Read your Car

"How do I know when my tires are at their limit, I’m driving my car as fast as it can go, and what handling problems my car has?” Aren’t those the 64 million dollar questions?

I’ve spent a lot of time focused on defining what “driving at the limit” is, how we as drivers sense it, what we can do to improve our ability to sense the limit, and how we can use this information to better read how our car is handling (and ultimately, how we can use that information to tune the car’s handling).

During the Reading Your Car webinar (you can download a recording by clicking here and scrolling to that specific webinar) I defined a new phrase describing the bits of feedback we take in through our senses that help us “read” the limits of the car/tires. I call them “limit sensors.”

So, what are the “limit sensors”?

·        Vibrations through the steering wheel

·        The "weight" of the steering

·        “Push back” through the steering (typically referred to as feedback through the wheel)

·        The amount of g-loads pushing against our body, and whether they are increasing, decreasing and staying constant

·        Any change in the weight transfer, either pitching, squatting or rolling of the chassis

·        A change in balance of our body, and therefore the car

·        Change in yaw or rotation of the car

·        The sound coming from the tires

·        A change in the wind noise passing the car indicating a change in velocity of the car

·        An acceleration in the change of visual picture (the horizon is scanning past your view more quickly than before), or deceleration

·        A difference between where we expect the car to be pointing and where it's actually pointing

Each of these provide clues and cues as to when our car is at its limit, and when it’s not. So, let’s talk a little more about some of these “limit sensors.”

First, it’s interesting that we’re often told that our vision is the most important sense we rely on when driving, and yet most of the limit sensors I listed above are related to our kinesthetic sense. I do believe vision is the most important sense we rely on to get around the track, but kinesthetic and auditory are more important when it comes to sensing the limits.

We sense the angle the car is pointing, or yaw (technically it’s “body slip angle,” but for our purposes, yaw will do). If we're driving near the limit, the car will not point exactly where you've steered it. With experience and practice, we calibrate our steering movement to the reaction of the car. If it doesn't go where you think you've turned to, it's understeering. If it turned more than you wanted, it's oversteer. When our mind compares that oversteer to understeer, it calculates whether the tires are at their limit or not.

Taking this to an extreme, first imagine the front tires slipping more than the rears – understeer. You’ve turned the steering enough to make the car go through a corner on an arc you want, but because the fronts are slipping, the car points at an angle less than you intended. It’s not pointing into the corner as much as you’d like. The cells in your brain recognize this and says, “Aha! Understeer! The front tires are slightly beyond their limit.”

You get to the next corner, turn in on the arc you want, and the car rotates, or turns more than you expected. It’s oversteering, as the rear tires are slipping more than the fronts. Once again, comparing expected to real yaw angle, balance, g-forces, feedback through the steering wheel, sound of the tires, and the change in visual picture, your brain interprets this and says, “Ahh! Oversteer! The rear tires are slightly beyond their limit.”

Now, you get to the next corner, a long, sweeping right-hander. You turn in and the car begins tracking exactly as you expected, on an arc or line you intended and expected. But a fraction of a second later your brain realizes that the arc is increasing – the radius is getting bigger. The steering feels different from two corners ago when you had understeer, and from the previous corner where the car turned more than you wanted, with oversteer. It’s a bit of both. Initially, as you turned into the corner you felt the g-forces build up, but now you notice them beginning to decrease, just slightly. It’s subtle, but noticeable. Essentially, all four tires are slipping equally. As your brain cries out (in a happy way!), “Yes! We’re at the limit… maybe even just slightly beyond,” you begin making adjustments to ensure you follow a line close enough to what you intended so as not to drive off the track. Depending on what you’re doing at this very instant, you may turn the steering wheel just a little bit more, or unwind it slightly; you may release the brakes quicker or slower; you may delay squeezing back on the throttle, apply it a little more, or ease off it a little. Any of these reactions are intended to manage the amount of slip you allow the tires to continue with, and the direction the car is traveling.

Notice that we compare the amount of steering, and where we expect the car to go with the actual direction the car is going. Go through a corner at medium speed and quickly - almost violently - turn the steering wheel until you feel understeer. This is extreme understeer, but it gives you some sense of what it feels like. Does the steering feel heavier or lighter? Depending on your tires and the geometry of your front suspension - caster, pneumatic trail, and so on - you may notice an increase or decrease in steering "weight."

Be aware of how much you turn the steering wheel. Too much and it's understeering. Too little and it's oversteering.

As the front tires distort when near the limit, the tread/carcass of the tire vibrates. That's something we feel as a vibration or feel back through the steering wheel. Remember, the steering wheel is both an input (make the car turn) and output (what do I sense) device. The amount of vibration feedback we get through the wheel helps us determine whether the front tires are at their limit.

Your brain is extremely programmable. If you spend enough time with the tires at their limit while you consciously pay attention to these, you will calibrate all of these pieces of feedback and eventually get to where you subconsciously sense the limits of the tires and car.

 

Many people believe that sensing the limit of the car is something that a rare few were born with. I'm not going to argue that point, but what I know as fact is that this is something that most (if not all) drivers develop. It’s a learnable skill. That's why a driver improves with experience. Now, some drivers seem to learn this skill quicker than others, and that's a good argument for the possibility of them being born with something special. But could it also be something they developed through other activities as a kid. For example, riding bicycles, skateboarding, skiing, or anything else that requires balance and the ability to notice subtle visual differences in direction and forces acting against the body?

This is why skid pad training is so effective. At a low speed, all of these pieces of feedback are going into the brain, being catalogued and calibrated to past experiences, and lasting long enough that the driver can actually focus on them. On the track, a "moment" of understeer or oversteer may last a fraction of a second - such a short amount of time that you don't actually recognize it. But on a skid pad, that slide may last many seconds, giving your brain lots of time to process it. Then, when at speed on track, your brain recognizes the minute amounts of under/oversteer and is therefore more sensitive to it.

Steering effort is a signal. Imagine you enter a corner and the rear begins to step out, oversteering. At first, there is a certain amount of steering effort required to get the car to change direction - let's say that is 100 units of effort. As the car begins to oversteer, the car doesn't need as much steering to get it to rotate and point into the corner, therefore it requires less steering, and less steering effort - let's say 75 units of effort. Right there, you sense the car has begun to oversteer.

What about understeer? You turn in using 100 units of steering effort, but the car does not change direction as much as you'd like - it's understeering. No matter who you are, at least initially you will turn the steering wheel more - it's instinctual to do so (despite it being the wrong thing to do). With the front tires now at a more extreme angle to the track, the steering effort will rise - let's say to 125 units. If you turn the wheel more (again, not the right thing to do), eventually you go "over the top" and the tires will begin to slide even more and the steering effort will drop, to say 90 units of effort. If you do the right thing to manage understeer and reduce the steering angle slightly, again the steering effort will drop - let's say back to 100, as you've brought the angle back to the point where the tire is working within it's ideal slip angle range. This increase, followed by a decrease is an indication to the brain that you're experiencing understeer. Do this enough times and you'll become super-sensitive to it, recognizing and reacting to it instantly.

Understand that we're not only sensing how much of a change in tire grip and yaw, but also the rate of change. It’s impossible to drive through a corner anywhere near “fast” without causing some amount of yaw as the tires slip to different degrees, front to rear. It’s how quickly the car yaws that is important, and when we deliberately pay attention to this, we become more sensitive to the limits.

Now, something so obvious and basic that you may not have really paid enough attention to it. To sense your car’s limit, your seat needs to support you. If the car yaws, but you don’t as much because you’re moving around in the seat, you won’t have as much feel for the limit. You need to move with the car.

You also need “light hands” on the steering wheel. If you’re driving with a death grip on the wheel, you’ll take in less feedback through the steering, up through your hands and arms, and ultimately to your brain. A lighter touch on the wheel will provide more feedback.

Also consider what you do with your head. If you lean your head, not only does your visual picture change, but your sense of balance is not in tune with your car. Keep your head upright.

Remember, humans are adaptable. I recently drove a Porsche 944 and the steering was not as responsive as the car I had just hopped out of. As I turned into the first corner I realized I needed to turn the wheel much more. It even took me by surprise. By the second corner it was no longer a surprise, and by the third and fourth turns I was expecting a less responsive reaction to my turning of the wheel. Within a lap or two I adapted, and it felt normal. When I then got behind the wheel of the first car – the one with responsive steering – of course I noticed the difference. But because the differences between the two cars were fresh in my mind, it didn’t take a lap or two to adapt. By the end of the first corner I was in tune with the car. We adapt, especially if we give our minds the specific information it’s looking for. In other words, if we deliberately pay attention to what we see, feel and hear.

Having said all that, if the car is not telling you what it needs, then you're not driving near the limit. Period. If it doesn’t give you any of the feedback that I’ve written about here, then you know the car can be driven faster. As I say, “Make the car show its weakness.” If you don’t feel a weakness, you know you’re not at the limit. Every car has a “weakness” – something that shows up when you’re driving at the limit.

Finally, even though you may be driving your car at its limit, with the tires are their very edge of traction where even half a mile per hour more would have them sliding more and beginning to lose grip, you may not be driving your car as fast as it can go. What?! Yes, you may have created an artificially low limit for your tires by not balancing your car in the ideal (for that very instant’s situation) way. But that’s a topic of another day.