It took seven years for carbon brake discs to make their mark. Now F1 would not be without them. Keith Howard recalls one man’s quest to make them work.
So long have carbon brakes been standard fitment in Formula One, it’s easily forgotten they were once the subject of ribaldry in the pitlane and, but for one designer’s vision and clogged determination, might never have become a hi-tech icon of the sport. That man was Gordon Murray, who during the period in question was chief designer at Brabham under Bernie Ecclestone.
In the mid-70s Murray was still a new kid on the Grand Prix block, and a self-confessed admirer of the innovatory approach to race car design epitomised by Colin Chapman. Like Chapman, he looked to the aerospace industry for inspiration and so it was that in 1975 he read, in one of the aircraft magazines, of the carbon/carbon brakes developed for Concorde by Dunlop Aviation. Considerably lighter than the conventional equivalent, with a higher coefficient of friction, and able to operate at elevated temperatures without suffering fade, they looked, on paper, an F1 designer’s dream. In them, Murray recognised immediately the future of Formula One brakes.
Surtees tested some prototype carbon/carbon brakes during the winter of 1975/76, beating Brabham to the first punch, but it was Murray who took the technology to the race track the following season. McLaren’s carbon fibre tub was still five years away, making Brabharn’s one of the earliest applications of the material in Formula One. But whereas the carbon fibre monocoque was an instant success, developing the carbon brake into a race winner was to prove a long, hard slog. In the event, the carbon chassis notched up its first Grand Prix victory a full season before the brake.
Not that the carbon composites used for chassis construction and brakes are the same, despite both containing carbon fibre. In the former the fibres are bound together by an epoxy resin – a tough material, but incapable of sustaining the 2500 deg C that carbon brakes can withstand. For that feat of temperature tolerance a binding matrix of pure carbon is needed hence the fuller carbon/carbon description to distinguish the finished material from carbon/epoxy which is deposited on a fibre blank using a process called carburisation. Essentially, the blank is heated to 2000 deg C in a methane atmosphere, causing the gas to dissociate and lay clown carbon between the fibre strands. Uniquely, both discs and pads are made of the same material.
Formula One presented a very different design challenge from Concorde, and Dunlop was deeply concerned from the start of its collaboration with Brabham that the thermal characteristics of carbon – which were to dog its development – precluded conventional mounting of the disc on an aluminium bell. So it devised what, with the benefit of hindsight, appears a distinctly odd sandwich of carbon and steel. A 0.125in thick steel plate, incorporating mountings to the wheel hub, formed the meat, with 20 pucks of carbon/carbon, ten per side, arrayed radially on either face. Ironically, rather than solving the thermal problems, this structure was actually to demonstrate them rather spectacularly.
Having successfully tested the new brakes on the BT45, the decision was made to use them in a race for the first time at the Nurburgring that year. Carlos Pace afterwards described them as `spongey’; Rolf Stommelen was more positive. But at the Austrian GP at the Osterreichring, with them fitted to Pace’s car, disaster struck. Sudden brake failure on lap 41 precipitated a big enough accident to wreck BT45/4 completely. Differential expansion between the steel and carbon, exacerbated by uneven cooling, had caused a disc to warp and rub against its caliper. The resulting heat boiled the brake fluid, leaving the hapless Pace brakeless. His foot went to the floor and the car quit the circuit.
It was just one in a succession of thermal problems that were to see Brabham’s first-generation carbon brakes largely confined to practice sessions for the remainder of 1976 and beyond. Unlike cast iron, carbon has low thermal conductivity, so heat has to be removed from its surface rather than via internal ventilation channels. When a carbon brake begins to glow above 500 deg C, only the very outer half millimetre or so of disc material is involved. This wasn’t appreciated in the early stages, resulting in high levels of heat radiation into the caliper, which could boil the brake fluid, or into nearby components like wheel bearings, whose grease could melt.
A second, quite different thermal problem came to light when the carbon/carbon brakes proved to be suffering unexpectedly high wear rates. Although it was supposedly compatible with temperatures of over 2000 deg C, at sustained heat of above about 700 deg C, unswept areas of the material began to oxidise. Effectively, the disc would begin to evaporate. A paint coating was duly developed to suppress this, but carbon brakes were never to operate at the extreme temperatures originally envisaged.
For the BT49 of 1980 Murray made a fresh start with US carbon brake manufacturer. Hitco, which was confident a solid disc could be used, mounted to a conventional bell. Now the carbon brake began to look as we know it today, although it still remained confined to use in practice and qualifying while the development process painstakingly continued. Not until the Brazilian Grand Prix of 1982 did Nelson Piquet give carbon/carbon brakes their first race ‘victory’, at which juncture – notwithstanding the fact that the car was subsequently disqualified for being underweight – others in the pitlane belatedly decided they wanted this technology too.
Hitco couldn’t oblige – its deal with Brabham was exclusive – so they were .forced to look elsewhere, to French aerospace supplier Carbone Industrie, and it took them two years to catch up. In the interim Hitco’s carbon brakes helped Piquet to the driver’s championship in 1983, at last vindicating Murray’s stubborn persistence. Would carbon/carbon have elbowed its way into F1 without his efforts? Possibly not, because in later years – particularly with the arrival of sintered carbon metallic friction materials – cast iron brakes in many respects caught up. Friction coefficients are now about the same, as is the range of acceptable operating temperature. When Damon Hill tested cast iron brakes at Williams in 1995 he and the team reported little obvious difference, deflating arguments that outlawing carbon/carbon would improve overtaking opportunities.
Carbon discs do retain one clear benefit over cast iron equivalents, though: they are about a quarter the weight, saving perhaps as much as 5kg per corner on unsprung mass. It’s a critical advantage, and, as such, one that’s still well worth having.