Basic knowledge - tends to be rather boring but if you want to understand the background of driving on a race track, then unfortunately this is just part of it. ;-)
Today it is all about the Traction Circle. Simply put, it's about how the lateral and longitudinal forces affect the tire and its ability to transmit grip.
Lateral = cornering
Longitudinal = braking or acceleration
If we put the brakes on when we are driving straight ahead, the tyre can put 100% of its grip into braking performance.
For example, if we drive only in a circle on a circular plate, at a constant speed, the tyre can use 100% of its grip for cornering.
As we all know, the driving conditions on a racetrack are usually a bit different: we brake into a corner and accelerate out of a bend. This means that there is always an overlap of lateral and
longitudinal forces. This overlap restricts the maximum force that can be transmitted laterally and longitudinally, because two forces act on the tire at the same time.
So when we brake into a curve, the tire must bring the braking force (longitudinal) and the lateral force (lateral) to the road. To do this, the driver must reduce the braking force as soon as he
starts to turn into the corner. Why? Well, if the tyre puts 100% of its grip on braking, then it has no reserves for cornering. By reducing the brake pressure, we also reduce the braking force
and thus we give the tyre the possibility to transfer grip from deceleration to cornering, so that e.g. we can use 75 % of the lateral and 75 % of the longitudinal grip that is available.
What applies to braking also applies to acceleration: If we would just bluntly apply full throttle in the curve, the tires would spin and we would spin. Why? The rear tyre already gives up part
of its grip for lateral support when cornering, so the grip for acceleration is limited, in the example from above we can use ~ 90 % of the lateral grip but only 50 % of the longitudinal
grip.
The more we turn into the curve, the more the brake pressure has to be reduced.
Now some of you may ask yourself: "Why do I have to reduce the brake pressure, I have ABS?" That's right, most racing cars have ABS (anti-lock-system), which is supposed to prevent tires from
locking when braking. In fact, when we talk about high performance GT3 race cars, it makes a lot of sense to work with ABS. But in production racing cars (such as in the V class of the VLN / NLS)
or road cars, the ABS works so roughly that intervention usually results in poorer braking performance. And when the ABS starts to work, you have usually already exceeded the tyre's grip limit.
Please be aware that the numbers given here are just examples - so don't nail me down on the exact numbers, they are just meant to illustrate this a bit ;-)
If you have any questions about this topic, just comment on this blog post! I look forward to your feedback!
Best regards,
Moritz
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