Once the rigid, vintage type, rear axle had been done away with where the rear brakes were naturally on the ends of the axle tubes, some thoughts began to be given to the rear brakes on racing cars. Independent rear suspensions gave way to the de Dion layout and then sophisticated independent rear suspension began to take over. This final trend came with a great interest on overall weight and also of unsprung weight and the great mass of a rear brake pounding up and down with the wheel and the hub was considered a bad thing. Mounting the brakes inboard, on each side of the final drive housing became the obvious thing, and some designers had achieved this with de Dion layouts. In the present 3-litre Formula the Hewland transmission was almost universally used and when the demand was sufficient Mike Hewland modified his production racing transmission to accommodate inboard mounting of the calipers and discs, so all at once inboard rear brakes became the fashionable thing.
In recent years tyre characteristics and suspension thinking has led to a belief that unsprung weight is not all that important. Prior to this it was the ratio of sprung weight to unsprung weight that was all-important, but this factor is no longer number one priority. One of the problems with inboard-mounted rear brakes is dissipating the heat that is generated when they are working. Loosely speaking people talk about keeping the brakes cool, but what they really mean is getting rid of the heat that is being generated. If a brake does a given amount of work in stopping the car then a given amount of heat is generated, and this heat must be got rid of before it soaks into the brake components and surrounding parts of the car. You often see large scoops and ducts leading air into brakes with little or no way for it to get out. You cannot feed air into anywhere unless there is a way out for it. Inboard rear brakes have often been the cause of the failure of other components, such as drive-shaft universal joints, gearbox bearings and shock-absorbers, simply because the heat being generated under braking is allowed to soak into those components, affecting lubrication, grease seals and fluids.
With the current advent of under-car airflow everyone is aiming to give the air the easiest flow-path out through the back of the car and one of the obstructions on many cars has been the rear brakes. This was a good incentive when designing an entirely new car to mount the rear brakes outboard on the hub carriers. Brake pad design and quality is such that rear brake temperatures can now be kept within reasonable limits no matter where they are located, so the simplest thing was to bury the whole lot within the rear wheels, well out of the air-stream. Gordon Murray did this on the Brabham BT48, and he was followed by Renault on their 1979 cars and by Patrick Head on the Williams FW07 cars. None of them were worried about the unsprung weight, as modern tyres need a certain amount of static weight on them and the disc brake assembly of today is not an unduly heavy component. Chapman retained inboard mountings on the Lotus 80, but before long has redesigned the layout and moved the brakes outboard, and Harvey Postlethwaite mounted his brakes outboard on the Wolf WR9, whereas they had been inboard on the WR8. The latest modifications to the Shadow DN9 series has seen the rear brakes moved outboard.
Those designers who more or less followed the lead of the Lotus 79 left the brakes inboard, as on the Tyrrell 009, the Ligier JS11, the Ensign, the Fittipaldi, the ATS, the McLaren M28 and M29 and even the unusual Arrows A2. The T4 Ferrari was a different case, for the transmission and brake layout followed the T3 and the rear brake discs are buried deep within the mechanism.
While there are two distinct schools of thought on the position of the rear brakes, either inboard on each side of the final drive housing, or outboard beyond the hub carrier, there are many variations on the system and number of calipers and pads that are used. Of the outboard mountings the Brabham and the Shadow use a single caliper, while Lotus, Renault, Wolf and Williams use two calipers, one in front of the hub and one behind. There is similar variation among those adhering to inboard mountings, Tyrrell, Ferrari, and Ligier using a single caliper but of the two-pot variety which means it has four brake pads, while Fittipaldi, Ensign and Arrows use two calipers. Everyone uses ventilated discs, which is to say the disc is provided with radial slots which lead into an annulus around the mounting hub and air is fed into this annulus so that it centrifuges radially out through the disc. Ligier use drilled discs while the others use discs with radial slots cut in them to disperse brake pad dust.
It is true to say that no two Formula One cars have identical rear brakes, even the pipe layouts vary according to the whims of the detail designers. Renault are unusual in that the inner caliper of their twin-caliper layout, is part of the hub casting, an idea introduced by Lotus some years ago. Some designers use Lockheed calipers, others use Girling and the majority use Ferodo brake pads. From brakes being universally mounted inboard, the trend now is to mount them outboard in the interests of getting them out of the under-car air-flow, so we have gone the full circle. — D.S.J.
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The Isle of Man Hill-Climb
One tends to think of the roads in the Isle of Man only being closed for the TT motorcycle races and Manx Rally, but they can be closed for many other things as well (oh happy land!). The Longton & District Motor Club, in the NW of England cross over to the island and have a section of the motorcycle circuit closed for a hill-climb. It runs the reverse way of the course, from Hillberry up to Brandish Corner, then to the famous Creg-ny-Baa and on up to Kate’s Cottage, a distance of 2.15 miles of very fast motoring.
As part of the IoM Millennium Year the Club are putting on a match race between Brian Redman in a racing car and Phil Read on a motorcycle, the actual vehicles yet to be decided. This is in addition to all the usual hill-climb classes with over 80 entries. A three-day special holiday weekend is offered for spectators and details can be obtained from Mrs. G. Nicholson, 17 Lansdown Hill, Fulwood, Preston PR2 3WD.
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The Things They Say . . .
“. . . the 90, 105 and 100 models . . . were outstandingly successful in sports car races and in rallies between 1930 and 1935” – a contemporary, reporting on the revival of the marque Talbot by the french combine that now owns Chrysler UK. But how many races and rallies did these Roesch Talbots win outright.