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RACING AND SPORTS CAR CHASSIS DESIGN PDF

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RACING. AND. SPORTS CAR. CHASSIS. DESIGN. Michael Costin and David for the more serious student of design are contained in appendices at the. Racing Sports Car Chassis Design - - Free ebook download as PDF File .pdf), Text File .txt) or read book online for free. Download PDF Racing and Sports Car Chassis Design, PDF Download Racing and Sports Car Chassis Design, Download Racing and Sports.

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Published in: Full Name Comment goes here. Are you sure you want to Yes No. Be the first to like this. No Downloads. Views Total views. Actions Shares. This consists of four tubes, of relatively large diameter, linked by a series of unbraced bulkheads I the top right-hand member also acts as a water pipe.

Accessibility is hardly likely to be as good as on a twin tube car, but this depends largely on the design. Durability depends mainly on weight, but even a heavily-constructed chassis of this type is more liable to structural failure than a well-designed lightweight space frame because of the bending loads taken by the welded joints.

Chassis of this type can also be very difficult to repair after even quite slight impacts, owing to the fact that loads are transmitted throughout the frame rather than restricted to a small area, as is often the case with a space frame.

Racing Sports Car Chassis Design - | Suspension (Vehicle) | Transmission (Mechanics)

Construction costs are similar to those for a space frame, but unless the chassis is made to wide manufacturing tolerances and the brackets are fitted afterwards, irrespective of their position, it is sometimes extremely difficult to make the chassis and the components fit together.

Experience generally shows that it is very difficult to keep a chassis of this type dimensionally accurate during manufacture. In the multi-tube category can be included many chassis which are normally described as being of the space frame type but which are, in fact, merely four-rail chassis with diagonal bracing where convenient. Con- versely, as very few true space frames have ever been made, it is necessary to consider in this category many chassis which come near to the ideal but with some compromise in important areas.

Of these, the cockpit of a sports car is usually the most critical area and the torsional stiffness of almost all space frames could be improved by as much as per cent by running a diagonal across the top of this bay. In general, uniform stiffness is essential for a proper structure, and if one part is too stiff the concentration of loads and deflection at one point may lead to fatigne failure. Although in some respects the multi-tubular frame is an advance on the twin tube chassis, it is not to be encouraged, as it is neither simple nor efficient.

The Cooper racing car may be cited as the exception which proves the rule. Space frames See fig. Unitary construction may be superior in some instances but there are many factors against it, as will be shown later.

As regards the space frame, it is difficult to imagine a chassis of this type having adequate torsional rigidity without automatically having ample rigidity in bending. However, the criterion of chassis design-and in fact the primary function of a high-performance chassis-is torsional rigidity.

In a sports car chassis it is almost impossible to arrive at a true, complete structure because of the necessity to compromise. The best example of a space frame chassis from the point of view of torsional rigidity would be a square-section rectangular box, with ends, sides, top and bottom trianl! S OF CHASSIS type of chassis, but at the same time it would be entirely impractical for automotive applications, particularly from the point of view of accessi- bility.

Thus a chassis has to be split into bays, preferably two, but normally compromise creeps in, making three or four bays simpler from the point of view of localising the effects of the compromise. However, a major advan- tage of the space frame is that, as the very best use is being made of the material, the minimum of material is required.

In over-all car design, accessibility is almost as important a factor as chassis rigidity, because it is essential to be able to service the car and to get all components into or out of it with the minimum of delay.

If a chassis member-usually a diagonal- interferes with this, it can be made removable. In some cases the engine can be used as a chassis member but this is to be discouraged because of difficulty with engine vibration and the need for rigid mountings.

Among other problems in this department are complication of the exhaust system, owing to the need to avoid chassis members, and the difficulty of accom- modating carburettors. In addition, the fitting of the rear axle is made more difficult by a multiplicity of tubes, especially if independent or de Dion- type suspension is used, when the drive unit is mounted centrally and maintenance work must be carried out at arm's length from above, behind or at one side.

A well-made space frame chassis should be very durable. The only danger of failure due to long service is likely to come from within the tubes because of internal rusting and corrosion.

This can be avoided by suitably treating and sealing the insides of tubes, although pop-rivet holes sometimes confuse the issue in this case. Impact resistance should be good in the case of minor bumps, as damage should be limited to the bay receiving the blow. Major impacts are absorbed progressively, each bay taking part of the strain until it can no longer accommodate the rapidly rising load.

Thus in the case of a high-speed collision, although the car may be extensively damaged, the fact that it slows down progressively often minimises injuries to the driver. From the production point of view the space frame is probably the most expensive tubular chassis to make, because of the number of tubes used and the amount of welding involved. But it is undoubtedly the most efficient. Unitary Construction See figs. This category includes what are basically sheet metal platform chassis supplemented by superstructure which also provides stiffness.

In large quantity production this is probably the best method of construction. Smaller scale production should be economically possible using resin-bonded glass-fibre, but this type of construction is in a very early stage of development. In the course of design, each panel or bay of a unitary construction chassis must be stabilised to carry out the function of transferring loads.

The simplest way to achieve this would be to use a large, round section tube with the ends blanked off. Such complications as holes for the doors, boot and bonnet cause this type of chassis to depart even further from the ultimate, while practical considerations generally make it necessary for the bodywork to be tapered off at each end.

Any operation on a tube, such as tapering it or cutting holes in it, must have adverse effects on it structurally. With flexing, holes crossing load paths change their shape. Since there must be holes, despite the reduction in efficiency which they cause, the design must incorporate additional frames and bulkheads to stabilise the surrounding areas.

The use of this type of chassis would seem to offer many advantages, to judge from the developments carried out in recent years in aircraft manu- facture. Such a structure can be made very stiff and extremely light-an essential feature in aircraft design-and in a car of this type 30 gauge material would probably be quite adequate. It is perhaps not commonly known that the engines of the De Havilland Comet are hung in stabilised 26 gauge stainless steel.

The load capacity of a unitary construction chassis in bending should be extremely good, because bending loads are resolved into pure tension and compression in the undertray and roof, to which type of loads these areas are ideally suited. Such a chassis should also be very good from the torsional point of view, but in practice everything depends on general and detail design around the apertures.

This is particularly true in the case of an open car, which lacks the diagonal bracing provided in a closed car by the roof. Even here, however, with careful design adequate torsional stiffness should be available.

Weight should be lower than for any equivalent chassis because, with good design, a far greater proportion of the weight of the material can be made to carry loads than is the case with a separate chassis and body. In general, a unitary construction design should be stiffer than an equivalent tubular space frame and body for the same weight, or lighter for similar stiffness. Accessibility depends on the design, and this in tum depends on the degree of compromise reached between chassis stiffness and practicability.

Durability depends on operating conditions but should be good, all other things being equal, while accident damage should be localised-given good design-making the cost of repairs fairly low. In the choice of materials, the most important factors to bear in mind are fitness for purpose and cost.

As has been mentioned in Chapter II, the type of production envisaged has a considerable influence on the type of chassis which can be used for any given car-and therefore on the materials which can be utilised.

Unitary construction in pressed metal would be ideal for many limited production cars, but the cost of tooling renders it impractical. Unitary construction in glass-fibre or wood is more feasible in such cases, but both materials are relatively so new in this application that the use of separate chassis and bodies remains the simplest solution in the majority of instances.

Despite the recent trend towards monocoques, there still seems to be a considerable future for tubular steel chassis. For such purposes a wide variety of alloy steel tubing is available, ranging from high quality chrome molybdenum and nickel chrome steel to the ordinary mild steel used by the majority of specialist sports and racing car constructors. Each of the different types has its own special properties and uses. Twenty-five ton mild steel is quite suitable for welded tubular structures of the space frame type, but some manufacturers use a material which approximates to aircraft T45 specification, a manganese steel alloy which is particularly suitable for welding.

Chrome molybdenum steel is generally used for twin tube chassis, but in this case manganese steel would possibly be even better, because it retains its physical properties during gas welding much better than do other steels. If the higher quality ton steels-chrome molybdenum and nickel chrome-are used, electric welding becomes almost essential. At this point it might be appropriate to digress a little to consider the respective merits of welding and brazing.

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Both are widely used, and recent developments in nickel bronze welding and manganese bronze welding techniques-together with improvements in the composition of the basic material-have resulted in joints becoming superior in performance to the original welded joint.

In this context it is important that bronze welding is not confused with brazing. Welding Welding is a method of joining two steel tubes together by heating them to melting point locally with an oxyacetylene flame, forming a weld fillet or puddle, and keeping this constant by adding filler rod as necessary. In general a similar method is followed for nickel bronze or manganese bronze welding, but these alloys have a much narrower heat range and greater care must be taken with them, as insufficient heat will cut down penetration and therefore the strength of the joint, whereas overheating is equally bad due to intergranular penetration of the filler rod into the surface of the steel.

This not only makes a weak joint, but at the same time considerably weakens the affected steel component. It is difficult to detect a weakness caused in this way and thus the strength of the chassis depends largely on the skill of the operator. Brazing Brazing consists of building up general heat, of a lower order than that required for welding, and applying filler rod in a stroking manner.

As soon as the latter runs into the joints the area can be considered per cent treated. Very similar to brazing is silver soldering, which does much the same job at lower temperatures.

In this case extreme cleanliness and adequate coverage of flux is absolutely essential. Whichever method of making joints is employed, the strength and life of the chassis are largely dependent on the cleanliness of the parts to be joined and the general preparation which is carried out before each stage of the work is commenced. In conjunction with a space frame type chassis it is often desirable to use the undertray and other body members as load carrying panels. For such purposes clad materials-generally high-performance copper-based alloys, with high purity cladding either side for protection-are usually the most suitable.

These are normally secured to the basic chassis structure by pop rivets. For this purpose, and also for general body shape panels, it is also possible to use various alumiuium alloys.

These fall into two different classes: It is also possible to use sheet Elektron magnesium alloy in such cases. This material has the great advantage that it weighs approxinIately one- third less than comparable aluminium alloys. Elektron is also widely used on specialist high-performance cars in the form of castings. With any type of tubular chassis it is normally necessary to use an entirely separate body, but in unitary construction cars the two purposes can con- veniently be combined.

As mentioned in the previous chapter, tooling costs make pressed metal structures unecono- mical unless at least can be sold, and this leaves only glass-fibre and wood, of materials currently in use. As is shown by the Lotus Elite, glass- fibre can be used successfully with very little metal reinforcement, but the problems involved almost outweigh any advantages which are gained and it is not inconceivable that such a car could be made more economically with a separate chassis without any adverse effects on its over-all perform- ance.

Even glass-fibre involves tooling costs in the form of moulds injection moulding would seem to be the solution here, but it in fact raises costs into the pressed steel structure range and for even smaller scale production a possible answer is wood, as instanced by the Marcos. Here plywood is combined with glass-fibre for some of the curved panels and the result is an extremely stiff and durable structure.

Both glass-fibre and wood have the advantages that they do not suffer from rust or cor- rosion, and in addition they are not subject to fatigue. Modem wood treatments render fears about beetles completely irrelevant in this con- nection, and should also obviate the risk of dry rot I Three-dimensional curves are extremely costly to make in wood, but this can normally be over- come by using glass-fibre for relatively small areas.

Glass-fibre--resin-bonded glass-fibre to give it its full name-is still a comparatively new material, and very little is generally known about its properties or method of construction. The raw materials involved are the glass-fibre" mat" itself, in the form of strands or thin sheets, and the resin which is employed to bond the fibres together.

Successive layers of glass mat and resin-when set hard-form a very tough and resilient material. The ultimate in both strength and lightness is provided by two thin layers of glass-fibre separated by a layer of plastic foam. The process of setting, or curing as it is generally known, is the most critical.

Most resins-particularly polyester, the one most commonly used It is normally necessary to use heat to reduce curing time, and this is liable to increase the amount of distortion. Shape is provided by the use of a mould made on a wood, plaster or metal pattern-which in many cases is a hand-made prototype car.

In this mould the required amount of glass-fibre is impregnated with resin and cured. The chief disadvantage of this method is that the reverse side always has a rough unfinished appearance which can only be avoided by match moulding-that is by lowering a male mould on to the female mould before curing in order to compress the material and provide a smooth finish on both sides. An alternative is to use two laminates bonded back to back-as on the Lotus Elite-but both these methods are rather too ela- borate and much too expensive for the small-quantity producer.

Unless great care is taken this can lead to small ripples on the surface- which are further exaggerated by shrinkage during the curing process- giving the car a characteristic" special-bodied" appearance. The ideal method, of course, is injection moulding, whereby sheets of glass-fibre are laid between male and female moulds into which resin is injected, the panel then being rapidly cured by electric elements incor- porated in the moulds.

Unfortunately, in order to withstand the pressures and temperatures involved, such moulds must be made out of metal- which makes them almost as expensive as the dies for pressed steel bodies.

This method also takes much longer than the normal steel stamping, but has been successfully used by General Motors on the body of the Chevrolet Corvette. In the future, however, it may be possible to make monlds of this type from synthetic materials and to inject both the resin and the glass- fibre filaments at the same time. Such a development would obviously bring glass-fibre into the true mass production range. Whatever type of chassis or body is used, it is normal for suspension linkages to be made of some form of steel, and in this case the choice is limited largely to the materials mentioned under this heading in connection with tubular chassis.

In the majority of cases ordinary mild steel is com- pletely adequate for wishbones, radius arms, de Dion tubes if used and most other forms of suspension linkage. Suspension uprights can either be steel fabrications or castings, and in the latter case the most suitable material is Elektron, on account of its excellent strength-to-weight ratio. For extremely small quantity production, however, fabrication from sheet steel is probably the best solution, and in fact the use of tubular or sheet steel throughout the car is strongly to be recommended if high quality and low cost are to be combined in the most satisfactory manner.

In such a case aluminium or glass-fibre bodywork is to be preferred, and in this instance it is interesting to note that several manufacturers currently make a single aluminium body for each new model they produce, using this as a pattern from which to make moulds for subsequent glass-fibre bodies. As long as production runs into double figures, it should be possible in this way to undercut the cost of making the bodies separately from aluminium. Specifications and properties of the most commonly used materials for chassis, bodies, suspension linkages and other components are included in Appendix II.

By definition, a true space frame is a complete structure in which all joints could be flexible without the chassis losing any of its stiffness there- by. This means that stiffness must not in any circumstances be imparted by putting bending loads into members at joints.

In fact joints should only be loaded in tension or compression. In addition to the complete chassis being a structure, every section should, in itself, be a complete structure.

As has already been mentioned, practical considerations require the chassis to be divided up into a number of bays. Should anyone of these be structurally inferior to the others the whole chassis will suffer as a result.

The first requisite in a chassis of this type is a balanced structure, as apart from being a space frame it is also a means of joining and reacting loads in all planes. Therefore it is extremely important that the over-all structure be borne in mind from the first stages of design. As has been emphasised earlier, the chassis must always be regarded as a means to an end and never as an end in itself.

Having established this, it is extremely difficult to discuss space frame principles without at the same time taking into account the purpose for which the car in question is being designed.

In general, after dividing space frames into two types-single-seater and two-seater- and bearing in mind the obvious differences between them, it is still possible to consider the two chassis as being basically similar from a structural point of view. The simpler case is obviously the single-seater. For a car of this type, the starting point of design is the location of the pick-up points for all the various items of equipment which must be con- nected to the chassis. The most important of these are front and rear suspension, steering gear, engine and transmission, seat, gear lever and pedals-and other heavy items such as fuel and oil tanks, radiator and batteries if carried.

Having decided upon the wheelbase and front and rear track of the car, the approximate frontal area and over-all shape, the next step is to plan out as nearly as possible the exact positions of all the main chassis tubes, placing them so as to obtain the largest possible section through the structure while providing location for all the major brackets.

However, although these drawings show the more desirable positions for brackets feeding suspension loads into the chassis, there may well be some overriding factor considered more important by the designer, such as unjustifiable aerodynamic disturbance or undesirabie effects on sus- pension geometry, which would make it better to have an inferior structure for the sake of a superior mechanism.

This is where compromise begins. In all cases chassis design must be completed before the choice of materials is made or work is begun. Design actually starts as a series of forces, which are later made into chassis tubes. As a series of lines on paper,. II Left The ideal method of feeding suspension loads into a chassis, through brackets which are on the same axes as the linkages involved.

Right By comparison with the diagram on the left this might be termed.. In practical terms, offsets of this nature represent the limits of acceptable compromise when other considerations prevent the use of the ideal layout. Using his experience he can decide which members should be made in relatively large section, thick- wall tube and which reqnire only light tUbing.

The beginner must either work out a complicated series of calculations-as shown in Appendix l - or follow the example of established constructors. For the current high- performance sports or racing car the majority of needs are met by mild steel tube in the following dimensions: For comparatively lightly stressed members i inch 18 gauge tube might prove to be quite adequate. All these dimensions, however, are dependent on the chassis being designed on space frame principles.

Ideally, to design a complete space frame starting from scratch, it is necessary to stress the whole chassis three-dimensionally. In practice, experienced designers are unlikely to attempt full stress calculations on any new chassis but rather to rely on experience and to put purity of structure second to convenience of construction.

When tackling design this way it is essential to know what compromise can be made without detracting from the over-all stiffness of the structure. If practical considerations demand it, poor engineering can be accepted- but only if the designer himself recognises it. An experienced man can design a satisfactory space frame- and one which in practical terms may be superior to an ideal structure-without recourse to calculations.

But the beginner can hardly expect to do the same thing, even if he attempts to copy the work of a major constructor. This was clearly shown in Formula Junior racing during Even the most experienced designer will probably use a scale model to check his ideas on vital points before com- mitting himself to the actual construction of the car. Studies of this nature must be purely qualitative, however, as it is not possible to work out loads on a scale model.

Much has been said and written in recent years about cars, particularly racing and sports cars, becoming too light. Experience has shown, however, that light weight is a major criterion of performance, particularly in terms of acceleration and roadholding.

In view of the weight restrictions now imposed in almost every sphere of international racing, it must be emphasised that chassis and suspellsion components should always be designed to be as light as possible, any weight which must be added being in the form of useful parts.

It should also be pointed out that parts of a chassis can be made too heavy, to the detriment of the structure as a whole as a result of distortion caused by built-in stresses.

For ultimate perfor- mance it is still a good maxim to design light and add weight where experience dictates. Whatever the chassis, the tubes of which it is composed must be suited to the loads which they are to carry. Ideally no tubes should be loaded in.

Racing Sports Car Chassis Design - 0837602963

That in the centre has been made into a structure by the introduction of a diagonal. On the right is shown a method of bracing a frame in which it is not possible to fit a normal diagonal.

In the case where an offset is required for mounting a vital component, the trend is to increase the diameter of the tube to give a greater section and avoid difficulty from compound loads.

And practical considerations-such as increasing the gauge of a tube which is to be used as a footrest, in order to allow for wear-must always be borne in mind, however complex the calculations which are carried out. In all chassis, and particularly single-seaters, the provision of space for the driver prevents full triangulation of the top frame of the driving bay.

This consideration alone makes the design of an ideal chassis almost impossible. However, various methods of external triangulation are possible, as shown by the Mercedes-Benz SL and the space frame Lister- Jaguar.

The principle in this case is to build up diagonally braced beams or.. It would also be possible to brace the top frame of the cockpit-at least on a single-seater-by means of a" perforated hoop" type structure as used for the scuttle bulkhead on some Lotus models.

The Lotus Mark 8 See fig. Very simple, extremely light and very stiff, this chassis- the only one of its type ever made-is still giving good service after six years of use, and this despite the fact that it is made up of 20 and 18 gauge tube.

As can be seen from the accompanying drawing, the primary structure is fully triangulated and therefore extremely stiff. It consists of two sections on either side of a central bulkhead, the forward section being triangular in plan view, the rear triangular in side elevation. Only nineteen members are used in its construction, and the total weight is 21 lb. All members are straight and there are no structural offsets. From a practical viewpoint, however, this chassis is open to a great deal of criticism.

It was designed as a pure structure, with little thought for the loads which were to be fed into it, and thus it was necessary to add to the ideal basic structure a number of less satisfactory secondary structures through which these loads could be engineered.

It has since been shown that it is far better to merge primary and secondary structures in the in- terests of a superior over-all chassis. In addition, practical experience soon showed that even the ideal basic layout had serious limitations from the point of view of maintenance.

As an instance of this, it was necessary to dismantle the engine in order to get it into or out of the chassis. Cylinder head, manifolds, oil pump, water pump, distributor, front mounting, starter and dynamo, all had to be removed before the engine would pass through the narrow opening in the top frame. Because of the disturbance involved this almost inevitably meant that the engine produced less power in the car than when it was built up on the test bench.

In addition, the use of stressed bodywork interfered seriously with the servicing of many smaller components. By contrast with the simplicity of the primary structure, the secondary structure necessary to feed suspension and other loads into the chassis is extremely complicated. The outer ends of this transverse member were designed to accom- modate the top eyes of the suspension unit.

Just inboard of these pick-ups are welded the two other members of the triangle, which converge to form pick-up points for the swing axle eyes at their apex near the undertray line. This triangular frame deals with the main front suspension loads. Suspension drag loads and brake torque reactions are taken out by radius arms located at a point approximately three-quarters of the way along the bottom chassis tubes; any consequent bending loads are taken out into the undertray by further tubes which run diagonally back towards the centre of the car, meeting the transverse bulkhead at the front of the under- tray section.

One of the aims of this design was to mount the engine in such a way that loads could be reacted directly through the front suspension-in fact to hang the engine on the front suspension. This led to the construction of an extremely complicated front engine mounting, which consists of a tubular pyramid of four i inch thick wall steel tubes picking up at various points on the front of the engine and converging to meet at a steel bush which acts as a housing for a Silent bloc-type bush.

This is supported with the axis of its mounting bolt in a fore-and-aft plane and passes through two vertical flanges of the top-hat section member on the centre line of the chassis. From the chassis viewpoint this is quite satisfactory, but special triangular brackets are necessary to avoid twisting of the steel sandwich plate at the various pick-ups around the front timing cover of the M.

The rear engine mounting is taken from the normal M.

As at the front, a secondary structure is necessary to take out rear suspension loads. Vertical loads are taken out at the apexes of the triangles which form the seat-back bulkhead and lateral loads are fed into the under- tray.

The differential unit, which also provides lateral location for the de Dion assembly, is located by four mountings, one above and one below on the centre line and one on each side. Loads from the latter are taken out into the side walls of the propeller shaft tunnel by means of steel brackets.

In practice this layout has given considerable trouble, as the passage of loads from extremely stiff brackets into 20 gauge aluminium leads to straining and eventual failure. Trouble has also been experienced with the complicated mountings for the transverse coil springs, which incorporate piston type shock absorbers as suspension linkages. Fore-and-aft suspension loads are taken out by parallel, horizontal arms into a vertical side frame member, located at the junction of the main side frame member and a secondary tube which comes forward to meet it from the seat-back bulk- head.

This member also helps to overcome a possible weakness in the shallow section of the chassis side frame immediately in front of the seats. The Lotus Mark 8 was the first sports car to feature fully aerodynamic bodywork, designed by Frank Costin and supported on the chassis by light alloy sheet bulkheads. Only the front section of the bodywork is removable, the remainder being riveted to the sheet alloy which supports it. The front body mounting consists of a tubular and sheet steel structure coming forwards from the front vertical member of the chassis and also incorporating the radiator mountings.

Like the Lotus it can be summed up as a virtually ideal primary structure, with somewhat less satisfactory secondary structures dealing with engine, suspension and transmission loads. In some ways it can also be compared with the Mercedes-Benz SL chassis, particularly in the way it achieves torsional stiffness of the cockpit section by means of external beams on either side of this bay. In over-all design, however, it is far superior to the Mercedes, particularly as the structure is much more of a unit and great pains have been taken to ensure continuous load paths.

It is also noteworthy that there is no weakening of the structure from a torsional point of view behind the rear axle line. Unfortunately, however, the purity of the structure illus- trated in fig.

It should also be remembered that the structure illustrated is incomplete due to the absence of the undertray and other sheet metal stiffening members. The full-length undertray is an essential part of the chassis, providing diagonal bracing of the entire bottom frame.

Adequate bending stiffness is imparted to the two side" beams" by the central Portal frame, which restrains any outward movement of the side members.

It also withstands torsional loads, in conjunction with the front and rear bulkheads, and all three combine with the very rigid side frames to produce an extremely stiff structure. One point on which the primary structure illustrated might be open to criticism is the use of long unbraced tubes in the side of the front bay. In practice, however, small diaphragms are fitted to provide stability at these points.

Mention of load paths has already been made in connection with this chassis, and in this context it is worthy of note that front suspension loads are taken out directly by the rear suspension, and vice versa.

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