Drivers
The drivers invited were from a broad range of racing disciplines: Indy cars, NASCAR, sports car racing, and on occasion, WoO, and drag racing. Criteria for invitation was very loose, but typically consisted of recent season champions of the respective series, and individual winners of big events (Indy, Daytona, etc.)
Due to its fundamental stock car formula, and the majority of racing being contested on ovals, the series was often dominated by NASCAR participants. Also, in the small field of about a dozen cars, the share of NASCAR invitees grew over time, from just 3 drivers in the first season to 7 drivers from NASCAR-affiliated series in the last. The last non-NASCAR champion of the series was Al Unser, Jr. in 1988. Although open wheel drivers have had successes, as of 2005, drivers from road racing series had only won two races in the history of IROC (however, for many years, no "road racing" drivers were invited).
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