Making Them Stop
The Editor Comments on the Progress made in Braking for Racing and Rally Cars, with Particular Reference to a Visit to Ferodo Limited at Chapel-en-le-Frith.
IN the early days of motoring high speed was more of an adventure than is the case today because it had to be accomplished on dubious tyres and with very mediocre means of pulling up quickly if an emergency occurred. There stands to this day beside the long straight French road from Nonancourt to Evreux a memorial to Paul Zuccarelli, who was killed when the Peugeot racing car he was testing in preparation for the 1913 French Grand Prix hit a farm cart which emerged unexpectedly from a side lane. This is the sort of accident which the scientists who work in Ferodo's modern Research Centre at Chapel-en-le-Frith find hard to understand, and the stone which signifies the sad passing of this great driver might equally form a monument to the amount of research work Ferodo have done since to ensure that motor cars, of all weights and speeds, have at least a sporting chance of pulling up before disaster strikes.
This matter of efficient braking is of the utmost importance to everyone who ventures to travel in a motor vehicle—or for that matter, in a train or aeroplane—and it is of particular concern to competition drivers, who know that present-day races and rallies are won or lost as much on braking as on speed and acceleration.
In earlier times linings for racing-car brakes were of the woven type but recently moulded linings, which can be much more easily " tailored " to particular requirements, have become prominent in the high-performance field, although woven linings are still used on some family cars. To overcome problems of fade the disc brake is now all but universal for racing cars and is coming into increasing use on the higher-performance, or heavier, production cars. The disc brake for automobile use was developed from the use of this form of friction brake on aircraft. It has brought fresh problems for the manufacturers of friction materials, but these have now been largely overcome, and intensive research continues. Nor is the disc brake entirely ideal in all respects. Retardation from low speeds can be poor unless the pads are servo applied, there have been difficuties of disc scoring, with consequent rapid wear of the pads, while it is well known that an effective parking brake has been difficult to arrange with the disc system. These are problems that have been mastered, or which are at least understood since disc brakes were introduced initially for racing and sports cars. Ferodo, for example, have developed a new pad material (Ferodo 421 which not only refuses to score the discs but which wears four times longer than the earlier material while having the required µ at modest pedal pressures. It is pleasing to know that this Ferodo 421 was developed first for racing ears, then used for rally cars, and is now available for high-performance production cars.
In this country we owe everything to Dunlop, Girling and Lockheed for the availability of automobile disc brakes. They have each had problems to overcome but all now provide automobile designers with extremely good means of fade-free retardation from high speeds.
Dunlop, introducing disc brakes based on their aircraft designs and adopting them for sports/racing in 1953 on Jaguar cars, discovered that circular pads in alloy housings resulted in a thermal expansion rate of one-thou, per 100°, so that the pads tended to stick-on alter the brakes had been released by the driver. They cured that by adopting square pads in different housings.
Girling found on one racing-car installation that heat from the disc, rising over their original vertical pad calipers, either warmed the brake fluid, resulting in " stiction," or else caused the fluid to boil, with loss of pedal pressure. The cure was to move the caliper mounting through 90°, which gave the required reduced working temperature.
Lockheed have had to produce disc brakes without infringing patents held by other makers, which posed problems of design as well as research but which in the end resulted in extremely satisfactory brakes. It is interesting that because the pad for a disc brake does not have to be formed to a curved lace the material is easier to handle and can have a greater density, which assists towards long life, quite apart from the fact that pads can be changed more quickly than shoes. Nevertheless, as with linings, this is an individual item of equipment and an enormous number of variants are necessary to meet the requirements of cost, durability, pedal- pressure factors, resistance to fade. etc., posed by manufacturers of vehicles as diverse as a GP car or a double-decker 'bus. Ferodo, for instance, have over 10,000 different shapes, sizes and types of friction linings in current production. Although the disc brake is superior to the drum brake from the viewpoint of resistance to fade, and the extent of its adoption for production cars can be assessed from one of the accompanying tables, some manufacturers still place their faith in drum brakes. In this respect Alfa Romeo achieve excellent results,using the ultimate form of drum brake, which is the turbo-finned alloy drum with cast-iron liner, of decent size, well cooled. These present no lining problems. Mercedes-Benz have adhered to drum brakes, incidentally using American linings on the front shoes, German linings on the rear-wheel shoes, but rumour suggests that, as Facel Vega did, they may go over to discs. Looking at brakes 'generally, it can be said that some of the best are found on the Sunbeam Rapier, using Lockheed discs on the front wheels, which are powerful, fade-free and not subject to variations in pedal travel. The present position can be summed up by saying that Italian designers plan four good brakes and build a car round them, British-design-teams think of the car first and then how to stop it, while American automobile manufacturers don't try to stop their cars at all, their duo-servo shoes being very sensitive to µ. It was to learn more about brake lining problems that I paid a visit to Ferodo Ltd. to talk to Syd Henson, the Competitions Manager and himself no mean rally driver. Hospitality was laid on and an inspection of the Ferodo Research Centre arranged by their efficient Publicity Manager, Mr. W. P. Howard.
Herbert Frood, founder of Ferodo Limited, first produced friction materials at Chapel-en-le-Frith in 1897 and, buying a Benz a few years later, came face to face with braking problems which have been a Ferodo concern ever since. Today Ferodo is the major industrial undertaking in this Derbyshire town, the 16-acre factory which employs some 3,000 workers and the splendid new £¾-million 2-acre Research Centre, which must be unique in all the World (it was opened in 1958 by His Royal Highness, Prince Philip, Duke of Edinburgh, K.G., whose intelligent interest is remembered vividly to this day) occupying one side of the stonewalled road out from Buxton, with Mr. Howard's offices in an old private house on the opposite side.
Although I was aware that this company supplies friction linings for every conceivable automotive and industrial purpose and makes its own resins, and that it has been in existence for over 60 years, I had little idea of its present magnitude or the amount of money it spends on research. However, it was with the application of Ferodo linings and pads to competition and high-performance cars with which I was primarily concerned, not with manufacturing processes, and Syd Henson told me plenty. It is significant that although Ferodo became noted after the war for the service it provided at races and rallies, when two mobile servicing vans were operated under A. H. Collinson, the advent of disc brakes has rendered this service superfluous, although it is still operated for motorcycle competitors—at one T.T. meeting alone 456 brake assemblies were relined, by three fitters and one supervisor.
Racing has taught Ferodo valuable lessons which have resulted in better brakes for ordinary motorists. For instance, originally linings of good anti-fade characteristics were more stable in low-friction forms and so drivers accepted the high pedal pressures involved. But the aforesaid disc-scoring trouble led to further research, which initially obviated this problem at the expense of shorter pad life under racing conditions. Finally, Ferodo developed their 421 pads, which give good results under all headings for competition motoring. Disc brakes still require servo actuation to lighten pedal pressures on ordinary cars, and in this connection the Clayton Dewandre "Mot-o-Vac" should prove a worthwhile component. Incidentally, Henson considers that rally cars are more difficult over brakes than G.P. cars, because they are heavier and shroud their brakes from the cool winds that blow. However, he sees the requirements for racing cars as follows :—
1. A reasonably high level of friction, in the region of 0.3 to 0.4
2. The ability to maintain this level of friction without any great variations over a wide range of temperatures from atmospheric up to possibly 1,500° F. This latter figure may seem abnormally high but, nevertheless, such temperatures are obtained on certain disc brake applications.
3. The lining must withstand these conditions for the full Grand Prix distance or, alternatively, for a 24-hour race such as Le Mans without wearing sufficiently to require a renewal within this distance or time.
4. It must operate against its mating surfaces without undue scoring or heat spotting, as both of these contribute to rapid lining wear.
5. It must possess a high mechanical strength.
6. For many applications it must be suitable for bonding to Steel, aluminium or manganese shoes.
7. It must possess good water repelling qualities.
In general, said Syd, lap speeds are a direct indication of how hard a race circuit will be on brakes, with Aintree and Monaco the exceptions that prove the rule. Aintree is the worst circuit of all, because of the hard braking that follows the 150-mph. approach to Tatt's Corner, followed by the need for short dabs on the pedal round the rest of the course that maintain temperature, the Aston Martin disc brakes reaching 850 to 875° C. The second worst circuit is Sebring. Monaco is tricky, because slow-speed dabs result in fade, but the wear factor isn't excessive. The Nurburgring, surprisingly, is not hard on brakes. Coming to individual problems set by cars the B.R.M. has suffered almost entirely from mechanical troubles but its single rear disc brake running at 1 1/2-times axle speed does develop temperatures around 850 to 900° C. The lightweight Lotus and Cooper cars present no worries, their disc temperatures being in the region of 450° C. The sports/racing Aston Martins wore out pads very quickly and it was for them that Ferodo 421 was developed. The front pads then wore only 26-thou, during the Goodwood T.T. 1959, practice included, and a further 16-thou. on the drive back to Feltham. The 3.4 Jaguar was a problem car, because little air got to the brakes; the change from disc to wire wheels reduces disc temperature only about 45° C., for instance. Ferodo 421 was the complete answer and the same material enabled the Le Mans-winning Ferrari not only to run the 24 hours without a change of pads but to finish with them so little affected that they would have lasted another 24-hour race. The Austin Healey used to require one or two changes of front pads in rallies like the Alpine and the Liege-Rome-Liege, but last year, on the latest Ferodo material, no pad changes were made during the Alpine and only the rear pads were changed, merely as a precaution, in winning last year's tough Liege-Rome-Liege Rally.
Incidentally, as an example of unexpected troubles which can arise, a worn pad, while providing still-efficient braking in itself, can bring the piston so close to the hot disc that fluid boiling will commence. I asked Syd Henson how long it takes to change pads. He said that with the excellent quickly-detachable pads introduced by Girling and using a special tool to push back the pistons, both front brake pads have been changed in 17 seconds, after the front wheels have been removed. In a rally, two men can do the job in five minutes, inclusive of removing and replacing wheels.
The lessons of racing and rallies have led to immensely improved brakes for normal cars and Alfa Romeo and Maserati are using Ferodo MZ41 linings as used for racing on their production cars. In winning his second World Championship Jack Brabharn used a Borg & Beck clutch in his Cooper, the Ferodo sintered metal plates of which ran the entire 1960 season without being changed.
Today only two British brake lining manufacturers support motor racing and, a few foreign makes excepted, only three makes of linings are used in rallies. In the last Coronation Safari Ferodo was on 92% of the entry and at Riverside all but five of the starters in the American G.P. relied on Ferodo.
Testing and research at Chapel-en-le-Frith can be said to be divided into two classes: mathematical calculation and laboratory tests, and practical tests on road and test track and in international rallies. Although the mathematical assessments are almost foolproof, Ferodo find it very beneficial to confirm theoretical and laboratory results by hard driving on the road. They maintain a comprehensive test fleet, many different vehicles being driven, often over standard test routes, the cars ranging from representative small cars with Girling and Lockheed brakes, through larger family cars, to fast cars with drum and disc braking systems. Problem cars with special brake complaints are naturally included, the fleet averaging some 12 or 14 cars. Final tests are done at M.I.R.A. but Ferodo have their own test track, in the form of a resurfaced ex-quarry tramway, a mile from the factory. Although this has only a mild downgrade, it does enable tests to be conducted in privacy. Here,too, by a light-ray apparatus in conjunction with marks on the road, speedometers are calibrated at 30 m.p.h., so that accurate braking data can be recorded from this speed. Syd Henson also has a local test route in the Derbyshire dales, where, after warming up the brakes by artificial applications, he can try them for fade on a steeply descending, twisty hill, ending in a final straight of 1 in 5. We went out on this route in a heavily-laden Austin A40 and after Syd Henson had given it " the treatment " it came to rest willingly with very little smell of hot brakes which would have proved eminently satisfactory to the rally boys. The linings were Ferodo UG9/51.
It must be remembered that most of Ferodo's research is done for the brake manufacturers, rather than the car manufacturers who order brakes and expect them to work! A year before Ford announced disc front brakes as an optional extra Ferodo had a Ford Zodiac so equipped on exhaustive test. A disease known as "early morning sharpness " is sometimes experienced with the otherwise very efficient moulded linings; so cars in the Ferodo test fleet are braked from 10 m.p.h. at varying pedal pressures after standing in the open all night and a record is kept of how different weather conditions, etc., affect retardation. Syd Henson, apart from his main task of looking after competition drivers, has done a great deal of valuable research into braking problems, which he sees in the light of the hardest possible driving conditions. He evolved his own test apparatus, at first a simple counter contained in a car's cubby-hole to record how many times a rally driver used his brakes, then four such counters to tell how many brake applications were made, respectively, at 20, 40, 60 lb. and higher pedal pressures-these short circuited at the height of an Alpine Rally, but computed a total of 24,000 brake applications. In the 1955 Tulip Rally the percentage of braking to driving time was measured; 9% of the total rally driving was occupied in retarding the car, equal to an average of three stops of three seconds' duration per mile!
By 1959 a truly elaborate test set was fitted to an Austin A105 competing in the Monte Carlo Rally and, at the expense of running the battery fiat in the parc ferme, it gave the extremely interesting data shown in the table below.
These tests, apart from giving general data of great value, enable Henson to judge what sort of braking conditions will be experienced in a particular competition event. Amongst more general road tests, Ferodo have sent a coach to the Alps in the hands of drivers of widely varying ability and have conducted tests with Triumph TR3 and Bristol ears in the Alps and the Lake District. Just how far they look ahead is evident when you visit the splendidly equipped Research Centre. Space precludes any attempt at a description of the many fascinating experiments that are conducted in this beautifully-planned modern building. Suffice it to say that it must be quite unique; from the Weissenberg goniometer for recording the diffraction of X-rays by chrysotile asbestos, to chromatographic apparatus for separating complex mixtures, and the falling sphere viscometers for the control of experimental resin manufacture, to tiny test sets for simple measurement of friction, to the ten test machines in the lofty, spotlessly-clean Test House, Ferodo have the means for finding all the answers.
It is for this reason that motorists can be quite sure that Ferodo know which are the best linings for use in any production car; ordinary users should abide by their service station or garage recommendations and not ask for advanced or still-experimental types of linings, as racing and rally drivers find it permissible to do. The test machines can simulate any type or degree of braking in automatic sequence, recording the results on graphs; when I was there Sunbeam Rapier disc pads were going through a fade-resistance trial and Jaguar disc pads to a destruction test. It was on the largest of these machines that one of the special 16 ⅜ in. x 1 in. Girling disc brakes with six pairs of Ferodo pads to give a 78 sq. in. rubbing area for Donald Campbell's Bluebird car were tested. A dynamometer with 16 flywheels weighing a total of 6,800 lb. was run for half an hour until it produced 7-million ft./lb. energy at 2,600 r.p.m. The brake brought the test rig to rest in 32 seconds! Campbell was able to sit in a dummy cockpit and apply a pedal to see for himself that Girling + Ferodo would stop Bluebird from more than 400 m.p.h. and also to decide the pedal pressure best suited to his requirements.
During these tests the pad temperatures reached the fantastic figure of 2,200° F. and the disc glowed red, then yellow, at 1,600° F., as smoke and flames poured from the rig. But the pads, of commercial material but specially strengthened (they had been developed since October 1959 by a 15-man research team) stood up perfectly.
It is very nice to be able to state that these experiments encouraged Ferodo to apply this material to various industrial uses, again with complete success, a striking example of the value to Industry of such ventures as Donald Campbell's. The present holder of the Land Speed Record, the late John Cobb's Railton Mobil, and the previous holder, George Eyston's Thunderbolt, were retarded by Ferodo.
It can safely be said that if Ferodo cannot stop your car, no-one else anywhere in the World will be able to do so!—W. B.