Brake bias is the distribution of braking force between the front tires and the rear tires. There's a very common misconception that more brake bias on the front means more grip. That's not true, because it will be using more of the traction available until it reaches the limit and the friction is not enough, so the tire locks up and starts sliding, causing zero lateral grip and decreasing longitudinal grip due to kinetic friction and overheating.

This is true even if you're not locking. If you add more front bias, the car is going to turn less because there's going to be less lateral grip. Locking is not like an on/off thing. It starts microlocking, you start losing grip and progressively get to the point where the car is moving and the tires are not. But it's a progressive thing and the closer you get there, the less grip you have.

Brake Bias on a Straight Line

On a straight line, we want to maintain all four tires on the limit of the longitudinal grip, ideally locking up all four tires at the same time, at least theoretically. Because if you have the brake bias too far from balanced, the end without the bias will not reach the longitudinal grip limit and the car won't stop as quickly as it should.

Brake Bias While Cornering

We don't brake only while on a straight line, we also do it while cornering. So how does brake bias affect the balance of the car while cornering? We want to find the brake bias that maintains a healthy rotation while trail braking without locking too much the fronts or the rear tires while cornering.

• Less brake bias to the front (or a lower brake bias percentage) will mean the car will have more front grip and rotate more under trail braking

• More brake bias to the front will mean the car will have less front grip and understeer more while trail braking

Understanding Front Grip and Brake Bias

More front bias means more grip used by the front for stopping. Therefore, less remaining grip for turning. So when we say that rearwards brake bias means more front grip, the right way of saying it is more rearwards bias means less resistance to turning on the rear tires, which feels like more front grip. Because in a way, you're not adding grip to the front tires, you're actually removing grip from the rears. But it feels like you're getting more rotation. So that's why it's so common for people to say less brake bias, more front grip.

Advanced Driving and Brake Bias

At a higher level of driving, generally a lower brake bias than the safe baseline setups is ideal. So if the baseline is say 65%, then it's probably going to be faster if you go down to 63 or 62. But it might require that you get much more precise driving because it might be a little bit too oversteer on entry. The way we're going to fix that is we're going to adapt to the new more sketchy way of driving, which we're going to discuss in the cornering module.

Understanding Brake Bias Percentages

Normally, the setups have a brake bias that locks the fronts more easily. But for some cars, 60% might be actually very low, and you might actually lock the rear tires. It really depends on so many factors like setup, tires, etc. Because when you start braking, a lot of weight goes to the front tires, then it's normal that some cars have a lot more brake bias on the front to prevent rear locking because the rear lifts and has a lot less grip. So for some cars, 55% is actually very low and you're going to spin right away if you start braking too hard with that.

The Challenge of Perfect Brake Bias

Here's the question: is it possible to have a brake bias that satisfies both straight line grip locking all tires at the same time and the cornering grip locking front inside and rear inside at the same time? That will depend heavily on car setup. It's actually quite difficult to make that happen. It's possible to lock the rear tires first when breaking in a straight line, and then as soon as you start turning, you lock the front tires first as you're turning, especially if the setup of the car is off balance.

Many times we will have to sacrifice the straight line braking balance in order to get a better rotation control while cornering. Always prioritize cornering balance for your brake bias. You will hear a lot of people saying that you should set your brake bias so you lock the fronts and rears at the same time in a straight line. But if you only do that, you may find yourself struggling to rotate the car properly while trail braking.

Example: Understeer Setup

Here's an example. An understeer setup where the car does not want to turn at all. We end up needing a much lower brake bias to make it turn while cornering. But that will cause the longitudinal grip to be a bit off, causing the car to lock the rears first on a straight line if you go over the limit. In this case, you would have to maybe even lose a little bit of braking performance to benefit the cornering and find the best compromise. If you cannot change the setup, trial and error is the only way to go until you find the best compromise.

Extreme Example: Variable Brake Bias

Here's a crazy example. During a high level Formula 3 league, the car was ultra oversteer on lower speed corners but understeer on high speed corners because of the balance of the setup. The aerodynamic setup was all over the place. The setup was fixed so we could not change anything but the brake bias. The solution was to use 55% brake bias on lower speed hairpins but then bring it down all the way to 45% brake bias during high speed corners where the downforce was giving way too much grip to the rear tires and not enough to the front tires. This is an extreme example but it happened.

Suspension Setup and Brake Bias

Cars with stiff front suspensions generally lock up the front tires while cornering very easily. Because when you start turning into the corner, the inside front tire can get unloaded so much that it even lifts. This is also possible in GT cars. Be careful with one thing: if you abuse the steering wheel mid corner, like turn way too much, it's possible to lock up the fronts even if the brake bias is very low.

Effects Beyond Locking

These effects—more rotation, less rotation when trail braking—can be felt even when we're not locking. We will still be stressing the tires and affecting the balance of the car during trail braking. There will be situations where no matter the brake bias, you will still lock up the inside front when turning because of the front tires lifting and not even touching the track. We will discuss this more in detail at the terminal trail braking pressure in the next module on cornering.