15.4. Chassis
15.4.1. The Chassis or unitary construction must remain to the manufacturer’ s original specification in construction and material within the wheel hub centres with the exception of the following:
a. Re-positioning of suspension pick-up points and engine mountings are permitted. b. Inner wheel arches only may be modified to allow the attachment of damper mountings. c.
It is only permitted to make holes for the passage of cables fuel water oil hydraulic instrument or fire extinguisher lines as per ASN Vehicle Regulations. All redundant holes must be covered with metal plates.
d. Reinforcing of the Chassis is allowed.
e. Bulkheads and / or inner wings may be modified to permit the clearance of the induction system. This shall be understood to include air induction ducting manifolding trumpets / ram pipes for engine carburation or fuel injection system only.
f. Localised alteration for the passage / clearance of the exhaust system. 15.5. Bodywork( including aerofoils)
15.5.1. Silhouette of the Vehicle as seen in side elevation must remain unaltered with the exception of engine bonnet / cover and boot lid / rear deck.
15.5.2. The doors engine bonnet / cover luggage compartment cover boot lid / rear deck or bodywork not forming part of the unitary construction may be changed for ones of different material. Wheel arch extensions are free.
15.5.3. Alternative materials may be used for external mudguards if attached by bolts and / or rivets. 15.5.4. Detachable hardtops are permitted providing the silhouette remains unaltered.
15.5.5. It is permitted to replace any glass window with plastic Ch. 7 App. 2 Arts. 22.7 – 22.8 apply. A hole approximately 15cm diameter may be cut in the window next to the Driver for signalling or ventilation.
15.5.6. Demisting apertures are permitted in the rear windscreen / windows. They must be in the form of holes or slots and be positioned close to the top or sides but not both.
15.5.7. Open car with hoods may have them removed. Vehicles may run open or closed. If running closed a rear window of safety glass or plastic of minimum thickness 4mm is mandatory. Tonneau covers are permitted providing they are of flexible material and were originally specified for the Vehicle.
15.5.8. Front spoilers / air dams / splitters are permitted below the level of the road wheel centres up to 15cm beyond the overall plan periphery of the existing bodywork excluding bumpers.
15.5.9. Rear spoilers are permitted within the overall plan periphery of the original Vehicle excluding bumpers. A rear spoiler is a raised surface of opaque material integral with the rear deck with no gaps or openings in the surface front or rear and not exceeding half the vertical height of the original rear window fitted into the vehicle measured at the centre of the original window. The Vehicle manufacturer’ s original equipment or a specified option for that Vehicle is also permitted.
15.5.10. It is permitted to remove the floor carpets underfelt and sound insulation throughout the Vehicle as well as the rear seat the passenger’ s front seat and the head lining.
15.5.11. It is permitted to carry out modifications to window winders instrument panels and all driving controls.
15.6. Engine / Motors
15.6.1. The engine block must be externally identifiable as that fitted to the original model or a manufacturer specified option. Modification to all components is permitted.
15.6.2. With the exception of any engine fitted to a Vehicle complying with Art. 15.1.1 – 15.1.2 the engine must be of a make and type produced in at least 1000 identical units and fitted to a Vehicle originally
Motorsport UK National Competition Rules 2026 Edition 1
Chapter 14 Appendix 4- Technical Regulations 542