What makes a car fun to drive?

What makes a car fun to drive? It can probably be summed up in two phrases: it gives you confidence, and doesn’t feel like it is trying to kill you.

A good analogy is riding horses. A fun horse will be a bit racy and will like to put the hammer down, but there is a sense that it is looking after you.

Contrast that with an old nag. As soon as it unwillingly starts galloping it tries to chuck you off, and has a penchant for skimming trees without leaving room for your knees.

The difference between a trusty steed and an old nag gets even more evident with cars, and the speeds they travel. It’s one of those things that is obvious when it’s missing, but difficult to spot at first glance.

Until you have experienced chaos it is hard to understand. Like the first time you live with a messy housemate after moving out of home, or experience a rear-engined car at high speed with the wrong aero balance, you can’t fully grasp the power of the self-reinforcing forces you are dealing with.

Having engaged with and become aware of chaos, the rules of household cleanliness, or laws of physics, become etched in your mind – and you become reluctant to ever get on the wrong side of them again…

Testing prototype McLaren models taught me a lot about cars wanting to kill me. I remember one instance while testing at a test track called Nardo.

Nadro is in Puglia, in Italy’s south. The region is famous for its sparkling coastlines, mafia and amazing seafood pastas as well as the incredible Porsche-owned proving ground. There, nestled inside a 12.5km high-speed ring (visible from space) is one of the coolest racetracks ever concocted.

We were testing an early-stage McLaren 720S prototype and the air brake (or rear wing) wasn’t the most reliable, and worse, it didn’t warn you when it had stopped working. And this time it did stop working…

If you have ever towed a trailer without enough weight on the draw bar you will know what I mean.

Going from a 40/60 per cent to a 120/-20% aero balance in the blink of an eye is not a fun thing to do at high speed. The guy sitting next to me had raced Carrera Cup and Formula Renault and still involuntarily grunted as we snapped sideways over a crest.

Thankfully my days rallying Holden Geminis must have taught me something and we avoided disaster.

Very scary things can happen at high speed yet you still feel like the car was trying to help you.

I was once testing a Radical SR3 sports car at Spa in Belgium. The problem with windscreen-less open-top aero cars is you never know when it has started raining. The aero sweeps the drops of water over the car without leaving any evidence on your helmet visor.

Running on slick tyres and holding it flat through Eau Rouge quickly turned the Eau into “Ohhh”, and the Rouge into “Good Heavens”. The car snapped sideways at 210km/h.

This time, the car was communicating its intentions clearly. I could feel the weight in the steering saying that it was starting to lose grip, but that lifting off the throttle right then would make things worse.

Moments later I sensed that the rear-end would hold if I jammed on as much steering correction as I could muster then lifted off…

The car then telegraphed to me that it was about to snap back the other way and told me that if I jammed the steering wheel as hard as I could in the other direction I had a pretty good chance of making it.

Just like that I’d survived a heart-stopping moment and could head to the pits with my tail between my legs for a set of wet tyres.

The difference was in the way the car communicated. It was behaving as it should and it was as forgiving as it could be while things were up in the air. [Ed: don’t try this – going flat-out through Eau Rouge – at home]

Like social skills, how and why a car inspires confidence is a harder thing to nail down. I like to equate it to communication. A car that inspires confidence is an active listener.

In an effort to become a better boyfriend I once read an article on active listening. Apparently, if your girlfriend tells you something and you repeat back to her a summary of what she has just said and how it made her feel, you will avoid fights. [Ed: don’t try this at home either!!!]

Fights are like snap oversteer at 200km/h on a wet track you thought was dry. Always exciting but never fun. The white-knuckle conflict resolution when the car wants to snap back the other way on an overcorrection doesn’t do much for your confidence either.

Confidence in part is down to overshoot. When you turn into a corner, the car momentarily turns in a bit more than you asked, then settles into just the right amount.

It’s like active listening. You tell the car that you would like to turn into a corner and that if we did it would be great. The car says, “Yes, let’s turn into the corner, and to show you I’m listening, I’m going to turn in a little more than you asked just for a fraction of a second before settling into the corner.”

In the immortal words of Take That: “You'll be right and understood.”

Obviously too much of a good thing is bad and too much overshoot is no exception. Take That best summed this up in the line: “In the twist of separation you excelled at being free.”

Like all things chassis-related, overshoot is an amalgamation of a lot of things. Things like tyre sidewall stiffness and damping are key ingredients, but there are lots of other factors.

As you’ve gathered by now, with the level of complexity involved it comes down to trial and error.

Once you’ve found the sweet spot, small changes have big effects. You might change the construction of a tyre (for example, the belt angle by two degrees) and get the perfect overshoot, but in the process lose some steering directness.

You might add a 0.2mm-thick shim on the compression side of the rear dampers and all of a sudden the car feels compact, connected and with the perfect overshoot.

To measure overshoot, chassis engineers do a manoeuvre called a step steer. They drive along at a constant speed then, like a step change on an oscilloscope, they quickly turn the steering wheel to a set angle and hold it there.

From there it’s time to look at the data and more specifically the squiggly lines.

They plot the steering angle (which is the input) against the yaw angle and lateral acceleration.

Yaw angle is a measure of how quickly the car is turning, and lateral acceleration is what you feel pushing you into the centre of the car or out the door depending on which you just turned (to avoid offending Sir Isaac Newton, it’s the mass multiplied by the acceleration).

The overshoot is where the squiggly lines of the yaw and the lateral acceleration rise above the step top of the steering angle line. If you compare the lines like for like (normalised) you can measure the overshoot as a percentage.

How a car reacts to a step steer tells us other interesting things that pertain to confidence.

Response time is how quickly you answer during active listening. McLaren supercars answer the request from the steering wheel quickly and Toyota Troopies answer it slowly.

To measure response time, the start is when the steering angle crosses 10 per cent of its final value and finishes when the yaw reaches 90 per cent of its final value.

Settling time is the time it takes the car to settle into the corner after the initial step input.

Step inputs always induce oscillations, more commonly known as wobbles, and excessive wobbling is never nice. The problem with wobbling (or said differently, not being settled) is when you need to quickly readjust course mid-wobble.

In that scenario, you can easily catch the car napping, or worse, it will overreact.

Rally drivers have perfected the art of gauging response times, overshoot and settling time to spectacular effect with Scandinavian Flicks. They trigger yaw with a sharp turn in the direction they don’t want to go, then wait for the exact moment that the car is bouncing back in the direction they do before turning-in.

I guess that sums up driving confidence; a freedom to do what you believe to be possible. And a confidence-inspiring car is one which follows as best it can within the laws of physics.

Confidence is one of those virtuous or vicious cycles. A great car works with you to build up your confidence.

You start by doing something a little bit outside your comfort zone and the car does it with ease. A feedback loop starts where you keep building, always a little outside your comfort zone.

The key is not to go too far outside your comfort zone, where you will get bitten so hard you will never try again – like a beginner skier who accidentally ends up halfway down on a red run with no way back.

On the flipside, you can’t stay in your comfort zone either – the equivalent of never leaving the café at the bottom of the ski slopes.