Check Your Understeer At The Door...

Updated: Jul 23, 2021

If there’s a common refrain from “newbie” track drivers, says Adrian Burford, it is that their car understeers.

And that’s not just from drivers of powerful front-wheel-drive hatches – it is from everything. I’ve said it before – if you don’t set up the car to point at the apex (and then hit it), you’ll never exit the corner under maximum power and thus maintain the highest possible average speed for the length of the following straight.

The worst kind of understeer is the kind where you’re forced to get out of the throttle post-apex because the nose is running off the road. Then all you can do is wait for the lateral grip to come back, which eventually allows you to reapply power with the tyres’ trajectory now heading along rather than across the tarmac. Unfortunately, the fact that you’re still using a chunk of the grip to control the lateral forces way after the apex suggests you got it wrong at the start of the turning phase.

There are plenty of signals to identify this with a VBOX datalogger but you can also see it clearly spectating from the inside of the turn. It’ll be the car that is still leaning when the corner is long gone, because the driver has turned it into a never-ending arc, rather than executing the majority of the turn earlier. Achieving this is crucial because an earlier, decisive steering input will also mean at a lower speed, when the tyres will react more willingly to a change of dynamic state.

The other way of spotting the understeer is to try to look at the driver: he’ll be the one still wrestling with the wheel when hands should be back at the 10 and 2 position.

You’d think driver-induced oversteer would be more common. Not necessarily. That’s partly because so much of the road car market is now FWD. Stability control systems have also done much to quell unruly RWD oversteer and most control systems won’t let you add power if there’s excessive steering lock applied – or if it isn’t being simultaneously reduced as throttle angle increases.

To be clear: we aren’t talking about cars that have handling issues. We’re talking about driver technique issues. There are patterns here. This kind of understeer is definitely most apparent when drivers are consciously trying to “be fast”. They’re trying too hard.

I often use a golfing analogy when trying to explain this. I haven’t hit a white ball for decades but I recall often being at my best (a relative term) when I’d gone out there without too many expectations and merely planned on just smacking a few balls about.

Unfortunately, after making decent work of the first few holes, expectation reared its ugly head and that’s when things went wrong. Overthinking it is a great reminder why Golf is such a mental game. Driving fast can be the same.

Once again, I’m going to use what we do at the AMG Academy as an example. Those tentative early sessions are usually quite predictable, and we see the speed build. Then the driver starts trying to race. They consciously hurry the process and it usually manifests in arriving at a turn too fast (having not braked decisively enough and/or at the right point).

Turning in while still braking is a sure-fire way of overloading the outside front tyre and it doesn’t take much to end up beyond its total grip envelope, even momentarily. Momentarily is enough, and that’s when the understeer starts, shifting the nose outward by a foot or two, while any chance of hitting the apex goes abegging. So now you must wait for the fronts to recover, and then coax the nose back in again.

This phase is clearly visible on a VBOX speed trace – there’s a flat line, often until way past the apex. The speed curve ends up being shaped like an L and not like a V – which is the signature letter you should get if you bring the speed down to the correct level, unsqueeze the brake, turn in, and start accelerating again almost immediately. Remembering, of course, that the throttle is an analogue instrument and not binary – good drivers use the whole spectrum of the loud pedal, from 1 to 100 percent and everything inbetween.

Simply going in too fast has a similar result and normally needs great armfuls of lock and the use of lateral G to reduce longitudinal G (if you get my drift) before going anywhere near the right hand pedal. It is remarkable what going in just four or five km/h too fast at Zwartkops’ hairpin does – it is enough to push the tyre over the limit and make the fronts ”blur” sideways.

The longitudinal G trace is a great tool for reinforcing all this when back in the “lab” after the session. Just where and when does that signal go into positive territory after braking and turning? And does it stay positive? And does the positive value increase steadily?

Looking at laps driven by Academy Top Gun, Clint Weston, this tends to happen sooner rather than later and when overlaying teacher and student at the slower corners (Turn Eight onto the pit straight is also good for illustrating this) there is invariably a Eureka moment. When we also have a throttle position graph available, it is another useful way of conveying the same message, and not only about where the throttle is first applied but also the rate of application.

Of course, knowing what you’re doing wrong isn’t a guarantee that you’ll magically fix it from the next session, but it’s a start. Patience is a virtue, especially exiting slow corners. It is another reason why the calm, progressive guys are also invariably the fast guys – and the slow guys keep blaming the understeer on the machinery.

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