29ers or Two-niners are mountain bikes that are built to use 700c or ISO 622 mm wheels. Most mountain bicycles use ISO 559 mm wheels which are commonly called 26" wheels. The ISO 622 mm wheel is typically also used for road-racing, trekking, cyclo-cross, touring and hybrid bicycles. In some countries, mainly in Continental Europe, ISO 622 mm wheels are commonly called 28" wheels or "28 Incher".