It must have the same number of cylinders as the original. It must have the same number of valves per cylinder and the same method of valve operation as the original. The gearbox and differential casings must be as originally manufactured, and retained and fitted in their original positions. The ratios and other internals are free. Suspension must be of the same type and method of operation as that offered by the manufacturer for the vehicle.
Shock absorbers are free as to type, method of operation and position of location.
Wheel sizes are free but must all be of the same diameter, unless different diameters are fitted as standard by the manufacturer. Tyres marked with the words 'Racing Purposes Only', or similar wording are not allowed. Cross ply tyres are not allowed. Cars with tyres offered as manufacturers standard or optional fitting, of wider section or lower aspect ratio than shown above, may be eligible to use either those tyres, OR tyres conforming to the above criteria. The onus of proving eligibility to use non-complying tyres is the responsibility of the competitor.