UTFG (Use The Fucking Google) - daj tam napr. 27.5 inch bike 
Tie udaje o 26", 27.5" resp 29" su rozmermi aj s pneumatikou. Ta moze byt rozna a preto nie su presne. Prezil som jednu vasnivu hadku na tu temu a nasiel normu. http://en.wikipedia.org/wiki/Bicycle_wheel Tu mas citat (citát):
Mountain bike wheels
A 29" and 26" Mountain Bike wheel
26 inch wheel/ISO 559
26-inch clincher tires (with inner tubes) are the most common wheel size for mountain bikes. This tradition was started initially because the early mountain bike pioneers procured the wheels for their early bikes from American-made bicycles rather than the larger European standards in use. The typical 26-inch rim has a diameter of 559 mm (22.0") and an outside tire diameter of about 26.2" (665 mm). Increasingly common are tubeless tires conforming to the UST (Universal System Tubeless) standard pioneered by French wheel manufacturer Mavic in conjunction with tire manufacturers Hutchinson and Michelin.
29 inch wheels/ISO 622
Main article: 29er (bicycle)
“29-inch wheels”, which also conform to the popular 700C (622 mm diameter clincher wheel standard) are becoming more popular for not only cyclocross bikes but also cross-country mountain bikes for larger riders. Their rim diameter of 622 mm (~24.5 inch) is identical to most road, hybrid, and touring bicycle wheels, but are typically reinforced for greater durability in off-road riding. The average 29-inch mountain bike tire has an outside diameter of about 28.5" (724 mm). There are advantages and disadvantages associated with this change discussed in detail in the main article.
a nasiel normu. http://en.wikipedia.org/wiki/Bicycle_wheel Tu mas citat (citát):Mountain bike wheels
A 29" and 26" Mountain Bike wheel
26 inch wheel/ISO 559
26-inch clincher tires (with inner tubes) are the most common wheel size for mountain bikes. This tradition was started initially because the early mountain bike pioneers procured the wheels for their early bikes from American-made bicycles rather than the larger European standards in use. The typical 26-inch rim has a diameter of 559 mm (22.0") and an outside tire diameter of about 26.2" (665 mm). Increasingly common are tubeless tires conforming to the UST (Universal System Tubeless) standard pioneered by French wheel manufacturer Mavic in conjunction with tire manufacturers Hutchinson and Michelin.
29 inch wheels/ISO 622
Main article: 29er (bicycle)
“29-inch wheels”, which also conform to the popular 700C (622 mm diameter clincher wheel standard) are becoming more popular for not only cyclocross bikes but also cross-country mountain bikes for larger riders. Their rim diameter of 622 mm (~24.5 inch) is identical to most road, hybrid, and touring bicycle wheels, but are typically reinforced for greater durability in off-road riding. The average 29-inch mountain bike tire has an outside diameter of about 28.5" (724 mm). There are advantages and disadvantages associated with this change discussed in detail in the main article.
