In 1966, vehicle classification and rules were based on the SCCA’s A and B Sedan amateur classes. A Sedan was called the Over 2.0-Liter category. The cars competing in the group were limited to a 5.0-liter engine and provided a platform to showcase the new ‘Pony Cars.’ The Under 2.0-Liter category included vehicles from BMW, Alfa Romero, British Leyland and Porsche.

The Trans Am series and its regulations have evolved over time. The championship has undergone changes to the race formats, vehicle eligibility and rules governing the cars.

Currently, the races are 100-miles in length with no opportunity for a pit stop to change drivers or tires and refuel the car. Teams can also compete in two championships – Trans Am Championship and Trans Am West Coast Championship.

• Trans Am Championship – This division opened the season at Sebring International Raceway during the first weekend of March. At the end of the month, teams competed at Road Atlanta. Round three would be at WeatherTech Raceway Laguna Seca and include both championships. After the west coast swing teams would travel to Lime Rock Park, the temporary circuit at Detroit’s Belle Isle, Indianapolis Motor Speedway, Mid-Ohio Sports Car Course, Road America, Watkins Glen International and Virginia International Raceway. The penultimate weekend at Circuit of the Americas would be the second event with their west coast counterparts and the finale would take place at Daytona International Raceway in November.
• Trans Am West Coast Championship – The season started in April at Thunderhill Raceway Park and was followed two weeks later with an event at Auto Club Speedway. WeatherTech Raceway Laguna Seca hosted rounds for both championships. Then it was on to Sonoma Raceway and the penultimate event at Portland International Raceway. The finale for the west coast competitors would be another joint weekend – it would take place at Circuit of the Americas.

In 2019, there are four classes – Trans Am, Trans Am 2, Super Grand Touring and Grand Touring. Trans Am, Super Grand Touring and Grand Touring compete in the same event. Tran Am 2 drivers have their own race.

• Trans Am (TA) – This is the series quickest class. These tube-frame race cars are powered by a naturally aspirated 366-cu.in. pushrod V8 engine which produces over 850-horsepower. From a technological standpoint the vehicles are kept quite simple – no superchargers, turbochargers, anti-lock braking systems or traction control. The body styles used are the Ford Mustang, Chevrolet Camaro, Cadillac CTS-V, Chevrolet Corvette and Dodge Challenger.
• Trans Am 2 (TA2) – These are also tube-frame chassis cars. Unlike the TA category, these vehicles use electronic fuel injection and intake restrictor plates to limit the horsepower to approximately 490. To keep expenses down the maximum price for shock absorbers, wheels and brake pads and calipers are set by the series officials. For example, shock absorbers are limited to a cost of $850 each. This category is also restricted to using a four-speed manual transmission with no overdrive. Teams are also prohibited from using superchargers, turbochargers, anti-lock braking systems or traction control. The most common body style is the Chevrolet Camaro but the Ford Mustang and Dodge Challenger are also eligible.
• Super Grand Touring (SGT) – In 2019, TA3 was renamed SGT and includes a large number of production-based vehicles. Unlike TA and TA2, which is restricted to North American models, European manufacturers may also compete in this division. As a result, the list of vehicles eligible for SGT is long and ranges from the BMW M3 to the Dodge Viper. To maintain parity, some cars are fitted with restrictor plates or carry additional weight.
• Grand Touring (GT) – The newly named Grand Touring was previously called TA4. A wide range of European and American vehicles are also eligible to compete in this group – the list is not as lengthy as the Super Grand Touring category. This is viewed as an entry-level category which only allows limited preparation. To equalize performance some of the cars may carry additional weight or the engine may be fitted with a restrictor place.

Round-ten of the TA2 powered by AEM class was held at Watkins Glen International. Competitors would race for thirty-laps or seventy-five-minutes, whichever came first, around the eleven-turn 3.337-mile road course.