Q: “What exactly is the apex of a corner, and what do I do with this information?”
A: The Apex of a corner is the place where the tires on the inside of the curve you’re driving through clip past the inner edge of the track, the most inside point or area of the corner. Using the basic “the line through a corner goes from the outside edge of the track, to the inside, and back to the outside” advice, the Apex is that “inside” point or area of the cornering line. An Apex can be a point, or an area of some small distance. An Apex can be right in the middle of the corner (geometric Apex), earlier than that (early Apex), or after that (late Apex). The Apex is also sometimes called the “clipping point.”
What do you do with this information? Lots!
If you find yourself running out of track at the exit of a corner, it’s likely that your Apex was too early; if you find yourself with lots of room when exiting a corner, your Apex was probably too late. If your Apex was too early, then next lap turn in slightly later, arcing around to a later Apex and see how that impacts your exit. If your Apex seemed too late because you didn’t need all the track as you exited the corner, turn in slightly earlier next lap. You can see how the Turn-in point, the Apex, and how you track out as you exit the corner are related; the Apex is kinda like the key pivot point, with the Turn-in and Track-out points setting up and a result of your Apex.
Of course, there are other things that can lead to you having too little or too much room at the exit of a corner (such as either not applying the throttle soon enough, or too soon), but from a “line” perspective, the Apex – where it is in the corner, and the angle your car is at when passing it – is going to dictate much of what happens after it.
With these guidelines in mind, you can use where you clip the Apex of a corner to help you figure out the line through a corner.
Oh, and there’s nothing like starting a “bench racing” session (a conversation amongst drivers – often in the paddock at the end of the day – where some bragging comes into play) with the question, “Where do you apex Turn 3?” Get ready for lots of advice for where the Apex is… and some of it might actually be worth listening to! J