The two series fully merged in 2014 under the banner of the TUDOR United SportsCar Championship, with the International Motor Sports Association.

Combining classes of Sports Racing Prototypes and Grand Touring-style production-based cars, the series was centered on the Rolex 24 At Daytona but included a wide variety of American, Canadian, and Mexican tracks.

The GT classes were also simplified over the years, allowing for a variety of American, European, and Japanese manufacturers to participate including Audi, Chevrolet, Ferrari, BMW, Porsche, Ford and Mazda.

Rules allowed tuned production cars or custom tube frame chassis to be used, letting participants save cost if necessary.

Daytona Prototypes and GTs usually shared the track although do occasionally race separately, typically at shorter circuits.

The series is split into two classes known as Grand Sport (GS), intended for large capacity GT-style cars, and Street Tuner (ST), consisting of smaller sedans and coupes, some of which are front-wheel drive.

The Continental Tire Sports Car Challenge until 2013 supported some Rolex Series races but also headlined some of its own dates.

Grand-Am was the sanctioning body behind the North American arm of the international Ferrari Challenge series.

However the series was later reorganized and came under the control of the National Auto Sport Association (NASA) where it currently runs under the Formula TR name.