Schwalbe has a tube locator on their website. And I think when you pull up the tires on their website the tire specs will tell you which tubes to buy. I keep a couple of spare tubes for each of my Schwalbe tires. If I recall correctly, Schwalbe makes you order tubes in pairs. Between all my bikes, I think I have Big Apples, Big Bens and Super Moto X. And varying diameters of 20", 24" and 27.5".