Hi guys,
it's Thursday again and so the next blog posting is here. ;-)
As announced last week, this time the topic is "Trail Braking".
Many drivers divide the braking and turning phase into two separate driving sections. In the end, this is often simply because beginners are not explained and taught why this is not necessarily
an advantage on a race track. Also, Beginners partly take over the behaviour from road traffic (braking before the bend and turning in after the braking process is completed) as they just don´t
know any better.
This classic driving style is also taught in many driving safety or sports driver training courses, which is mainly due to the safety aspect of these courses: If a driver is forced to complete
the braking process before the corner, the chance of him driving into the corner too fast is lower.
But if you look at it from a performance point of view, the classic driving style is not the fastest way to drive around a race track.
That's because the classic driving style requires you to choose an early braking point, which means that compared to trail braking, you're slower throughout the braking phase until you reach the
apex, especially turn in to apex makes a big difference here. The speeds are already relatively low, but at low speeds the differences in speed become even more noticeable.
But what is behind Trail Braking, how do I use this technique correctly and when should I possibly do without Trail Braking?
The technique:
Trail Braking means that you shift the braking process into the corner and decelerate until just before the apex. The idea behind it is, that you can take more speed into the corner and have as
little "dead time" as possible, i.e. time in which you neither decelerate nor accelerate.
From a technical point of view, this means that you start turning while you are still on the brakes.If we now recall the Traction Circle we will see that the action of lateral and longitudinal
forces on the tyre causes the tyre to split its grip and neither the braking nor the steering can be done with 100% of the possible grip.
Excursion: Why smooth is fast
We as drivers must therefore make sure that we make the transition from pure braking to the combined entry into the bend (braking and steering) as cleanly and smoothly as possible. The cleaner
the transition is, the more time the tyre has to build up its grip, because the rubber has more time to interlock with the asphalt. The asphalt is not smooth, it has many corners and edges and
with these corners and edges the surface of our tyre interlocks. And the more time it has to interlock with the surface, the more grip it can generate.
You can imagine it like this: If there's somebody in front of you and you slowly start to push them away, it will take a relatively long time for that person to stumble. But if you push him
backwards with a sudden push, then that person will stumble backwards immediately. So if the directional changes on the tire are slow (pushing the person away), then he will have more time
to interlock with the asphalt. If the steering and the braking are handled very roughly and hastily (pushing the person away), the grip will be lost much earlier.
Now you can of course say: Why shouldn't I use the maximum grip when braking and then afterwards the maximum grip when turning into a corner and make a compromise instead?
This is where the next point comes into play: axle load distribution. Last week I explained how the car's centre of gravity changes when we brake, steer and accelerate:
- When we decelerate, the weight increases on the front tires as the center of gravity shifts forward.
- When we steer, the weight increases on the outer tyres as the centre of gravity moves to the outside.
- When we accelerate, the weight on the rear tyres increases as the centre of gravity moves backwards.
When the weight increases on the tyres, the grip increases as well, because more weight also means more "downforce". And this is what we work with in trail braking.
The fact that in trail braking we have the weight shift to the front (braking) and to the outside (steering) means that the outside front wheel is pressed very strongly into the asphalt and can
therefore transfer considerably more grip than if it only had to transfer the pure steering forces and we make this advantage our own with trail braking: We use the increased grip of the front
tires to take more momentum into the corner in order to gain time.
This is of course much more difficult in vehicles without ABS, because you have to be very careful not to over-brake the inner front wheel. But even with ABS, the driver still has to brake with
feeling, because running over doing the tyre on the brake also causes a performance disadvantage.
The following Video is from a 2019 test for the IMSA GT3 Cup Challenge in Road America, where I was working on the race setup of a 991.1 GT3 Cup and also did reference laps for video and data analysis:
Did you notice a difference in braking technique for the slow corners, like Turn 5 and the very fast T11 "kink"? The faster the corner is, the less trail braking I do. Why? With a very fast corner you try to carry the speed through the corner onto the next straight. If you trail brake into the corner, you might pick up the throttle a little too late and then you lose the run onto the next straight.
That´s it for the topic trail braking, if you have any questions, suggestions or wishes for a specific topic just let me know!
Next weeks topic will be Racing the Nordschleife in the rain ;-)
Many greetings and see you next time,
Moritz