It’s a given fact that as a race progresses, the wear on the consumables will change the handling balance of any car, regardless of how well it’s set up prior to the race. Of course, the most clever engineers and drivers will ensure a car changes very little and maintains a semi-consistent personality, but inevitably, the balance will shift a bit.
To adjust the car’s willingness to turn into a corner, especially when the front tires are shot, one can shift the brake balance rearwards to provide a little rotation from the rear axle. Essentially, a rear axle that can brake more effectively also has the ability to help turn the car. This can be useful, though too much of it can be quite dangerous, as the car will eventually want to spin. The ideal is found somewhere between these two ends of the spectrum.
Additionally, shifting brake balance towards the rear, as is suggested in the preceding paragraph, diminishes overall braking performance. It’s true that on most racing cars the front brakes are larger than those on the rear axle, so cutting the fronts out of the equation too much will make attacking a corner a real ordeal.
Having a braking bias that favors the front wheels is great for many types of corners, mainly because it’s safe and dependable. It’s hard to send the car into a spin from braking too hard, and therefore this type of balance is wonderful for high-speed corners, where the car is on more of a knife-edge. Too much trail-braking here isn’t always safe, however, but that also depends on the aerodynamic balance of the car.
Front-biased braking generally works in straight-line braking zones, as well as hard braking zones. It offers slightly more braking force and is more reliable; the car is less likely to spin. However, it also has the effect of straightening the car out and keeping the front tires from being too responsive.
This setup is favorable in shorter, slower corners, where the driver is trying to get the car to rotate with the brakes. It is slightly more stable when the driver is trying to brake and turn at the same time, and is less likely to lock the rear tires, which is a surefire way to spin.
Adjusting the brake bias can be done with just about any modern racing car, and if one is needed, buying a brake bias adjuster will not break the bank. They can be used to accommodate for changing fuel loads or reduced tire grip, but they can also be changed corner to corner on one lap.
If a driver finds themselves in need of a little more braking power at the expense of rotatability, they can shift the bias forwards to grant stability and confidence in a heavy braking zone. If the corners that follow don’t require much braking effort, they can shift the bias backwards slightly to help the rear end point the car in the intended direction as it enters the corner.
Determining how much to shift the weight also depends on the platform and the shape of the road. If the car is very stiff, like a prototype or a formula car, and is going to shift weight more quickly, the balance does not need to be changed as much as it would in a softer sedan racer. Additionally, if the car is braking on an uphill slant, the bias can remain rearward, since the incline will prevent as much weight from shifting forward onto the front brakes as if the road were totally flat. The opposite applies for downhill braking. It also depends on the weight distribution of the car and how that affects braking performance.
There are a multitude of variables which determine how well a car could and should brake in these sorts of situations, and getting the most out of them requires feel and an ability to adapt, instead of relying on the ideal balance. However, for the ultimate performance, a clever driver will constantly change the bias to help get through the corner in one piece, and this will help save their tires in the long run since proper adjustment reduces the chances of brake-lock. It’s a tricky game measured in tiny steps, but one that makes a whole world of difference if done correctly.