The International Motor Sports Association, IMSA, is the top tier of endurance auto racing in the United States. The series holds four endurance races within their 11 race season, which comprise the prestigious Endurance Cup Championship. This championship within a championship is contested by race teams from all across the world. The season begins at Daytona International Speedway with the Rolex 24, a 24 hour test of teams and machines. The following race is the 12 Hours of Sebring, which due to the toughness of the circuit is just as grueling although half the duration. Summer has the historic 6 Hours at Watkins Glen. Finally, the season wraps up in October at Road Atlanta with the 10 hour Petit Le Mans.
The series competes with four classes of cars at the same time. Each class is racing for their respective class victory. To help the fans follow the racing action, each class carries a different color on the cars' number plates, door mirrors, and rear wing endplates. The top class GTP cars use black, LMP2 cars use blue, GTD Pro cars use red, and GTD cars use green to differentiate their classes. To further assist the fans there are LCD panels on each side of the car which display the car's current position in class.
Grand Touring Prototypes (GTP) are the most sophisticated and fastest cars of the endurance racing world. They are built from a carbon fiber chassis available from three manufacturers. They are then covered with carbon fiber and Kevlar bodywork representing individual car companies. They are powered by 650-700hp engines coupled to a hybrid motor. They are capable of exceeding 200mph depending on setup and track. Drivers in this class are some of the best professional racers in the world.
Le Mans Prototype 2 (LMP2) are the second fastest cars on track. They are built from carbon fiber chassis and carry standard composite bodies that are spec pieces per chassis manufacturer. This class uses a 500hp spec V-8 engine supplied by Gibson. Drivers in this class are a blend of high talent professional and lower level "gentleman" drivers. All drivers are ranked by an international organization, Platinum drivers being the best then Gold, Silver, and Bronze. LMP2 teams must have a Bronze driver.
Grand Touring Daytona Professional (GTD Pro) is a class of racers based on production sports cars. They must use a certain percentage of production car parts and meet a series homologation process to compete. They have various engine types and sizes. To ensure close competition IMSA uses a system called Balance of Performance. This analyzes car performance and dictates weight changes and engine restrictions to equalize the GTD Pro field. The drivers in this class can all be top-level professionals.
Grand Touring Daytona (GTD) uses the same class of cars as GTD Pro. The cars use the same Balance of Performance system also. The drivers are a blend of professional and "gentleman" drivers. Each GTD team must include a Bronze driver. In the IMSA series 10 different manufacturers are represented. The cars are the Acura NSX, Aston Martin Vantage, BMW M4, Chevrolet C8 Corvette, Ferrari 296, Lamborghini Huracan Evo2, Lexus RC-F, McLaren 720S, Mercedes-Benz AMG, and Porsche 911 GT3.R.
The accepted birthplace of endurance racing in the United States is Sebring International Raceway. The track was built from a former WWII airfield, with the main straights still being comprised of concrete poured in 1941. The facility hosted the first endurance race in the U.S. in 1952, the 12 Hours of Sebring. Other sports car racing tracks in America added endurance races in years to follow. The first endurance race at Daytona International Speedway was held in 1962. The race was the 24 Hours of Daytona, which is now known as the Rolex 24. In 1968 Watkins Glen International added its 6-hour enduro. Thirty years later the fourth big race was added. Under the flag of an IMSA rival the Petit Le Mans was first run in 1998 at Road Atlanta. The race was a 1000 mile or 10-hour event, whichever came first. It has since changed to a set 10-hour endurance race.