Braking on the Limit
This is developing the maximum braking force from the tyres up to the point where they stop turning. By virtue of the fact this style avoids locking the tyre, it is the fastest way to stop in a vehicle, with or without ABS.
A skilled driver with good observation skills and sensitivity underfoot to manipulate the pedal can apply an infinite range of brake pressure to match the conditions to stop the car in the shortest possible distance.
Instructions from your foot apply pressure to the braking system, which creates reverse torque at the wheel hubs, causing the tyres to slow down just before the car does. When things are going well, the tyres will be turning about 15% more slowly than your road speed before they begin to lock.
The tyres streeetch, and their elastic force pulls the speed off the car. As brake pressure increases, there comes a point where the tyres begin to slip before the wheels actually stop turning and lock up. That point is the braking limit, the threshold beyond which the tyre starts to skid.
Your brain detects these minute changes in physical forces through a mix of experience, the varying pressure you get from your body pushing into the belts and your sense of speed. Honing that ability requires familiarity with your car, feel for the conditions and practice in a safe environment.
The world’s finest racing drivers have an innate sensitivity for the available grip and tread the pedal with surgical precision, prompting the adulation ‘he was the last of the late brakers’, often a reflection in the past tense, since the bravest brakers also tend not to live long. Sometimes it pays to be the guy who brakes first…
It always pays to optimize the circumstances for braking. Wherever possible you aim to brake as much in a straight line as possible so the tyres can focus on one job only.
Your front tyres alone perform more than 60% of the braking, and to help them do this you want to transfer some weight onto them. Here’s the trick, and it flies in the face of my philosophy about resting a glass of water on the dashboard.
In dry conditions, you initially stab the brake pedal to shift weight forwards onto the fronts and then squeeze until you reach optimal pressure, modulating as required. You dig your foot about an inch into the brake pedal, and the nose dives as weight shifts quickly onto the front tyres. The more weight bearing down on the fronts, the harder you can then squeeze the pedal. Remember to keep the heel of your foot on the floor so your foot is adjusting the pressure on the pedal rather than your whole leg.
Braking gently doesn’t send enough weight onto the front tyres and they will never develop their full braking potential regardless of how hard you brake later.
Much better is a squeeze. The first touch is immediately followed by a more gradual but firm building of pressure, hopefully based on the good foundations laid by the initial stab. You increase pressure to the point where you can feel the tyre almost start locking. In your average road car the foot pressure is around 40 pounds, or the weight of two watermelons.
You also need to know how to modulate the brake pedal. Limit braking is based on constant, instinctive assessments of the available grip. When it’s going well, it’s just fine-tuning as you feel how much the tyre is biting from one moment to the next. On bumpy country lanes, things can get quite lively.
This style of performance braking is equally valid in cars fitted with ABS. You can perform an emergency stop, but I try to avoid triggering the computer and drive to the threshold of the tyre, the point before locking. The friction of a stopped tyre when the vehicle is travelling at high speed creates an enormous amount of heat and the molten rubber causes extra slippage. This kind of overload needs to be rectified early on by quickly releasing pressure on the brake pedal and then reapplying. This technique is known as Pulse Braking.