Q: “I am struggling with one specific aspect with my racing car. That is mid-corner (largest steering, no brake or throttle) understeer. Not only does this lead to exit oversteer, but also it seems I can’t influence it or dial it out with trail braking in the corner entry. No matter how late I stay on the brakes, the car’s behavior doesn’t change and it just understeers. Is this only fixed by car setup changes?”
A: My first thought is to be sure about what you are doing when the understeer begins, and continues. You say you’re not on the brakes or throttle, so okay, that suggests that you’re not overloading the front tires with too much trail braking, nor are you unloading the fronts by accelerating too aggressively. But the fact that it leads to oversteer makes me think about your steering.
What are you doing with the steering wheel when the understeer begins, and then when it continues? Many, and possibly most, drivers turn the steering wheel more when they have understeer. Why? Because it’s human instinct to turn the wheel more if the car is not following the arc through the corner that you want.
If you do turn the wheel more when you have understeer – and even if you don’t turn it more, but you keep the same amount of steering input – think about what’s happening with the front tires: they’re at an angle where they can’t grip the track surface, and then you put even more steering angle in. At this point they begin to scrub off some speed until your car is slowed down enough where the steering angle is not excessive (for that speed), they grip the track and begin to turn the car more, and suddenly you find the car turning more than you wanted – it’s oversteering.
Amongst race engineers, this is referred to as the “understeer-snap-oversteer” issue, and nine times out of ten it’s because the driver turned the steering more when they really should have straightened it very slightly, back to angle where the front tires can grip the track.
So, the first thing you should think about and be aware of when you have this understeer is whether you’re straightening the steering just a slight amount. If not, that’s how you cure the problem.
Later in your question you mention that no matter how late you stay on the brakes, you can’t get the car to turn – it just understeers. Keep in mind that trail braking more can help reduce understeer by keeping load on the front tires, but it can also increase the understeer because you’re asking too much of the front tires. So, at some point, try reducing the amount of trail braking to see if it reduces the understeer.
Finally, yes there comes a time when the only way to fix understeer is through changes to your car’s setup. Of course, how you actually do that is a huge topic, and you can download a free eBook I wrote on the subject, How to Tune Your Car’s Handling: A Driver’s Guide by clicking here.