The AMA Motocross Series (commercially known as AMA Pro Motocross) is an American motorcycle racing series. The series is the major outdoor motocross series in the United States and is sanctioned by AMA Pro Racing and managed by MX Sports Pro Racing. It is the successor to the Trans-AMA outdoor motocross series held from 1970 to 1981.
Following the rise of Scrambles racing in the US during the 1950s, 1961 saw the AMA Competition Commitee establish their own rules for moto-cross which had been popular in Europe for years. The rules changed the scoring system to be more in line with motocross in the FIM.
The 1970 inagural Trans-AMA season was organized by the AMA, partially in response to the 1970 Inter-AM Motocross Series, but more importantly, to allow more American riders to race against European stars. At the end of the first season British riders owned the podium with 1, 2 and 3 in the standings. The following year Mark Blackwell (500cc) and Gary Jones (250cc) whould be declared American champions based on points.
Finally, the AMA professional motocross series was sanctioned for the 1972 season with the introduction of two classes based on 500 cc and 250 cc engines. For the first year points were combined with the results in the Trans-AMA 500cc class to determine the 500cc AMA Motocross champion. Brad Lackey was crowned the first AMA Motocross champion in the 500cc class with Gary Jones taking the 250 crown.
Meanwhile Americans had come of age as professional racers with the 1975 sweep of the Inter-AM Series by Tony DiStefano. At the same time Roger De Coster single handedly prevented the Americans from taking the Trans-AMA series until 1979 when Bob Hannah started the run of American dominance of that event until its cancelation in 1982. The Pro Motocross series steadily gained in popularity as Bob Hannah won 66 races and six national championships in the span of eight years. He was followed by the 41 wins and four titles of Mark Barnett and 40 wins and six titles for Broc Glover.
A 125 cc class was added for the 1974 AMA Motocross National Championship season. As motocross technology developed, 500 cc two-stroke motocross bikes became too powerful for the average rider and, faced with diminishing numbers of competitors, the AMA discontinued the 500 cc class after the 1993 season. A women's national championship series was introduced in 1996.
Facing tightening federal emissions regulations in the United States, the A.M.A. increased the allowable displacement capacity for four-stroke engines in 1997, in an effort to encourage manufacturers to develop environmentally friendlier four-stroke machines. Due to the low relative power output of four-stroke engines, compared to the then-dominating two stroke design, the AMA had increased the allowable displacement capacity for four-strokes. By 1994, the displacement limit of a four-stroke power motocross bike was up to 550 cc in the 250 class, to incentivize manufactures to further develop the design for use in motocross.
In 2006, the 250 cc division was renamed the MX Class, with an engine formula allowing for 150–250 cc two-stroke or 250–450 cc four-stroke machines. The 125 cc class was renamed the MX Lites Class, allowing 0–125 cc two-stroke or 150–250 cc four-stroke engines. In 2009, the MX class was renamed the 450MX Class and the MX Lites Class was renamed the 250MX Class, to reflect the fact that all the competing manufacturers had adopted four-stroke machinery.
For Supercross see AMA Supercross Championship.
With respect to the MXGP holding the discipline's worldwide title, and the advent of the FIM Supercross World Championship resulting in the AMA Supercross Championship losing its world title status, the two series will form the SuperMotocross World Championship from 2023.
AMA women's Motocross Championship (WMX).
AMA Amateur National Motocross