When you're learning to race, whether it be on a simulator or in the real world, you may not think about the way you brake.
Chances are, you will just mash the brake pedal, try to turn in, pick up a ton of understeer, and be on your way, or crash or spin, depending on the car and conditions.
Or, you'll mash the brake pedal, and then completely drop all brake pressure and try to turn in, pick up a ton of understeer or lift off oversteer, and be on your way, or again, crash or spin, depending on the car and conditions.
You never really tend to think about what you should be doing. How smooth you actually need to be with the braking.
Basic logic might suggest a simple formula for braking into a corner:
Braking harder X braking for longer = stopping quicker
In reality, that formula would work if stopping in a straight line in a car with ABS. Without ABS, you would lock your tyres and skid. If you tried to do the same formula into a corner, it look like this:
Braking harder X braking for longer = Lock up/Understeer/Wall
You get the idea. But why does this happen?
Weight (load) transfer
Weight (load) transfer is exactly what it sounds like. The transfer of load from one place to another.
Now imagine when a car is sat still. It's weight distribution is as stable as it will ever be. It won't change. This does not necessarily mean the weight distribution is equal front to rear in this scenario. Most cars have more weight to either the front or rear.
We refer to front weight as X and rear weight as Y
Say a car has a weight distribution of 40 X /60 Y that would be the stable weight distribution of the car.
Weight transfer (better called load transfer) is a natural phenomenon that occurs because of the existence of inertia, that happens when you try to change the state of motion of the car.
Doing acceleration or braking, you change the longitudinal velocity of the car (the longitudinal speed of the car as it moves in a forward direction).
Notice the front of this BMW squat during braking. This is load transfer, visible because of body roll, which is the suspension responding to the effects of weight transfer.
During acceleration, load is transferred to the rear of the car, which is why you'll see a car squat down on it's rear and lift slightly at the front during acceleration. During braking, load is transferred to the front of the car, which is why you'll see a car dive down at the front and lift slightly at the rear during braking. This occurs on every vehicle, although it will be more visually noticeable on a car with a softer suspension, as there is often more body roll. Body roll is not the same as weight transfer, but it can be used to see the effects of weight transfer.
The point is that during braking, as you use a full or a high amount of brake pressure, you push the nose of the car into the ground, and the load is transferred onto the front tyres. This is fine braking in a straightline, because you are only asking the tyres to do one thing, which is to slow the car down when you apply the brakes.
The problem occurs when you try to turn at the same time. The rear of the car is unloaded, and the tyres are not therefore not 'biting' into the track, at which point they are no longer able to provide maximum grip that would be available if they were.
Now stick with me here, this might sound a little complex, but it does make sense.
Let me. S
To imagine this better, think of a car not moving. We'll give each tyre an imaginary grip number, with the perfect amount of grip always being 100, whether the car is moving or not.
At a standstill, each tyre has a value of 25. 25x4=100. This is because there is no force acting on the car and the grip is evenly distributed.
It is important to understand that once the car is moving, the level of grip available to the 4 tyres combined will never total 100, unless no force is acting upon the car. This is because of that load transfer we spoke about earlier - the loaded tyres gain in grip will always be less than the unloaded tyres grip loss, hence the overall grip loss.
So when the nose is pushed down under braking, the front tyres are being pushed into the circuit more, giving them more grip, let's say 30/30. Meanwhile the rear tyres are now unloaded and not being pushed into the circuit, therefore grip level is reduced. So let's say the total level of grip that is physically available now is 90, and the car is braking in a straight line so the grip is even across the axle, the rear tyres have 15 each, leaving front 30/30, rear 15/15.
Now when you turn into the corner, lateral load factors in. If you turn right, the load transfers to the left side, and if you turn left, the load transfers to the right side. We will explore this in another article.
So let's say now the total amount of physically usable grip is still 90, but this time the tyres with the most grip are on the side opposite to which the car is turning, because the load is transferred to that side.
Let's say we're turning right.
The left hand tyres will have more grip than the right right hand side tyres because of the lateral transfer.
So, the left front and rear would have 30 grip "points" each, with the right front and rear having 15, to total 90.
The example I've just explain is a scenario where you are using the maximum grip avaliable, minimising the effect of weight transfer. Trail braking is how we achieve this.
Trail braking allows for a smoother transition into slowing and turning, causing less weight transfer and therefore allowing the maximum level of grip to increase. As max grip increases, so does max speed able to be carried.
The more you turn, the less you brake. Steering and brake inputs should be parallel (corresponding) to each other in this respect.
Do not lift off the brake completely however, as the dwindling yet remaining amounts of brake pressure are helping the front tyres (the rotational tyres) to turn the car, by still pushing into them into the circuit. So the front tyres will still have more grip than the rear tyres, but the rear tyres will be at their individual max grip limit, in addition to the fronts.
This will allow all four tyres to get much closer to that 90 number of maximum available grip. And with correct steering inputs too, reach it.
This skill will take time to learn. You will get better the more you do it. PRACTICE, PRACTICE, PRACTICE.
I will leave this article with a step by step guide to tackling a corner with the trail braking technique
1. Brake in a straight line at maximum brake pressure
2. Reduce brake pressure gradually as you turn into the corner - this should be a linear (gradual) process, in parallel with your steering input. The more you turn, the less you brake. Don't reduce brake pressure to zero, unless you have too much rotation, in which case lifting off can be a way to induce understeer into the car.
3. Aim to have completed braking and begin accelerating by the apex of a corner in an optimal scenario.
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