Formula One Trend of Design

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Wheel Fixings

For many years racing car wheels and fixings were almost universal, in the use of a splined hub and wheel and a threaded “knock-off’ eared hub-nut. The hub had fine external splines, while the wheel had similar internal splines, the one sliding over the other with the drive or braking being taken by the interlocking of the male and female splines. The end of the hub was threaded and a hub-nut, with a tapered mating face, was screwed on to lock the wheel in place. For ease of removal or tightening the hub-nut had two or three ears which could be hit with a copper hammer. Invariably the wheels were of the wire-spoke variety and this arrangement held sway until the advent of the cast-alloy wheel, which brought with it new thinking in methods of fixing and of transmitting the drive. It took a long time for the conventional wire-spoke wheel with splined hub to disappear from the Grand Prix car, even though the lead was set by cars such as Connaught and Cooper-Bristol as long ago as 1952. It was not until the doldrums of the 1 1/2-litre Formula in 1961-65 that the old-fashioned wire wheel and splined hub finally disappeared, this being caused by the search for weight-saving and the fact that tyres did not wear out and wheel changing was not an important factor in racing. This resulted in various forms of cast-alloy wheel being firmly fixed to the hub by five or six threaded studs and nuts.

As the 3-litre Formula developed and tyres became more significant the necessity for quickly removable wheels returned and the eared hub-nut re-appeared, but by now tyre and rim widths had grown enormously and with the hub-nut buried within the wheel it soon became impossible to wield a copper hammer on them so the pneumatic spanner was developed and the hub-nut became exactly that; a hexagonal headed nut tightened or loosened with the aid of a power-driven box spanner, the power coming from a reversible compressed air motor fed by flexible hose from an air bottle.

Today the basic principles of wheels and hubs in Formula One are universal but there is great variation in the details. The torque to be transmitted between wheel and hub, whether for drive or braking, is taken through a number of small locating pins and the wheel is held onto those pins by a single central nut, but that is as far as universality goes, though the use of cast alloy wheels is universal. There are three basic methods in use among the Formula One teams, the long thin stud with small nut bearing on a seating washer, the tubular axle shaft using a medium-sized hexagonal nut with integral tapered seat, and the very large diameter tubular axle shaft with very thin nut.

The solid stud attachment was first introduced by Cosworth on their 4-wheel drive car, in conjunction with cast alloy wheels using thick spokes, and Robin Herd took this design with him when he founded March Engineering in 1970. Since then this type of fixing has been quite popular and today is used by Lotus, Tyrrell, ATS, Wolf and Ensign. The medium-sized tubular stub axle is a logical development from the old-fashioned splined hub, and is used by Renault, Brabham, McLaren, Fittipaldi (on the front only), Shadow, Ligier, Williams and Arrows. The very large tubular stub axle is used by Ferrari in conjunction with large diameter ball races, and Fittipaldi use a similar system on the rear of their F6A. Although numerous teams may use the same principles there are still variations on details such as the number of driving pins and also on the safety-clips used once the retaining nut is tightened. There is agreement, however, among the five designs using the solid stud fixing; as mentioned, these are Lotus, Tyrrell, ATS, Wolf and Ensign and they all use six driving pins screwed into the hub with mating holes cast in the wheel centre. Once the wheel is on the driving pins a small nut is tightened up against a tapered distance piece and an R-shaped spring clip is inserted through a hole in the end of the retaining stud. These clips are not expected to restrain the nut if it should come loose, but are fitted as a check for the mechanic that he has tightened the wheel nut. During practice or preparation when a wheel might be removed for some considerable time each team has its own method of security-checking. Some put those R-shaped clips on the spokes of the steering wheel, others clip them onto the seat-belts, some clip them onto the brake cooling ducts or onto the nose fins, but always somewhere they will not be overlooked or forgotten, and in that way wheel nuts do not become overlooked for a final tighten.

Where the medium-sized (approximately 2 1/2″ diameter) tubular stub axles are used there is not only a difference of opinion on the number of driving pins but also on their layout. Also on the size of the nut there are variations and on the retaining clip. Brabham, McLaren and Ligier use four driving pins front and rear, while Renault and Fittipaldi use six driving pins. Williams use four pins at the front and six at the rear, and Shadow and Arrows use three pins at the front and six pins at the rear. Among this collection Williams are unique in having the front driving pins screwed into the wheel casting, these four pins locating in a circle of twenty holes in the brake disc, so that the wheel can be put on in any of five positions, whereas with the more normal arrangement of the pins being screwed into the disc or hub the wheel can only go on in one position as there is not room in the wheel centre for more than the same number of holes as there are pins. At the moment the rear wheels on the Williams are conventional, with the six pins screwed into the hub, but the reversed layout will no doubt be used on the FW08. FittipaIdi, Shadow and Williams colour their hub-nuts for ease of recognition, green for the right-hand hubs and red for the left-hand ones. Of this group Ligier show a slight difference in using a large diameter nut. Apart from McLaren they all use some form of scissor-action retaining clip which is inserted into the hollow stub axle so that the ends protrude outwards through holes drilled radially through the tube. McLaren use a complex form of R-shaped clip.

Ferrari use a tubular stub axle of some five inches diameter and the large thin nut locks up on a tapered seat without any form of safety-clip, though Fittipaldi, who use this large type of stub axle on the rear only, use a scissor-movement clip inside the tubular shaft.

What actually determines the method of attaching the wheel to the hub depends largely on the designer’s ideas on hub bearings and hub construction, the decision as to which of the three forms to use depending on the initial design of the hub carrier, the type of ball or roller-race used and the safety factor to which the designer is working. The solid pin layout is simpler and probably lighter, but suffers in so much as solid pins have been known to shear and then the wheel parts company with the hub. Breakage of a tubular hub shaft is virtually unknown. — D.S J.

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