Dynamics optimisation and construction of Formula One brake pedals
A driver’s ‘feel’ for braking is perhaps one of the most critical aspects of racing. As much as the talk of brake disc/pad materials, it’s also the kinematics of the brake pedal that are crucial to giving drivers what they needs at their foot.
Fundamentally unchanged in its design for decades, the brake pedal is at in essence a simple part, being a pivoting lever with a plate for the driver’s foot and a bearing housing midway up the lever for the bias adjustment mechanism. However, the detail design and construction have evolved massively into optimised, stiff and light brake pedals.
Since the advent of clutch paddles on the steering wheel, all Formula One cars feature just two pedals, and the driver operates the brake exclusively with his left foot. To this end, modern Formula One pedals feature large footplates with flanged sides, as the driver does not need to slip his foot to operate a clutch or ‘heel and toe’. Each driver has a preference for the design of the footplate, which often has a grippy abrasive material applied to its surface.
Driver preference goes even further with the detail design of the pedal and its interaction with the hydraulic elements of the braking system: teams will optimise the dynamics of both the mechanical and hydraulic elements of the brake bias adjustment mechanism. Ideally the driver wants a bias that shifts during braking, which isn’t possible using active control systems, but by designing the bias bar and valves in the system it is possible to get this behaviour. Everything from the fluid properties, orifice sizes, pipe compliances, bias bar mass, inertia and friction characteristics has an effect. Teams will model these variables in modelling software to design the ideal braking set-up for a specific driver.
One team found an issue when one driver applied the brakes at ten times the velocity of the other driver.
Being only some 240 mm tall, with the bias bar just under half that distance from the pivot, a driver pressing 130 kg with his leg under braking puts great stresses on the pedal; the catastrophic effects of a pedal failure do not bear thinking about. Thus the construction of the pedal has evolved over the decades, from fabricated steel pedals, through the use of titanium, machined aluminium and latterly carbon fibre. With such optimised design the weight of the pedal is now 200-300 g.
These days, Formula One teams are still split between carbon pedals and machined aluminium. One contemporary aluminium pedal seen by the author eschews the simply bar design for an almost semicircular arrangement, where the master cylinders attach to this triangulated shape for even greater stiffness.
It’s also now common for the bias adjuster to be mounted to the bulkhead, and the master cylinders directly to the peal. This frees up space in the footwell for the adjuster cable to reach to the bias mechanism.
Fig. 1 - Moulded carbon fibre and fabricated steel Formula One brake pedals
Written by Craig Scarborough