Bicycles have taken many forms but it was not until the second half of the 20th century that so many distinct styles became available as the bikes themselves were honed and specialised for specific sports. Mountain bikes grew out of developments in the 1970s when people started taking bikes off road and it was clear that road bikes could not cut it in the wilderness. Nowadays, mountain bikes are some of the most popular because although they are great for all-terrain riding they can also be tame enough to use each day in urban environments.
In general a mountain bike can be recognised by several key features. Good standover height and chunky tyres with plenty of grip allowing for traction on rough surfaces whilst thick, strong frames are required to take the type of punishment that is typically doled out when heading off road. Advanced gear systems are also indicative of a mountain bike with even the most basic models offering 12 to 18 different gear ratios and the top of the line bikes have 30 or more choices for riders who want real control over how a bike performs.
Many modern mountain bikes have suspension systems to complement their rugged construction. The front forks of mid range bikes will typically feature set ups that can use a combination of springs and air to soften the blows inflicted by rocky paths and jumps. Some bikes have full suspension on both the front fork and the rear shock, which gives an even greater degree of flexibility and performance whilst also offering riding comfort. You can usually adjust the suspension on advanced bikes manually, although high end products do let you alter this on the fly with handlebar mounted levers that can give you different levels of travel and increase traction as and when required.
The differing specifications of mountain bikes has led to the creation of four definable groups, largely classified as a result of their suspension set ups. Fully rigid bikes have no suspension on front or rear whatsoever and hardtail bikes are identifiable by their suspension on the front fork but not at the rear. Softtail bikes are part way towards offering rear suspension but rather than a dedicated shock, they may possess a flexible frame arrangement. Full suspension bikes, also referred to as dual suspension models, have both front and rear suspension along with a clever frame that allows for independent movement of the rear wheel. These categories should help you choose the bike you want and as you may have assumed, the bikes with more intricate suspension tend to cost more than those with more basic arrangements.
Within these categories there are other types of mountain bike that have even more specialised uses. For example, trial bikes are designed to be used not just on off road courses but in specifically built facilities where tricking and jumping require that frames are tougher and suspension more forgiving than all-round bikes. Downhill mountain bikes require light frames and are set up to be used on downhill courses rather than across all terrain types. As such, they are slack and offer up to 200mm of travel in order to protect the rider and retain traction at speed. It is possible to go on at length about the many other different types of mountain bike, but this should get you started.
