retained.
4. Engine
4.1. The engine must comply with Ch. 7 App. 2 Art. 8 regarding positive throttle closure by external springs unless exempt due to the use of original standard manufacturer fitted electronic throttle control.
4.2. If forced induction is used, the coefficient will be 1.4:1.
4.3. There are no restrictions on engine tuning providing the cylinder block is of the same manufacture and configuration as the original.
4.4. The make type and number of carburettors is unrestricted.
4.5. The position of the engine mountings in the chassis may not be altered. Any further modifications will cause the Vehicle to be reclassified to Class 7( a).
4.6. No part of the external exhaust system may be more than one metre above the ground.
5. Brakes 5.1. Vehicles must not have separate braking for individual driven wheels( fiddle brakes).
6. Suspension 6.1. Springs and shock absorbers may be changed and additional springs and shock absorbers fitted. 6.2. Anti-tramp and anti-roll bars Panhard Rods and Watts Linkages are permitted.
6.3. Except for Classes 7( a) and 8 the original springing system and spring mounting points must be retained in operational use eg leaf spring systems must retain at least the minimum number of leaves specified by the manufacturer and must not be replaced by coil or other springing systems.
7. Wheels and Tyres 7.1. Duplicated driving wheels are not Permitted unless specified in the Official Documents. 7.2. Competitors must carry a spare wheel and tyre as a replacement for one wheel on the Vehicle.
7.3. Wheels of up to the standard diameter must be used except for Classes 5( c) 7( a) and 8 where wheel diameter is free.
7.4. In Class 8 the maximum tyre section must be 185mm.
7.5. In all Classes 1 to 8 and 90( except Class 2) the maximum permitted difference between front and rear tyres must be two sections.
7.6. No tyre may be smaller than that recommended by the car manufacturer.
7.7. Standard tyres must be used and all types of Grip and Town & Country block patterns are prohibited. Radial tyres with a maximum tread gap exceeding 8mm are prohibited. A tyre will be deemed to have a block gap not exceeding 8mm if when fitted to a rim and inflated to 25psi an 8mm round bar will stick in the gap when horizontal. Purely circumferential gaps may be ignored.
7.8. In all Classes spare wheels must be firmly secured by a permanent fixing.
7.9. Not more than two spare wheels may be carried externally and these must be fitted as close as possible to the bodywork( excluding bumpers).
7.10. No part of the spare wheel( s) may be mounted externally in front of the windscreen unless in the manufacturer’ s standard position or on the roof.
7.11. Vehicles with an external rear-mounted spare wheel in the manufacturer’ s standard position may add a second spare wheel mounted flush with the original wheel with no spacer.
Motorsport UK National Competition Rules 2026 Edition 1
Chapter 17 Appendix 3- Technical Regulations- Classic Reliability Trial Vehicles
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