6. Brakes
6.1. Vehicles must not have separate braking of individual driven wheels( fiddle brakes) but it is permitted to increase the braking power of the Vehicle.
7. Springs and Shock Absorbers
7.1. Spring and shock absorber mounting points must be retained unaltered. In Classes B-D the springs and shock absorbers themselves may be changed and anti-roll bars and anti-tramp bars added.
8. Wheel and Tyres 8.1. Duplicated driving wheels are not permitted unless specified in the Official Documents.
8.2. It is permitted to replace standard wheels provided they can be fitted without altering the hubs or anything attached to them.
8.3. Tyre sizes and aspect ratios are free providing they are compatible with Construction and Use Regulations for the Vehicle concerned.
8.4. Use of the following tyres is prohibited:
a. those having any of the following patterns inscriptions or manufacturers’ designations:‘ All Seasons’‘ Grip’‘ Snow’‘ Special Use’‘ Town & Country’‘ Mud & Snow’‘ M + S’‘ M. S.’‘ M & S’ or the Three Peaks Mountain Snowflake symbol;
b. those constructed primarily for off-road use; c. those having additional grooves intentionally cut into the tread pattern [ post manufacture ]. d. Goodyear All Weather Steel Radial Goodyear Vector Pirelli P7 Michelin XRN or Uniband Rally Steel.
8.5. Tyres with sidewall markings removed are prohibited in all Events unless they are correctly marked‘ Retread’ or‘ Remould’.
8.6. Spare wheels and tyres must only be carried in the same numbers and mounting position( s) as provided by the manufacturer.
8.7. On the driven wheels only use minimum tyre pressures as specified in the Official Documents.
9. Transmission 9.1. Be fitted with non-torque biasing differential in full and free operation between the driving wheels unless:
a. A differential was not fitted by the manufacturer. b. The Vehicle is restricted to running in a nominated Class or Formula. 9.2. Vehicles must be two-wheel drive only unless the Official Documents allow four-wheel drive.
9.3. Four-wheel drive Vehicles operating in two-wheel drive mode are not eligible unless Permitted by the Official Documents.
9.4. If the Class structure suggested in Arts. 1.1 – 1.6 above is used then only gear and axle ratios as stated in the Official manufacturer’ s datasheet for the model and year of manufacture can be used except for Vehicles in Class D( b)
9.5. * Where components are changed to alter gear ratios as provided for above they must be readily interchangeable and from the same car manufacturer.
Motorsport UK National Competition Rules 2026 Edition 1
Chapter 17 Appendix 4- Technical Regulations- Car Trials Formula 625