29er (bicycle)

29ers or two-niners are mountain bikes and hybrid bikes that are built to use 700c or 622 mm ISO (inside rim diameter) wheels, commonly called 29" wheels. Most mountain bikes use ISO 559 mm wheels, 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".

29er rims have a diameter of approximately 622 millimetres (24.5 in) and the average 29" mountain bike tire is (in ISO notation) 59-622 - corresponding to an outside diameter of about 29.15 inches (740 mm). The typical 26" MTB tire has a rim diameter of 559 millimetres (22.0 in) and an outside tire diameter of about 26 inches (660 mm).

In the early 1980s, the size of the wheels for the emerging mountain bikes was undecided. So when English off-road cycling pioneer Geoff Apps contacted Gary Fisher and Charlie Kelly with news that he had built a prototype off-road bicycle that used large-diameter 28 x 1¾ (ISO 47-622), 47mm wide Nokian Hakkapeliitta snow tires from Finland, they were intrigued. In a letter to the December 2006 issue of Bike Biz magazine, Gary Fisher, speaking about the growing popularity of 29ers, gives his perspective: "We got some tires from Geoff Apps really early on and we [Fisher and Kelly] said ‘Holy Toledo!'" But the poor supply situation of the larger diameter tires meant the fledgling MTB industry stuck with the smaller wheel size." The first Geoff Apps-designed 700C wheeled off-road bicycle was made in 1981.

However the bicycle marketed as the Aventura by Apps' own company, Cleland Cycles Ltd, between 1982 and 1984 used the more readily available Nokian Hakkapeliitta 26 × 2 (ISO 54-584). The 650B size, also known as 27.5", reappeared in 2007 as a compromise between the 26 inch and 29 inch sizes. The 650B size is called 26", and there are several 26" tire diameters but is also known as 27.5" in 57mm and above tire widths.

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