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Though originally denoting a bicycle intended for BMX Racing, the term "BMX bike" is now used to encompass race bikes, as well as those used for the dirt, vert, park, street, flatland and BMX freestyle disciplines of BMX. BMX frames are made of various types of steel, and (largely in the racing category) aluminum. Cheaper, low end bikes are usually made of steel. High range bikes are mostly chromoly or high tensile steel, although the latter is noticeably heavier with respect to strength. High-performance BMX bikes use lightweight 4130 chromoly, or generation 3 chromoly.
The introduction and widespread popularity of the cassette hub has ushered in the use of smaller gearing on BMX bikes. Instead of the old 44/16 gearing found on almost all older BMX bikes, new bikes use gearing such as 36/13, 33/12, 30/11, 28/10, 25/9, 23/8,and even 22/8, all of which have similar gear ratios of almost 2.8:1. Advantages of smaller gearing hubs include lighter weight, and more clearance when grinding. The freewheel hub is all but extinct due to several factors. The smallest freewheels that can be made is with 8 teeth, which is smaller than most riders prefer. Also, they are less consistent than cassette hubs, and skip or jam up far more frequently.
On most freestyle, street, and park BMX bikes, the wheels have 36 spokes, with more aggressive riders using 48 spoke wheels, due to the extra strength afforded them. Race bike wheels are also usually 36 spokes, but wheels for the smallest racers, sometimes as young as three years old, can be built with 18 or 28 spokes.
BMX Racing bike wheels vary in size, from 16" to 26", with 20" being the most popular.
Dirt jumping and freestyle bike wheel sizes include 16" and 18" for younger, smaller riders, 20" for most other riders, and a few companies including Haro and Sunday offer 24" freestyle bikes for taller or older riders who feel cramped on a standard 20" BMX bike.
BMX started in the early 1970s when children began racing their bicycles on dirt tracks in Southern California, drawing inspiration from the motocross superstars of the time. The size and availability of the Schwinn Sting-Ray made it the natural bike of choice, since they were easily customized for better handling and performance. BMX racing was a phenomenon by the mid-1970s. Children were racing standard road bikes off-road, around purpose-built tracks in California. The 1972 motorcycle racing documentary "On Any Sunday" is generally credited with inspiring the movement nationally in the US; its opening scene shows kids riding their Schwinn Stingrays off-road. By the middle of that decade the sport achieved critical mass, and manufacturers began creating bicycles designed especially for the sport.
George E. Esser founded the National Bicycle League as a non-profit bicycle motocross sanctioning organization in 1974. Before they set up the NBL, George and his wife, Mary, promoted motorcycle races with the AMA (American Motocross Association), and through their "National Motorcycle League," or NML. Their two sons, Greg and Bryan, raced motorcycles, but also enjoyed riding and racing BMX with their friends. It was their sons’ interest, and the absence of an Eastern presence by the National Bicycle Association (NBA, at the time the only sanctioning body of BMX Racing), that prompted George to start the NBL in Florida.
By 1997 the American Bicycle Association (ABA) was organized as a national sanctioning body for the growing sport. In April 1981, the International BMX Federation was founded, and their first world championships were held in 1982. Since January 1993 BMX has been integrated into the Union Cyclist International (UCI).
BMX Freestyle (which, today, encompasses the Dirt, Vert, Park, Street and Flatland disciplines) was created by racers who enjoyed pushing the stylistic limits of what they could do on their bikes. Haro Bikes founder Bob Haro is popularly known as "The Father of Freestyle"
BMX Freestyle is now one of the staple events at the annual Summer X Games Extreme Sports competition and the ETNIES backyard jam, held largely on both coasts of the United States. The popularity of the sport has increased due to its relative ease and availability of riding locations. At the games, Latvian Māris Štrombergs and Anne-Caroline Chausson of France were crowned the first Olympic champions in Men's and Women's BMX Racing, respectively.
Some BMX riders go on to other cycling sports such as such as Australian Olympian Jared Graves, former "golden child" Eric Carter, and youth BMX racer Aaron Gwin. Conversely, Mountain Bike racers sometimes cross over to BMX Racing, such as 2008 Olympic Bronze Medallist Jill Kintner of the USA.