Due to its similarity to NASCAR in tracks and cars, the series was dominated by NASCAR drivers. The last non-NASCAR champion of the series was Al Unser, Jr. in 1988. Although open wheel drivers have had successes, , drivers from road racing series had only won two races in the history of IROC. Despite its name, the IROC was closely associated with North American racing culture; its appeal to drivers from international series like Formula One was negligible, especially in more recent editions.

In 2007, IROC could not find a sponsor and postponed the first two races at Daytona and Texas. IROC went on hiatus for 2007 hoping to return with sponsor in 2008. In March 2008, IROC auctioned off its tools, equipment, cars, and memorabilia, and went out of business.

Car identification

Through 2003, IROC was also known for its rainbow of car colors being easily recognized from all other closed wheel racing series. Car numbers were utilized for scoring purposes, but were not the primary means of identification. Instead, the drivers' surname would appear on the door of the car. Exceptions were made when Mario and Michael Andretti raced in the same events. In those cases, their first name was used. The numbers would change from race to race, with the number 1 would be given to the driver starting first, and so on. The colors would correspond to the numbers. This would make it very confusing for fans, as one week their favorite driver could be driving the blue #1 car, and the next week he could be in the #5 orange car.

In 2004, the Diageo brand Crown Royal became the series' title sponsor, replacing True Value, and the procedure changed. The cars would be identically painted in white, with trim which could be changed to represent the driver's colors in his regular racing series. Further, a driver's number in IROC would be his regular number. Thus, Steve Kinser would use green trim with the #11, and Mark Martin's car would feature blue trim with a #6.

The only exception to the numbering scheme involves the number 3. Following the death of Dale Earnhardt in 2001, IROC retired the use of #3. Any driver with that regular number would use #03 instead. Helio Castroneves has raced with #03, but the car kept red trim, in reflection of his IRL car being red.

If there is a numbering conflict, another number will be substituted. In most cases, for one-digit numbers, a zero will be added in front. Otherwise a historically notable number will be run. (Penske drivers, for one instance, could use #66, owing to Mark Donohue.)

Road racing

From 1992-2005, the IROC season was exclusively run on ovals. In 2006, road courses were reintroduced to the IROC series with the cars competing on the road course at Daytona International Speedway. Also, in 2006, two drivers shared one car in an IROC first. Grand American Road Racing drivers Max Angelelli and Wayne Taylor each drove two races in 2006, trying to win the IROC title as a team, reflecting sportscar racing as a two-man team. However, in 2007, that may not have been used, as 2006 Grand American Road Racing champion Jörg Bergmeister was a solo champion. Bergmeister had to split driving duties with various drivers because his regular co-driver was forced to sit out three races because they were raced with the Indy Racing League; Colin Braun, who is 17, could not race in those three races under MSA rulings.