Q: “There is one thing that I have wanted to know, but I never found anyone whom I thought would be able to answer my question correctly – until now. How do you save tires? How do you abuse tires on the track? Oops, that’s two questions. The second question may seem obvious, but drivers do many things with their cars that we are not aware of, or assume to be the right thing to do.”
A: That’s tough one to describe – it’s one of those things that’s tough to put into words, but you know when you experience it! Here’s an example of something that I experienced just recently.
I recently drove in a World Racing League event – an 8-hour race on Saturday, and another 8-hour on Sunday – at COTA. As you know, COTA has that long carousel corner, turns 16-18. I was driving a 2016 BMW M240i, and the series mandates DOT tires (we were on some model of Goodyear tire). During the one practice session I had in the car on Friday, I identified the single biggest handling issue as being understeer in this section of track. As it’s a long corner – almost 180 degrees and taken at about 85-90 MPH – any amount of understeer was going to beat up the tires for a long time (almost 10 seconds in the BMW through the entire corner). If I pushed the car harder to carry just another MPH or two, the understeer would get worse – I’d feel the front tires “grinding” (sliding/scrubbing too much), and I’d want to turn the steering wheel more. But, as you know, turning the steering wheel more does not fix understeer. In fact, it can make it worse – but it is a natural response by most drivers. To answer your second question first, this was abusing the tires.
I recognized the feel and sound of the scrubbing/grinding left front tire, and knew that if we did that for 8 hours, it wouldn’t last. So, to try to save that tire, I had to “relax” the steering (turn it less), and avoid the scrubbing/grinding of the front left tire. And this is important – I could hear it. There was a dramatic difference in sound between the scrubbing/grinding tire, and the tire when it was at its limit (and when it was below the limit, almost making no noise at all). So, part of my read on whether I was abusing the tires, keeping them right at the limit, and saving them by being just below the limit was an auditory thing. It was also a kinesthetic thing – I could feel the difference through the steering. The steering is not just an input device (we turn it to change direction), but it’s an output device (we get feedback from it). As I increased speed the radius my car was following increased, due to the understeer – I could feel that the car was not following the path I wanted, so it was understeering. It was not responding to the steering input as much as desired. If I tested the grip level by turning the steering a bit more into the turn, it would only slide more, the tires would howl/growl/complain more, and I knew that I was increasing the amount of understeer – that would be abusing the tires. So, again, I “relaxed” the steering and managed the throttle so I wasn’t increasing speed – the speed lowered a MPH or so, and got to a speed where the understeer was lessened, and almost non-existent. I managed the understeer, and therefore saved the tires.
Ultimately, we changed the car’s setup to make the car more balanced in that corner, reducing the amount of understeer. So, beyond lessening the steering angle and speed slightly, the other way I saved the tires was to change the car’s setup to reduce the understeer.
The same kind of thing can happen with the rear tires, primarily exiting the corner and controlling/managing power-down oversteer (assuming a rear drive car). If I feel and hear the rear tires sliding too much, I’m going to be a bit more gentle applying the throttle to avoid wheelspin or oversteer.
Obviously, the first step in saving tires is identifying when it’s needed. Then it’s a matter of managing steering angle, throttle input, and speed to keep the tires below that point where the tires are being abused. A driver might have to do some of this in the brake zones, too, if the tires are really being abused, or you really have to save them. That’s simply braking slightly earlier and lighter.