I’ve coached many drivers who are fast driving away from the apex, and able to reach the exit point of a curve at a good speed (ie, using most of the available longitudinal/lateral grip). But the drivers who are fast up to the apex are less plentiful.
That’s because transitioning from the initial application of the brake pedal until that point where longitudinal G force changes from a negative value to a positive one is the zone where the great drivers hang out.
There’s no doubt that it takes much more skill and finesse to brake well, as opposed to accelerate well.
Over my years of coaching with VBOX dataloggers I’ve come to realise there are four distinct (but paradoxically, with blurred edges) phases in the braking process. I call them Preload, The Big Squeeze, Modulation, and Unsqueeze. I’ve been lucky to have access to data from Clint Weston of the AMG Driver Academy and observing what he does and how he does it at the wheel of an AMG GT has been educational. However, it has only been possible to make accurate assessments thanks to the VBOX HD2 supplying me with G forces (calculated from GPS) and throttle/brake position (this information being extracted from the vehicle’s CANbus).
Let’s dissect them.
· Preload. These nanoseconds are where you’ve moved from accelerator to the brake and taken up the slack. The duration where there is neither brake nor throttle being applied is as little as three-hundredths of a second in Clint’s case, when braking for Turn Two at Zwartkops. The slack in question is in the pedal but also the rest of the car. When talking stock road cars, it includes every rubber bush in the suspension and steering. It is, ultimately, a heads-up to the various mechanicals and systems that a big change is coming to the dynamic state of the vehicle. On the pedal pressure data, you can usually see this as a little up-tick when the pedal position goes from nothing to about five percent - and then very rapidly into The Big Squeeze.
· The Big Squeeze. This is where 90 percent of the action happens. The name sums it up. When I look at the negative G curve and pedal pressure data of a skilled driver, this reveals a rapid build up to maximum forces – in other words, they create a near-vertical G-force line, with the pads squeezed hard against the discs. It is still a squeeze and not a stomp though – compressing the suspension as evenly as possible is still an important goal in the first part of the process. You want the car to hunker down against the tarmac so that each brake can deliver maximum contribution.
· Modulation. Some way into The Big Squeeze you’ll see the G-force start to level off- or even reduce slightly. This is the driver controlling his input as the car slows and the risk of a lock-up or ABS intervention increases. It is a subtle process but you can see it clearly when you overlay Clint and Joe Average. You’ll see a high plateau in the former instance, with an occasional dip. Lesser drivers often have a series of jagged spires, suggesting multiple ABS interventions. Also, the phasing of the process differs, with Clint doing the hardest braking earlier in the entire process.
· The Unsqueeze This phase is critical. More commonly known as trail braking, this is the release of the pedal in a controlled manner up to the point where the foot can be transferred to the gas. The objective is to keep the front end of the car sufficiently loaded to aid steering grip, the first, subtle movement of the steering already having been made. With the car starting to pivot/swivel around its front axle (aided by the rear being slightly unloaded), the final release of the brake pedal can be made. Get the "Unsqueeze" wrong and you’ll overload the front tyres at some point on your way to the inside of the corner, creating an initial understeer and moving the car away from the target enough to make hitting the apex impossible. Miss the apex and it is virtually impossible to get on the gas soon enough and hard enough to get perfect drive onto the next straight.
Further around the lap, the process starts again but it isn’t identical. Turn Four at Zwartkops, with an apex speed of 110/115 km/h - versus just on 60 km/h for the hairpin - is a momentum corner and the G-force curves Clint creates are very different - understandably so, when you consider they have little in common other than being right-handers.
What he does at two totally different corners has convinced me that braking is of the essence and that it becomes even more of a delicate art when driving a traditional manual, and a car that doesn't have ABS. I'm keen to get the VBOX onto something like a Backdraft Cobra with a Reghard Roets at the wheel, or a Lotus Challenge car with Jeffrey Kruger driving and take a close look at their data when they're working the middle pedal...