A mountain bike (MTB) or mountain bicycle is a bicycle designed for off-road cycling. Mountain bikes share some similarities with other bicycles, but incorporate features designed to enhance durability and performance in rough terrain, which makes them heavy. These typically include a suspension fork, large knobby tires, more durable wheels, more powerful brakes, straight, extra wide handlebars to improve balance and comfort over rough terrain, lower gear-ratios for climbing steep grades and sometimes rear suspension to really smooth out the trail as well as dropper-posts to quickly adjust the seat height.Mountain bikes are generally specialized for use on mountain trails, single track, fire roads, and other unpaved surfaces. Mountain biking terrain commonly has rocks, roots, loose dirt, and steep grades. Many trails have additional technical trail features (TTF) such as log piles, log rides, rock gardens, skinnies, gap jumps, and wall-rides. Mountain bikes are built to handle these types of terrain and features. The heavy-duty construction combined with stronger rims and wider tires has also made this style of bicycle popular with urban riders and couriers who must navigate through potholes and over curbs.Since the development of the sport of mountain biking in the 1970s, many new subtypes of mountain biking have developed, such as cross-country (XC), enduro, all mountain, freeride, downhill, and a variety of track and slalom types. Each of these place different demands on the bike, requiring different designs for optimal performance.