In the post here back in July of 2015 I argued that autocrossers should almost never drive a late apex line. I was almost on to something.
Since then I’ve read Adam Brouillard (and talked about him several times and exchanged some nice emails with him.) Brouillard explains why for each standard corner and each particular car, corner geometry and set of conditions there is only one correct apex location. Not late, not early, just one correct apex which is defined as both a location and an angle.
Here is some of what I said back then:
Late-apexing is done on track for various good reasons, but the only one related to saving time is to increase exit speed off the corner by “lengthening” the straight. The increased exit speed is carried down the ensuing straight whose average speed is now increased, reducing lap time. This is the only occasion to use a late-apex: when the length of the ensuing straight is long enough to save more time than lost in the corner.
This was wrong. It doesn’t matter how long or short the straight is. It’s wrong. My only excuse is that Brouillard’s books Perfect Corner and Perfect Corner 2 hadn’t been published when I wrote it!
While “lengthening the straight” can be done, and while it does increase the “exit speed off the corner” and while this increased speed is “carried down the ensuing straight” a late apex (an apex intended to increase the exit speed and later than the correct apex) does not decrease your lap time. Never did, never will.
I will not try to explain Brouillard and the physics. I recommend you go read him. I will say this in way of explanation, however: Suppose a corner had an off-ramp just long enough so that you could accelerate down it, turn around and then race back to the exit of the corner achieving the top speed of the car at corner exit. Your corner exit speed might go from, say, 45mph to 150mph. Your average speed down the straight might increase from 90mph to 150 mph. Could taking this exit ramp ever, under any circumstances, save time?
I don’t think so either.
When we late apex this is what we’re doing, just to a smaller extent. The more we do it the more time we lose.
Here’s my rule of thumb: it rarely pays to go in the wrong direction, no matter how fast.
When you create a late-apex, you have gone in the wrong direction (continuing toward the outside of the corner when you could have been heading more directly toward the exit), taken a longer path and actually done it slowly because of the smaller radius turn you had to make to get pointed toward the exit. Brouillard’s analysis shows that the time lost can never be made up.