Drivers’ bias towards the brakes

Over recent years a niche solution used by a few drivers has become a standard feature on all Formula One cars – the rapid bias adjustment lever. Adjustable brake bias has been a feature of racecars and Formula One for decades, but until recently, the driver’s control of brake bias was not commonly seen as a means for improving overall lap times.

Drivers have been able to adapt the braking bias from front to rear throughout the race, to compensate for changing conditions. This allows the driver to ensure the rear brakes do not lock up prematurely, to give better stability into corners, and this can make the driver’s lap times more consistent.

Although it has appeared occasionally in Formula One car cockpits over the past ten years, it was Michael Schumacher who really put the rapid bias adjustment system on the map. Since his return to Formula One the field has been tighter, with qualifying ever more important, and the introduction of KERS has greatly affected braking performance.

These factors all affect the distribution of braking effort between the front and rear axles. With ABS or any form of active braking control banned since 1994, the bias set-up at the pedal remains the same through the lap and largely through the race, with only minor adjustments being by the driver from the cockpit.

The distribution of braking effort between the front and rear braking circuits is largely dictated by the relationship between brake pedal and the master cylinders, the force from the pedal being apportioned to each master cylinder by a bias bar passing through the pedal. The bias bar can be moved by means of a threaded adjuster to alter the force applied to either of the master cylinders and thus the front or rear braking circuit. A simple cable operated by the driver on the dash bulkhead finely adjusts the bias bar.

This does not, however, provide rapid or larger adjustments to suit individual corners, changing conditions such as tyre degradation or the loss of the KERS assistance to the rear braking effort.

Although not unique in his use of a rapid bias adjuster, Schumacher found he could gain lap time with a different bias level for different corners, such as braking on gradients and different braking levels for corners of different speeds. So a relatively simple lever arrangement inside the cockpit was devised, which operated the same balance bar as the fine bias adjustment.

With several different bias positions identifiable by detents in the lever mechanism, the German found he could set up the brake bias for specific corners. Often in qualifying and sometimes in the race, he could be seen taking his left hand from the steering wheel and moving the lever before arriving at a corner. But while he clearly found some benefit in the system, which could be adopted by other drivers, it does not fully explain its recent widespread adoption.

The introduction of KERS is one explanation; since 2009 it has affected braking bias braking by harvested energy at the rear axle. KERS is still not completely consistent throughout the race though, either because of different harvesting levels or parts of the KERS being unreliable. Each of these issues will alter the braking effort that KERS adds to the rear axle; for the driver to maintain a constant brake bias through the race, they will need to make more than fine adjustments to the bias bar. Thus the simple control used previously would need several turns of the adjuster to make the required bias shift. The lever arrangement allows the driver to make larger and quicker adjustments, so that if KERS is not harvesting at its full rate then a lever adjustment will quickly compensate. That will still leave the driver with scope for fine tuning using the conventional adjuster.

Most teams now integrate the fine adjuster into the lever arrangement, the assembly typically being sited on the left-hand side of the cockpit, allowing the driver to take his hand from the wheel momentarily to make an adjustment. Both the fine and rapid adjustments are translated into movement at the pedal’s bias bar with a shaft passing from the mechanism down to the pedal.

Although it’s down to driver preference, the lever will feature from three to five detents, tuned to either a KERS compensation – which will shift the bias rearwards to match the lost braking effort from a failed KERS – or with different bias presets to suit specific corners. Thus the mechanism will need to be tuned for different tracks to make the requisite bias adjustment for a specific lever position. As with any driver control its use is largely dictated by the driver’s preference, and can be used in different ways with many different uses.

Next time you see onboard footage of a driver, spare some time to consider the fact that Formula One has found lap time even in the humble brake bias adjuster.

Fig. 1 - In this Red Bull RB6 the brake bias bar can be seen behind the brake pedal (Photo: Craig Scarborough)

Fig. 2 - Williams places its rapid bias adjuster to the left of the cockpit with both a lever and dial for rapid and fine adjustments (Photo: Ionut Pascal)

Written by Craig Scarborough