The first Grand Prix, which was held at Magny-Cours, France, in the year 1906, presented a real challenge not only for automobile manufacturers but for tyre manufacturers as well. Since the 1200km hot dusty course caused numerous punctures, it put a strain on drivers as they had to replace tyres themselves, which was a painfully laborious process. An advertisement of the time projected it to be as easy as child's play but the truth was far from it. Thus Michelin's offer of the new technical innovation of completely detachable wheels amazed spectators, specially the performance of Ferenic Sziz who won the race at an average speed of over 101kmph on a Renault engined car. The key to Sziz's victory could be attributed to the fact that he managed to change a tyre in three minutes flat with these detachable wheels. Michelin also made history when out of the 34 cars which started only 11 finished, in which the first, second, fifth, sixth and eighth were all on these wheels.

Yet these wheels were a far cry from the wheels of today. Those days t raditional carriage wheels and wire-spoke steel wheels developed for the bicycle were alternatives available for automobiles. The three types of modern wheels are of pressed steel, wire-spoke wheels and light-alloy casting wheels. The pressed wheels are light, strong, stiff and resistant to accidental damage. They require negligible maintenance and are only inferior to alloy wheels on one count; they are heavier. Over 90 per cent vehicle manufacturers use such wheels, as they are easy to produce and cheap to manufacture in large quantities. Steel wheels are made from two pressings. The inset distance and rim profile are varied to suit the car manufacturer's requirements. The flange profile, indicated by letters J, K, JJ, JK, or B in the specification, is designed to comply with the tyre bead profile
Though I have already written about problems caused by using an incorrect flange type as well as the wrong width I repeat that it is of vital importance that correct width be maintained in relation to the tyre size as this is the factor responsible for the handling characteristics of a car. A rim too narrow in relation to the tyre width, for example, will allow the tyre to distort excessively sideways under fast cornering. On the other hand, unduly wide rims on an ordinary car tend to give rather a harsh ride because the sidewalls have not enough curvature to make them flex over road irregularities.

The earliest type of wheels were of the wire-spoke variety. They were light yet strong as they not only had to withstand the weight of the car but also forces of acceleration, braking and cornering. Normally all wheels are subjected to extreme loads and stress even in normal road use as during cornering they have to combat combined forces of braking and acceleration. Thus all loads on the wheel are transmitted from the rim to the hub by the spokes. These spokes were made of steel as they had to be stronger in tension than in compression. Spokes individually have little resistance to bending stresses, so they had to be laced in a complex crisscross pattern, ensuring that the load fed into a wheel was evenly distributed among the adequate number of spokes, thus converting the wheel to a tensile load similar to a pulling load rather than subjecting it to a pressing or bending load.

Assembling a wire-spoke wheel is a skilled operation, as each spoke has to be individually hooked at one end of the hub while its other end is pushed through a hole in the wheel rim, where a tapered nut also called as a nipple is screwed down pulling the spoke tight. If a spoke is too loose or too tight the rim that is relatively flimsy will distort. This labour intensified manufacture could be justified in the early days when the alternatives available were not so strong or light, but today such wheels are expensive because of their complicated construction. Such wheels are traditionally associated with vintage sport cars and racing cars, but strictly speaking have little justification today from an engineering point of view. Moreover the pierced rim of a wire wheel makes it impossible to fit tubeless tyres as they require airtight rims.

For steering control the wheels must be of rigid construction. With a pressed steel rim the 'spoke' portion is usually of near-conical shape for extra lateral stiffness. This proved to be of great disadvantage in the earlier designs as the disc had to be liberally perforated to allow the passage of cooling air to the brake drums, thus by piercing holes in the disc weakened it. The wheel manufacturers turned this to an advantage by using a slightly more expensive technique. The holes were swaged, which means that their edges were turned smoothly inwards, thus actually increasing the strength of the wheels. Today all wheel manufacturers use swaging technique as standard on their pressed wheels.

The third variant is light-alloy casting wheels which are generally meant to impress and essential quality and advantage is ignored. Alloys have the main advantage of being lighter than the other types of rims, but with use of a combination of aluminum and magnesium alloys have a thicker flange section, which promotes stiffness and distribute stresses over a wider area. This allows wider tyres to be fitted, which improves road-holding ability especially on corners and is one of the main reasons for their use on some sport cars. Light alloys are also good conductors of heat and thus allow heat generated by brakes and tyres to disperse quicker. They react badly to salt spray and must be checked regularly for corrosion. I shall focus on alloy wheels in future but now dwell on how wheels are mounted and problems regarding the same. The most common type of wheel mounting consists of either four or five threaded studs equally spaced in a circle around the hub flange. These studs pass through holes in the wheel, which is secured by nuts screwed on to the studs. The holes through which the studs pass are not simply pierced through but the area around each hole is pressed out to form a tapered seating which ensures a corresponding tight fit. Each wheel sits on a position which is centrally located on the hub and is called the pitch circle diameter (PCD) of the wheel. The hub diameter is known as the bore diameter.

Sometimes problems occur when a wheel with an incorrect pitch circle diameter is fitted, as my case study shows.