Mountain bike forks often contain a set of shocks, in which case the fork blades typically consist of upper and lower telescoping tubes, which are called 'legs.' The suspension travel and handling characteristics vary depending on the type of riding the fork is designed for. For instance, manufacturers produce different forks for cross-country (XC), downhill, and freeride riding. Forks designed for XC racing are typically lighter and have less suspension travel than those designed for rougher terrain and more extreme conditions. Suspension fork design has advanced over the years with suspension forks becoming increasingly sophisticated and diverse in design. When suspension forks were introduced, 80-100mm of travel was deemed sufficient for a downhill mountain bike. Typically this amount of travel is now used in XC disciplines, with downhill forks now offering 150 to 200mm of travel for handling extreme terrain. Fork travel is also dependant on your frame, to optimise the handling of your bike it is best to stick to within the manufacturers guidelines, if you choose to use a fork with too much or too little travel you could upset the handling of your bike so the steering feels 'twitchy' or 'unresponsive'.