Throughout the 1990s and first decade of the 21st century, mountain biking moved from a little-known sport to a mainstream activity. Mountain bikes and mountain bike gear, that was once only available at specialty shops or via mail order, became available at standard bike stores. By the mid-first decade of the 21st century, even some department stores began selling inexpensive mountain bikes with full-suspension and disc brakes. In the first decade of the 21st century, trends in mountain bikes included the "all-mountain bike", the 29er and the singlespeed. "All-mountain bikes" were designed to descend and handle well in rough conditions, but still pedal efficiently for climbing, and were intended to bridge the gap between cross-country bikes and those built specifically for downhill riding.
They are characterized by 4–6 inches (100–150 millimetres) of travel. 29er bikes are those using 700c sized rims (as do most road bikes), but wider and suited for tires of two inches (50mm) width or more; the increased diameter wheel is able to roll over obstacles better and offers a greater tire contact patch, but also results in a longer wheelbase, making the bike less agile, and in less travel space for the suspension. The single-speed is considered a return to simplicity with no drivetrain components or shifters but thus requires a stronger rider.
Following the growing trend in 29-inch bikes (29ers as stated above), there have been other trends in the mountain biking community involving tire size. One of the more prevalent is the new, somewhat esoteric and exotic 650B (27.5 inch) wheelsize, based on the obscure wheel size for touring road bikes. Another interesting trend in mountain bikes is outfitting dirt jump or urban bikes with rigid forks. These bikes normally use 4–5" travel suspension forks. The resulting product is used for the same purposes as the original bike. A commonly cited reason for making the change to a rigid fork is the enhancement of the rider's ability to transmit force to the ground, which is important for performing tricks. In the mid-first decade of the 21st century, an increasing number of mountain bike-oriented resorts opened. Often, they are similar to or in the same complex as a ski resort or they retrofit the concrete steps and platforms of an abandoned factory as an obstacle course, as with Ray's MTB Indoor Park. Mountain bike parks which are operated as summer season activities at ski hills usually include chairlifts which are adapted to bikes, a number of trails of varying difficulty, and bicycle rental facilities.
