The turn-in point is crucial because it affects the racing line and therefore important to allow the driver to carry the most speed through the corner. By choosing the correct turn-in point, the driver can set themselves up for the best possible exit speed from the corner. So how do you determine the best possible turn in point? This comes from a mixture of track knowledge and experience but there are some basic rules to help you understand as a starting base for you to experiment from.

Early Apex: Choosing an early apex means you aim to reach the innermost point of the corner earlier in the turn. This approach can have a few advantages:

• Tighter Line: By taking a tighter line, you can potentially reduce the overall distance traveled through the corner, allowing for a shorter path.
• Early Exit: With an early apex, you can start unwinding the steering wheel sooner and accelerate earlier, enabling you to achieve a higher exit speed out of the corner.

However, an early apex also has some potential drawbacks:

• Limited Visibility: By hugging the inside of the corner early, your line of sight around the corner may be restricted, making it harder to anticipate potential hazards or oncoming traffic.
• Increased Risk of Understeer: If you carry too much speed into the corner and reach the apex too early, you might experience understeer (the front tires losing grip), which can lead to a loss of control.

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Late Apex: Opting for a late apex means delaying your turn-in and aiming to reach the innermost point of the corner later in the turn. This approach offers a few benefits:

• Better Visibility: By delaying your turn-in, you can maintain a wider line of sight throughout the corner, improving your ability to anticipate any obstacles or traffic.
• Safer Entry: With a late apex, you have the opportunity to brake later and carry more speed into the corner without the risk of understeer.
• Smooth Exit: By delaying your turn-in, you can set up for a smoother and more controlled exit, gradually applying power as you unwind the steering wheel.

However, there are potential downsides to a late apex:

• Longer Path: Taking a wider line and delaying the apex means covering a greater distance through the corner, potentially resulting in a slightly slower overall speed.
• Delayed Acceleration: Since the exit is delayed compared to an early apex, you may have to wait longer before applying full throttle, this isn't always the case.
• Slower / tighter radius at turn in: As you will be turning in later the initial steer angle will be steeper, greater steering angle means slower cornering however there a compromise that your chance to straighten the car and accelerate soon can be improved.
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If you opt for an early apex, your turn-in point will be earlier, closer to the corner's entry. Conversely, if you choose a late apex, your turn-in point will be later, closer to the midpoint of the corner. Adjusting the turn-in point allows you to position your vehicle accordingly to hit the desired apex.

With all this information, you can see that there are many factors to consider. Also, it is very important to understand that the corners are not all separate entities, they are are joined and relate the straight before and the straight after. Not to mention complex corners where one corner flows into the next.

The the general rule is the tighter the corner the later the apex you can take in order to ensure you have a good fast exit out of the corner, the shallower the corner the more you'll be able to take the geometrical line which should be the fastest line through the corner and this is closer to an early or mid point apex.

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On the diagram on the left you'll see that a late turn in of the reference "blue" line at the beginning of the corner then allows, if the car has turned enough to be able to get your foot down earlier and faster on the exit from the corner. In the right hand diagram on a faster corner, it is possible to maintain your speed through the corner better so an earlier apex is fine, power on and plough through the corner. The tyres are more capable of maintain traction as there is less of a corner radius thus less lateral g-forces to contend with.