The Endless Cycle of Improvement

Mike McGinnis

Modifying vehicles can be a lifelong addiction for many reasons, one of which is the endless possibility for improvement; improvement of your vehicle(s), your skills, and knowledge. Modern vehicles are sufficiently complex that you can spend a lifetime working towards optimization of one aspect of performance. Fortunately for most of us, you can also make meaningful advances with just a bit of time and knowledge.

But what does a deeper dive look like? Let’s look at a question that seems pretty straight forward on the surface: How much camber should my car have? Some are content with what’s in their vehicle owner’s manual, some tinker a little, but there are others who have spent hundreds of hours on the subject. In this example I’ll stick to thoughts on camber for circuit use on a dry day to “simplify things”, which as you’ll see only shrinks this from a gigantic question to a huge one.

What lies below are options, considerations, and hopefully motivation to question some aspect of vehicle setup.

Here are some of the ways I’ve seen people make camber determinations:
  1. Even temp across the tire
  2. Specific spread i.e. 20 F hotter inside third vs. outside third
  3. Scrape tires then read graining across them
  4. Even wear inside to outside
  5. Specific wear gradient inside to outside
  6. Positive driver feedback turn in
  7. Positive driver feedback mid corner grip
  8. Peak or average lateral G values through corners
  9. Match camber of the track
  10. Cheated asymmetrically based on high percentage of corners being in the same direction i.e. Lime Rock Park.
  11. To achieve desired contact patch during cornering based on the amount of caster (for front)
  12. To achieve desired contact patch during squat under power (for rear)
  13. Based on vehicle weight, tire size
13 options already and those came easy. If I only start down the road of thinking about option 1, here’s a list of what that stream of consciousness looks like:
  • What were the tire temperatures when the car went out on track?
  • Over the course of a lap what’s putting heat into the tires?
  • Of the total contributors, how much do ambient factors like track temp and mu, air temp, and cloud cover matter vs. vehicle driving behavior?
  • How much of the heat is being introduced by braking vs. acceleration vs. cornering?
  • There’s heat from the brake system convecting in the wheelhouse and there’s heat conducting from pad to caliper to knuckle to hub to wheel to tire. How much impact does one have vs. the other and do I want to mitigate either somehow?
  • Depending on wheel design and offset the spokes could contact the barrel near the inside, middle, or outside of the tire. How significant or not is this?
  • How do tire construction and materials impact heat transfer from wheel to tire?
  • What happens to tire temperature spread over 1 lap vs. 3 vs. 10?
  • What does the mathematical relationship of tire temperature to longitudinal/lateral G or vehicle weight look like?
  • How much do individual driver errors i.e. inducing push or excess wheel spin alter momentary and end of session temperatures?
  • What tread temperature offers best mu, what carcass temperature offers the best performance? How far apart are those two temperatures?
  • Does increased temperature cause me to hit a tire pressure past which localized tread surface temperature increases exponentially based on contact patch reduction?
  • In order to make temps even across the tire, wouldn’t you have to ride on the outside of the tire through corners since you’re riding on the inside on straights?

What is temperature spread really telling me anyway?

Questions can lead to more questions than answers. This “tiny” subject of camber goes on and on and I’m barely scratching the surface. I haven’t even touched on dynamic camber due to camber gain and caster.

Any time a subject spirals out of control, I try to think about my primary goal, then build the questions back out from there.

Adjusting tire temperature, camber, alignment may help me achieve my goal, but they’re not the end game. At the end of the day the goal is simple. I want to run the quickest lap I can with the car and tires I have. How can camber adjustment get me there?

As I review data, I can see strengths and weaknesses of different vehicles and setups on a given track. If I’m adjusting camber I’m looking for more grip, but in what segments of the track? If acceleration is decent once the car is straight, but braking, and corner entry/mid/exit grip are all poor what direction should I go? Braking grip seems poor from excessive front camber, but will reducing front camber detract from turn in performance? The questions are coming back…

In order to make better sense of things, I like to increase data and reduce variables. Sounds easy right? Not so much…how do I increase data? Here’s a few ideas for the camber example:
  1. Consult the tire and vehicle manufacturers. Consulting either only works if they have meaningful data to provide.
  2. Record ambient data, lap times, tire temps post session. This doesn’t require anything fancy, and it’s a start.
  3. Record driving impressions and attempt correlation with data and camber setting.
  4. Add vehicle sensors and logging. Tire temperature and pressure sensors, G sensor, braking force, wheel slip, ride height monitors, etc. It’s only money right?
How do I reduce variables?
  1. Record as much data as possible.
  2. As best I can, control conditions to make them repeatable. Drive in similar fashion, don’t alter the vehicle between tests, use the same track, same tires (but replace them if their performance degrades significantly), etc.
Am I ready to start this investigation?

Not quite. My GTR currently has excessive tire pressure rise, static alignment shifting due to some components requiring better methods of restraint, and alignment inconsistency on track due to bushing slop. I can’t reasonably develop optimized camber settings until I can resolve or better manage these variables. I have plans to reduce the second 2 concerns by upgrading some bushings and using Loctite, performing more frequent nut and bolt checks. If those improvements stabilize alignment, maybe I’ll have more grip and reduce the rate at which tire pressure rises, but that remains to be seen. Even if I can’t control the pressure rise, I can control the pressure I go on track, and I can control how I drive, and for how long. With these concerns behind me, I’ll be ready to start testing camber tuning options in earnest.

We do the best we can with the tools and knowledge we have at the time. Then we look back years later, chuckle, ask better questions, gather better data, and come to more informed conclusions.

Hopefully this got your gears turning. Think of a topic you haven’t pondered in a while, question your old results. You might just find the few tenths you’ve been looking for!