IMSA GT Championship

The International Motorsports Association GT Championship was the premier racing series in the United States from 1971-1998 before splitting into the American Le Mans Series and the United States Road Racing Championship. It was based primarily around road courses and especially endurance racing. However, oval conversions, or "rovals", were also used (even in the ALMS) for some time. These, however, are now used exclusively in the NASCAR-owned Grand American Road Racing Championship.