In the first season of Grand Am competition there were five classes but in 2005 the series had reduced the number to two categories:

• Daytona Prototype (DP): This class was introduced in 2003 and was established to replace the two existing Sports Racing Prototype groups. To control costs, the cars used a tube frame chassis rather than the expensive composites used to construct most prototype race cars. Also, expenses were contained by limiting modifications and implementing rules that would be in place for five years. Approved to produce the first generation of Daytona Prototypes - for a cost of approximately $400,000 were: Riley Technologies, Doran Designs, Crawford Race Cars, Fabcar Engineering, Chase Competition Engineering, Picchio and Multimatic. Costs were also controlled by restricting the engines to production based motors supplied by Pontiac, Lexus, BMW, Porsche, Ford and Infiniti. Engine displacement was used to determine the weight of a car and whether a five or six-speed transmission could be utilized.
• Grand Touring (GT): In 2004, there were two production-based classes: Grand Touring and Super Grand Sport which initially competed in the Grand Am Cup division. These two categories were combined into a single class in 2005. Participating in this group are manufacturers such as Porsche, BMW, Chevrolet, Mazda, Ferrari and Pontiac. As with the Daytona Prototypes, engine displacement was used to establish the weight of different makes and models.

As in the past, the season opened in January with the Rolex 24 at Daytona International Speedway and ended in Utah at Miller Motorsports Park. In between these two venues, there were events held at Autodromo Hermanos Rodriguez, Homestead-Miami Speedway, Mazda Raceway Laguna Seca, Lime Rock Park, Watkins Glen, Barber Motorsports Park, Mid-Ohio, Virginia International Raceway, Montreal, Iowa and Infineon Raceway. New for this season were Montreal and Iowa and gone from the schedule was Long Beach and Phoenix International Raceway. There was a total of fifteen events with the series competing at Daytona and Watkins Glen twice.

The 45th Rolex 24 at Daytona took place on the weekend of January 27 and 28. There was a total of 70-entries (28-Daytona Prototypes and 42-Grand Touring) which was up from previous year. Drivers would compete for 24-hours on the 12-turn, 3.56-mile track which utilized an infield road course and almost the entire tri-oval.

For the second year in a row, Daytona International Speedway management organized a press conference and photo shoot of champions and race winners competing in this year’s Rolex 24. Drivers in this group could claim five NASCAR Cup championships, six Indianapolis 500 wins, five IndyCar Series championships, one Champ Car World Series championship, nine Rolex 24 overall wins, and six Daytona Prototype championships.