Let's Talk Apexes & Layers (long post)

I’m working on a project “The Integrated Racer” that will include a lot of different concepts and ideas related to teaching, learning, and optimizing driving/racing skills. Two of those concepts are Layers (looking below the surface of your experiences) and Relationships (how various elements of driving interact).

My problem is that I don’t know if this stuff only makes sense to me, or if I can explain this well enough to make it useful, or if everyone already knows this stuff, so I would really appreciate any feedback (good, bad or ugly) you might be willing to share.

BTW, this stuff I’m sharing is just how I have learned to relate to driving and how things feel to me; I’m not claiming what I’m saying is correct from an engineering or physics perspective, or is correct for you. Also, I generally focus on one tire (outside front into the apex, and outside rear out of the turn) because I feel it gives me more useful information (depth and resolution of feel) than if I spread my attention over both front tiers or both rear.

Anyway, below is my first attempt at briefly (for me) explaining the idea of layers of perception for apexes:

Dictionary definitions for Apex are:

  1. The point of sharpest curvature in a path. E.g. such as that followed by a turning vehicle.
  2. The highest or culminating point. E.g. the apex of his career.
  3. The narrowed or pointed end (tip). E.g. the apex of the tongue

Layer 1 relates to definition #1, is related to vision, and it identifies a specific location and/or target… the Geometric Apex (GA) of a corner.

Layer 2 also relates to definition #1 and vision, but it represents a very subtle shift in Apex targeting. That is, we do not always ‘target’ the GA ; often times we try to optimize performance in a turn by adjusting our apex target away from the GA (e.g. hitting an early or late apex), and therefore we are targeting an Adjusted Apex (AA).

So, layers 1 & 2 are easy to understand and relate to, and are what we typically think of when talking about apexes (you use your vision/attention to locate, and drive you kart to the desired target; GA or AA).

Cool so far, but vision is not enough to get through a corner at the limit, so let’s go one layer deeper and use definition #2 “The highest point” to relate to Apexes.

Layer 3 is not related to vision; we can’t see “The highest point” of an apex. But, we can relate the “highest point” definition to something we can “feel”, like the traction level of the outside front tire at the apex. While we all tune into sensing traction instinctively, to one degree or another, I believe that any improvements made to this skill, will be reflected in a driver’s performance and confidence levels.

Ok, so for Layer 3 we are directing our attention to traction, but what part of traction? Let’s take a short detour from apex layers to talk about the relationships that influence traction:

  • Speed is energy (or maybe that’s potential energy).
  • Steering (or braking & steering) into a turn is a request for your front tires to do work.
  • That ‘request’ causes energy to move (flow) through the chassis and into the outside front tire.
  • Energy moving into the tire produces load.
  • Load allows the tire to produce traction (to do the requested work).
  • Traction causes contact patch deflection (aka slip angle) and applies force back to the kart per your original ‘request’.

BUT, energy moving through these relationships does not happen all at once; the driver’s input causes a small amount of energy to begin moving, which produces a little tire load, which produces a little traction & slip angle, which produces a little force that acts on the kart, and that causes more energy to feed into this cycle. That is why I call this cyclic relationship the Energy Cycle.

So, the energy cycle grows over time to a peak (or “highest point”), which occurs at or near the apex, and then it collapses/rebounds when there is no longer enough energy to sustain it. This ‘collapse/rebound’ happens for two reasons:

  1. It takes a lot of energy to load a tire enough to produce the amount of traction required to twist the contact patch into a large/optimum slip angle.
  2. Generally, as you travel from the turn-in point to the apex, the kart is slowing down until minimum speed (energy level) is reached at the apex. When this happens, the delicate balance between work requested from the tire and energy available to complete that work can no longer be maintained. This is a good thing, because the corner-entry energy cycle must collapse/rebound so that the kart can complete the rotation needed for the turn, which allows the exit phase of the turn to begin.
  • If you mistakenly carry too much speed/energy into the apex, the energy cycle will not collapse/rebound where you want; the slip angle on the front tire will continue increasing, and you will drift (understeer past the target apex).
  • If you don’t carry enough speed/energy into the apex, then in addition to your mid-corner speed being slow, there will also be insufficient energy in the energy cycle collapse/rebound to power the rotation phase of the turn as desired, so you guessed it… understeer.

Now that we’ve gone even deeper into the many relationships within traction (sub layers of layer 3 if you will), I must point out that you don’t have to focus on just “traction” for level 3; you could focus on whatever works best for you; energy movement, or tire load, or slip angle. You can take even more control of what you are feeling by actively changing your focus to the most relevant information (for you), as you travel from the turn-in point to the apex.

There is a lot more to talk about regarding peaking/collapsing/rebounding forces and their relationship to how the kart rotates, but that’s a deeper discussion for another time.

Layer 4 Yet another way to relate to an apex is to use definition #3 “The narrowed or pointed end”. For example, in a double-apex turn, we are essentially driving to a point between two AAs, and that point represents where we want the energy cycle to collapse/rebound, and rotation to accelerate. In this situation, our information needs and objectives are a little different than if we are driving a single apex turn, so it might be helpful to relate to it in this slightly different way.

Anyway, I don’t want this to get too long, but there is a lot more to talk about, such as: integrating feel with understanding, the work/energy balance, energy moving like a liquid, the relationships between corner entry line selection, tire load management, and rotation management, etc.

Some ways you can try practicing or applying this apex/layer information include:

  • Tune into the slip angles of your tires when you are driving on the street. Even at normal speeds (which is what I’m advocating) they are there, but they are subtle. Long sweeping turns are good for this, and you can play with changing the load on the outside front tire by adding or removing a very small amount of throttle, and observe how your ‘line’ in influenced.
  • Again, on the street, and at reasonable speeds, in sharper turns, tune into the energy flowing into the outside front tire, when it peaks, and how the rebound of the energy influences what the front end of your car/truck is doing.
  • On track during a practice day, try running three sessions: one with very (not crazy) low front tire pressures, one with very high tire pressures, and one with normal pressures. Tune into the outside front tire and try to feel what is happening (e.g. bigger feeling slip angles with the low pressures, and opposite with high pressures). Also tune into the ‘peak & rebound’ moment at/near the apex, and how that if impacting the kart.
  • Again during practice (and when you are on your own), carry a little too little speed into some turns, and feel how that impacts you kart’s ability to rotate, then do the opposite, and carry a LITTLE too much speed and notice how the desired rotation is delayed, and often the delayed rotation energy will tend to cause the kart to snap around more than desired.

Thanks if you made it this far!


I was again reflecting on how my normal driving, when done with “sensitivity”, continues to inform my driving. We’ve discussed it, but the process of feeling the drive and extrapolating what would happen were one to take it to the limit, is full of goodies, experientially. Like, to the point I was wondering if conscious driving with feel is as beneficial as sim racing.