Racing Line - Apex Entry and Exit

Apex Entry and Exit

In order to maintain optimal line, a race car driver will position the vehicle on track toward the outside edge of the corner before entering the corner, and turn into the corner intending to follow the path he/she plans to take through the apex. Depending on timing and speed of turn in, as well as steering input, the driver attempts to guide the vehicle through the chosen apex, often on the innermost edge of the corner. After hitting the apex, and upon exit of the corner, the driver lets the vehicle move back to the outside edge of the track, allowing the car to follow the widest, straightest path through the corner.

The entry and exit affects the speed into and out of the corner onto the following straight. A late apex is used to maximize the acceleration onto the following straight. In contrast, an early apex maximizes the use of speed from the incoming straight; this is used when approaching a corner where the following straight is a lot shorter than the straight before the corner. Hitting the apex in the middle is a reasonable way to take a corner, keeping a good speed constant into and out of the corner, and maximizing mid-corner minimum speed.

For example, a sector of the track is a 1/4 mile straight leading up to a 90 degree corner that leads onto a 100m straight that then turns into a hairpin that follows onto a long straight. The straight is where the car would have its optimum speed and it is leading into a sharp 90 degree corner, the early apex into the corner would be used to make as much use of the incoming speed as possible. Acceleration onto the following straight would be delayed, reducing top speed on the straight leading to the hairpin. Because the car will be at a lower speed towards the hairpin, minimum braking can be used, with a late apex to allow early acceleration and maximum speed onto the following straight. This would be the quickest way to take this sector of the track, maximizing the speed down the longer straights.

Depending upon cornering situations, techniques like trail braking can be used to maintain more speed upon entry of a corner, and attaining more grip while turning into the corner, and has an effect on apex selection. In this technique, brake pressure is applied slightly later than usual upon deceleration, and is maintained during steering input, sometimes all the way to the apex. The action of braking causes a weight transfer in the vehicle, shifting more weight from the rear of the car forward to the front tires, increasing the normal force on them and in turn increasing the amount of traction the front (steering) wheels have. Because of the characteristics of weight transfer, this technique causes weight to be shifted away from the rear of the car, resulting in lower rear traction, and can be used to induce oversteer in some cases.

Early apex is employed to block inside overtaking in racing.