Back to contention: The 1997 McLaren F1 directional stop

Back to contention: The 1997 McLaren F1 directional stop

Monday, March 1, 2021 by René Fagnan

A car driving on a roundabout must accelerate, brake and negotiate turns. And since nothing is perfect, almost any car that turns to negotiate a turn produces what is called understeer.

The front tires, the ones that steer the car, have less grip. If you turn the wheels too much to take a quick turn, the tire sole no longer adheres, slips and causes the front axle to slip. It understeer; A big problem in racing, because it forces you to negotiate curves more slowly than necessary.

There are two ways to turn a car: steering that turns the front wheels, or slowing down the inside wheel. It is this second solution that is used to turn a tank or a bulldozer. You should speed up the outer caterpillar and slow down the inner caterpillar.

Working on the rear wheels of a car to help turn and corner is nothing new. Some production cars, such as the Honda Legend and Mitsubishi 3000 GTO, are equipped with four-wheel steering systems, that is, a device that allows all four wheels to be steered during cornering to facilitate maneuvering. If the front wheels turn to the right, the rear wheels do the opposite and turn to the left, causing the car to spin. This device was also used in the Andros Trophy ice racing cars.

In 1993, the Benetton Formula 1 team developed a “C” version of its B193 with a standard Ford HB V8 engine. To make this seat faster on slow circuits, the engineers had fitted it with a four-wheel steering system. The rear axle of this single seat was fitted with a hydraulic rack that rotates the rear wheels according to information received from several electronic sensors. Considering that it was a driving aid, the FIA ​​quickly banned any device that allowed the geometry of the rear suspension to be adjusted.

Discreet braking

Enter the McLaren team engineers, including Adrian Newey, Steve Nichols and Paddy Lowe. It was Nichols who came up with the first idea of ​​a differential rear brake or directional brake where using the brake made it possible to produce a yaw movement (pivoting of the vehicle in the direction of the bend).

The 1997 McLaren MP4/12 with the V10 Ilmor (Mercedes-Benz) aero engine is equipped with a second brake circuit and an extra pedal. “We just had to add an extra master cylinder to the car and connect it to the left rear caliper,” says Nichols. “When the driver entered the left turn, he pressed the normal brake pedal, which activated four disc brakes, front and rear. From the top, the car usually had a tendency to slow down. To counter this, the pilot then pressed an additional pedal with his left foot which only applied the left rear brake. We have adjusted everything so that the pilot has to press this pedal hard to get the reduction effect. If this pedal were too sensitive, braking hard would cause the car to spin”.

At the beginning of the 1997 season, this technological innovation only allowed standing on one side of one seat. It was decided by the engineers, based on the number of corners to be covered on the track. If there were more right turns, they put an additional brake circuit working on the right rear brake, and vice versa if more curves were on the left.

Mika Häkkinen used the paddle on his steering wheel. So his car had only three pedals: the accelerator, the normal brake and the directional brake. His teammate, David Coulthard, was a traditional rider and still used a foot peg. His pedals, already very tight, had four pedals!

The engineers had also spent time to ensure that their machines followed the technical regulations of the letter. The rear suspension of the MP4/12 stayed perfectly in the turns proved its compliance.

Later, the technicians improved the system by adding another master cylinder and several pipes. This time, McLaren had two new suspension loops. A toggle switch, located on the steering wheel, allowed the rider to select the rear brake to activate depending on whether it was a right or left turn. Additionally, this device also helped reduce rear wheel spin out of corners and reduced lap times by nearly half a second.

On the other hand, Newey was concerned that the rear brakes would overheat if misused. Saving on the brakes was not part of Häkkinen’s vocabulary… So the team had to send a secret message during the race to warn him not to abuse the directional brake.

The use of this special brake was discovered by the British photographer Darren Heath who was surprised to see in his photos that the rear discs of McLarens were orange and hot when the car accelerated (see the rear brake in the photo above). Heath remained alert and was able to take pictures from inside the cockpit of Häkkinen’s McLaren, which had been left unattended after the Finn retired at the Luxembourg Grand Prix. Extra pedal: the cat is finally out of the bag.

Ferrari didn’t really appreciate the McLaren’s braking system. Unable to get its system to work properly, the Scuderia then convinced the FIA ​​to ban it. He was banned from the Brazilian Grand Prix, the second event of the 1998 season. He did not appear again in F1.