so they fit well under the saddle and the larger sizes even offer protection to the rider when the bike doesnt have mudguards your kit will stay clean and dry thanks to the water