HOW TO TRAIL BRAKE
Written by Scott Mansell - EuroBOSS F1 driver and top UK race instructor. You can always improve your track day driving with instruction; the best way to be a safer, quicker & more confident driver.
WHAT IS TRAIL BRAKING?
Trail braking is a technique I hear a lot of people talking about when working at track days, but one I rarely see being fully utilised or carried out properly.
Trail braking is the term used to describe the technique of continued braking whilst turning into a corner: braking and turning at the same time. It enables a driver to brake later and manipulate weight transfer to perfect turn-in.
THE SCIENCE
The first things to consider are the tyres. They have limited grip under acceleration, braking and turning. It is possible for the car to individually accelerate, brake and turn utilising 100% of the grip available in that direction; however it cannot carry out a mix of braking and turning at 100% of each.
The diagram, shown right, shows the ‘Grip Circle’ of a car and its tyres. Initial braking is at 100% and in a straight line, but then as the car begins to turn the braking has to become less as the tyres simply cannot do both. The more the car turns, the less braking is possible, until the foot is completely off the brakes and the car is at it’s turning maximum.
Once the car is at its turning maximum it can then begin to accelerate again - although the turning percentage will have to decrease. This is when you release steering angle as you come off a corner.
The drawing to the right shows the same theory of the 'Grip Circle' but it is shown as the car makes its way around the circuit.
- The car is braking in a straight line and so it can brake to 100% of its potential.
- The car is entering the corner with slight steering angle and so brakes have to be released a little.
- Deeper into the corner the car is turning more and so the brakes have to be released even more.
- The car is now at its turning maximum and so the brakes are fully released.
The graph shown right shows a real data trace of longitudinal and lateral G during the braking and entry to a right hand corner.
It demonstrates how a car only has a finite amount of grip to utilise and how the two processes should overlap with each other.
WHY DOES TRAIL BRAKING MAKE ME FASTER?
Trailing the brakes mean that you have the possibility of using 100% of the tyres grip from braking to the apex of a corner.
If you do not trail brake there is a period (from release of braking to apex), where there is spare grip available. Overlaying your braking and turning means that you can use the entire grip available in this section of cornering.
In the diagram (below, right) you can see a speed trace taken from the data logging seen previously, showing the speed differences between trail braking (blue) and no trail braking (red).
As you can see the blue line carries much more speed to the apex, whereas the red line does not utilise the cars grip as well as you should.
HOW TO TRAIL BRAKE?
Trail braking is quite a difficult technique as it requires a lot of feel and balance to be carried out correctly. However, with the knowledge, practice and perhaps an instructor it’s a new skill that can be learnt over a relatively short amount of time.
The main thing to think about is the Grip Circle. To reiterate a section of this fundamental theory: you cannot both brake and turn together, as much as if you carry out these events by themselves.
Therefore, when you are entering a corner you must be reducing braking as you increase steering angle.
When you are driving on track you cannot be thinking about numbers and percentages; it is all about feel. You need to feel whether traction is about to break and this requires a good amount of practice.
Always remember the fundamental rule of being as smooth as possible; be very gentle as you are removing the brake as you smoothly turn in. If you try to turn in too fast or with too much steering angle, you are guaranteed to oversteer and have a possible spin. Let that be a warning!
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