Intended more for assisting workmen driving around on slag heaps, ferodo’s DS11 friction material turned out to be ideal for braking the world’s top racing cars for two decades. Never has a component enjoyed more success, says Keith Howard
Few components have enjoyed such along reign at the pinnacle of motorsport that they can claim a tally of grand prix victories reaching into three figures. Koni’s 8212 damper — the subject of an earlier Technofile — is one exception, with a magnificent 186 victories to its credit. But even this achievement pales next to that of Ferodo’s DS11 friction material, which braked the winners of all but two grands prix between 1961 and 1981: 265 victories from 267 races. DS11 dominated braking in F1, and a lot of other formulae besides, almost from the adoption of disc brakes as the sine qua non right up until the arrival of carbon-carbon.
You might suppose that to achieve this feat DS11 was painstakingly formulated at Ferodo’s HQ in Chapel-en-le-Frith, Stockport precisely for the purpose of anchoring racing cars. Only that isn’t the case. It was originally formulated as one of a series of products intended for continuous heavy duty use, which means it was conceived for industrial applications or perhaps heavy vehicles. It just turned out to be the best material in Ferodo’s inventory for use in the senior racing formulae, and actually wasn’t the first of the DS series to be seconded to this task. Before DS11 established itself as top dog, DS3 and DS5 both saw service.
Paradoxically, the significance of DS 11’s arrival in F1 was not that it improved the cars’ braking performance as such. Actually, it helped them go faster, both along the straights and round the corners.
In any racecar — or road car for that matter — the brakes must be powerful enough to lock the wheels, so that ultimate braking performance is dictated by the friction between tyre and road surface. DS11 did nothing to change that. But its superior fade resistance and wear performance at very high temperatures did permit brake rotor size and/or the amount of cooling air ducted to the brakes to be reduced.
Both these changes translate into improved lap times. Smaller brake ducts reduce aerodynamic drag, improving a car’s straight line performance. Downsizing brake rotors also assists acceleration, for the reason that the rotational inertia of each wheel/hub assembly ‘steals’ motive power. To rotate a wheel faster there has to be an input of energy, and there is only one place that can come from — the engine. Reduce the size of the brake disc and the rotational inertia of the wheel/hub assembly is reduced too, freeing up a little engine power for acceleration.
Cutting brake mass also reduces the overall mass of the car, of course, so the acceleration benefit is compounded. And a lighter brake disc also means less unsprung mass, which reduces fluctuations in the force pressing tyre to track surface, referred to in the jargon of suspension kinematics as dynamic tyre load. Reduced dynamic tyre load translates into improved grip over uneven surfaces — and all track surfaces, even apparently billiard table smooth ones, are uneven to some degree — so the car will also corner faster, and enjoy improved traction. By the same token it will also brake a little better, so my opening claim that DS11 did nothing for braking performance perse is not absolutely true. The important point is, the benefits were more far-reaching.
All friction materials of this period relied heavily on asbestos. A high proportion of DS11 comprised randomly aligned chrysotile (white) asbestos fibres, bound together by a matrix of various resins. Asbestos wasn’t only highly resistant to elevated temperatures (it only breaks down completely above 1200C), it also enjoyed the advantage of good chemical compatibility with the resin materials, something not true of the Kevlar, steel and other fibres that would be called upon to replace it when health concerns finally dictated its deletion from the brake compounder’s toolkit.
In DS11 ‘s case the other key ingredient was finely divided copper powder, to improve fade resistance and reduce wear. This and the other constituents were first mixed together in a rotating drum, then added dry to the pad mould and compressed under high pressure. Although the friction coefficient of the finished material was only a modest 0.31, this was retained to above 600C, with a recommended maximum intermittent operating temperature of 750C. Only above this temperature would the material start to fade and the wear rate become unacceptable, so racing drivers could hammer the brakes as never before — although they had to remember that DS11 was notoriously unresponsive at low temperatures, so the first couple of corners had to be approached with caution.
There were also some subtleties to realising DS11’s full potential. First the pads had to be bedded in carefully over a couple of practice laps, to remove any high spots in the contact with the disc, then used hard for a lap to heat condition them, and lastly cooled during a slower in lap. Only then were they ready for race use. Drivers who tried to short-circuit this procedure risked compromising DS11’s performance. Be too gentle with it, though, and it could form a tough, polished surface that generated little friction and was very difficult to break down, an outcome known as glazing.
Ferodo technicians attended every grand prix to monitor brake temperatures and advise the teams on cooling requirements. Particularly at circuits which were hard on brakes, they would keep a keen eye on drivers known to be brutal with the brakes, certain that if they were within the temperature limit then other drivers would be too. Three temperature sensitive coloured paints were applied to disc rims to monitor peak temperatures out on the track: green, which would turn to white at about 430deg C; orange, which would turn yellow at 560deg C; and red, which would turn white at 610deg C. When the brake cooling was optimum the green would have turned completely, the orange would be just beginning to, and the red would remain untouched.
Other single-seat formulae, endurance racing, touring cars and rallying also embraced DS11, and even after carbon-carbon ousted it from F1 it continued to be successful in race series in which carbon was banned. It was, without question, the most successful motor racing friction material there has been. And to think: it might have squandered its days braking earth-movers.