As a sport or a hobby, mountain biking can be split into 9 different categories. These categories are very versed in what they offer. They are:
BMX
BMX is a style where the bikes offer 20 inch wheels. These bikes are commonly used at skate parks or with dirt jumps. Because of their smaller wheels and shorter wheel bases, BMX bikes are much easier to perform tricks and stunts with.
Cross country
This type of mountain biking involves riding your bike up and down hills. Although it's the least extreme form of mountain biking, most cross country riders are very fit and go on long rides.
Cyclo cross
This is a cross between road and mountain biking. These riders have to go over obstacles, cross through rivers, and race on and off the course.
Dirt jumping
Dirt jumping involves jumping the bike over large man made dirt jumps then doing tricks while they are in the air. These jumps are normally close together so riders can go over six or more jumps in one run, gaining a flow to give them more speed for bigger jumps.
Downhill
Downhill mountain biking involves racing downhill as fast as possible. This type of riding is very intense and extreme, offering riders the chance for ultimate thrills and excitement.
Freeride
Free riding involves finding the perfect line down the mountain using all of the terrain to express yourself. These competitions are very popular, as riders can express themselves any way they see fit.
Single speed
No to be confused with fixed gears, this is a form of cross country biking that's done using a bike with only one gear and fewer components. The idea with single speed is simplicity. The straight chain line will provide efficient pedaling, and the lack of components mean less mechanical problems and a lighter bike.
Street and urban
This type of riding involves riding in urban areas, ledges, and other types of man made obstacles. Riders of street and urban biking will do tricks as well, such as stalls and grinds.
Trails
Trials are considered an aspect of mountain biking, although the bikes used look nothing like mountain bikes. They use 20 or 26 inch wheels and sport small, low frames. Trail riders will hop and jump their bikes over obstacles, which requires an extreme amount of balance and concentration.