Oklahoma International Raceway (or OIR) is a two-configuration, crossover road course in Mustang, Oklahoma.
OIR two configurations, the GP Circuit and the North Loop.
The track heads due west on the front straightaway, which is a long, gentle downhill slope. Just before reaching Turn 1, the track levels out.
Turns 1 and 2 together form a 180-degree right-hand carousel. Turn 1 is a sweeping 45-degree right-hander that leads into the far sharper 135-degree Turn 2. A short straight leads into Turn 3, a sharp 90-degree left-hand city block corner. Turns 4 and 5 form Silverstone, a two-apex right-hand combination that is almost a carbon copy of the Club Turn from Silverstone in the UK. Just after the exit of Turn 5, the quick left-hand Turn 6 deposits cars onto the level back straight.
Turn 7 is where the fun starts. Turns 7 through 9 are known as the Carousels, and are among the most iconic turns on the circuit, along with the Downhill and the Bridge/Loop combo. The turn, a quick, shallow right-hand bend, begins climbing a hill toward the long left-hand carousel of Turn 8. The turn is banked at a considerable degree all the way through while still ascending, and it leads directly into Turn 9, a complementary right-hand carousel at the top of the incline. Turn 9 has dual banking, with the bottom lane steeper than the outer lane. This is a very tricky part of the course, and it encourages hitting all your marks in both the Carousels exactly in order to avoid being shuffled back.
Turns 10 and 10a are a quick left-right twist at a slight downhill. Turn 11, another one OIR's greatest turns, is called the Downhill, and hugs the side of a large rocky outcropping in a long, steep left-hand descent.
Turns 12 and 13 are a right-left combination that stop the descent and begin the ascent again. Turn 14, called the Roundabout, is a 180-degree right-hand carousel that summits halfway through the corner and then sends cars downhill again.
Turn 15 is a shallow right-hand correction on the way to Turn 16, a tight left-hand hairpin. At the entrance to Turn 16, the track levels out and stays that way until the end of the Bridge.
The track then goes through Turns 17 and 17a, a left-right chicane combination, and Turns 18 and 19, a right-hand box corner that signifies the beginning of the Blocks, due to their similarity to city block corners commonly found in the Streets circuits.
Turns 20 and 21 are a left-right city-block combination, followed by Turn 22, a sharp 135-degree left-hander that begins the run to the most picturesque portion of the track, the Bridge and the Loop.
The majority of the course has been run in the open plains, but as cars take a slow right-hand straightaway toward Turn 23, they enter a dense forest. Turn 23 is an awkward 90-degree right-hand apex in the middle of a long 180-degree curve.
As cars exit Turn 23, they enter the Bridge, which runs over a hidden creek and pond. The Bridge slowly curves right, heading for the most iconic and difficult portion of the track, the Loop.
The Bridge runs right into the side of a large hill, where a wide tunnel is cut. As cars enter the tunnel, the track begins climbing steeply and turning hard right through Turn 24. After almost 180 degrees of this, the track breaks into the daylight, but it continues climbing and curving right, harder and harder until they reach the apex of Turn 25 and enter the Frontstretch. In so doing, the track actually loops over itself.
The North Loop, despite the name, does not include the Loop. The track heads due west along a front
straight not included in the GP Circuit, and in fact is an extension of the straight between Turns 2 and 3 of the GP Circuit. Upon reaching the place where Turn 3 of the GP Circuit turns hard left to go for Silverstone, it also turns (right in this case) and heads for Silverstone. It stays on the same route as the GP Circuit until it reaches Turn 16 of the GP Circuit (Turn 14 of the North Loop), where it only goes through half of the hairpin before turning hard right through Turn 14a in what amounts to be a left-right chicane combination.
Turn 15, known as the Dipper, goes through a dip, curving quickly left before correcting hard right through an immense pothole. This leads back to the start-finish line.