4.5. Any handle forward of the centre line of the rear axle must be fixed in accordance with dimension E as detailed in App. 7 Chart 1.
4.6. Rear mudguards must be of adequate strength to protect Driver and Passenger from wheels and tyres.
4.7. Rear mudguards must cover the full length of the tyre in plan-view at the top of the wheel and must extend outwards to within 5cm of the outside edge of the tyre wall.
4.8. Front mudguards must cover the full width of the tyre over an arc of 90 ° and extend rearward to not more than 10 ° above the horizontal line through the front hub.
5. Engine
5.1. Vehicles must use a single four-stroke production car engine not exceeding 1650cc. If forced induction is used, the coefficient will be 1.4:1 and 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.
5.2. Modifications are free.
6. Suspension 6.1. Any form of suspension can be used. For minimum track front and rear details see App. 7 Chart 1.
7. Steering 7.1. Any form of connection from steering wheel to the front wheels is permitted. 7.2. The position of the two swivel axes must not vary whilst steering. 7.3. Four-wheel steering is not permitted.
8. Brakes 8.1. Vehicles must be fitted with operative and effective front and rear brakes.
8.2. Independent rear braking is permitted but no self- compensating controls are permitted on the rear brakes which must be single leading-shoe drum brakes or disc brakes.
9. Wheels and Tyres 9.1. Duplicated driving wheels are not permitted.
9.2. Wheel rims must not exceed a width of 11.43cm( 4.5in) measured between the bead flanges nor a diameter of 15inches for driven wheels.
9.3. Tyre security devices are permitted in the rims. 9.4. Wheels should not carry any chains spikes or non-skid attachments.
9.5. Tyres must be of a maximum size 165mm x 15inches on driven wheels and must be selected from Ch. 8 App. 4 Tyre List 3.
9.6. Vehicles fitted with tyres that have previously been included in Ch. 8 App. 4 Tyre List 3 may compete for class awards only and may not be included in the overall classification.
9.7. Vehicles must carry one spare only which must be a driving wheel as fitted on the car fitted with any listed tyre. It is not permitted to add ballast to the spare wheel.
9.8. Motorcycle tyres on non-driven wheels are permitted. 9.9. Minimum tyre pressure 2psi.
10. Transmission 10.1. Vehicles must be equipped with a differential gear which divides torque equally between the driving wheels.
Motorsport UK National Competition Rules 2026 Edition 1
Chapter 17 Appendix 5- Technical Regulations – National Trials Car Formula
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