Tyres. Only tyres which conform to the following specification may be used. All tyres will be measured mounted on the rim inflated to a pressure of 14 lbs/sq.in, and must have a nominal aspect ratio of 100/100. Overall width (O) measured at wheel spindle height must not exceed 115mm. (Refer to diagram). Tread depth
(A) must not exceed 13mm. All tread blocks in the same circumference must be of the same depth. The space between the tread blocks (B) must not exceed 9.5mm across the tyre or 13mm in a circumferential direction (C). The space between the shoulder blocks (D) must not exceed 22mm. The space across the tread (E) must not extend completely across the tyre measured at right angles to the tyre wall unless broken by a block. All main tread blocks must in principle be parallel with or at right angles to the tyre axis.
(Tyre must have the same appearance if reversed and conform in principle with these diagrams).
The tyre surface must not be fitted with any subsequently mounted elements such as anti-skid devices, chains,etc. NB: Only tyres available from commercial sources and complying with these dimensions are permitted in competitions. Where the event uses the public highway, tyres must be manufactured to comply with European Tyre & Rim Technical Organisation and have the relevant markings. Tyres for Long distance Trials Only tyres normally available from commercial or retail sources for use on the public highway (specification as above under “Tyres”) are authorised. They shall appear on the tyre manufacturers range catalogue or tyre specification list available to the general public. They must be manufactured to comply with European Tyre and Rim Technical Organisation (ETRTO) requirements in respect of load and speed codes and have a minimum service description of 45M. The use of MX and Enduro-type tread patterns are not permitted. The space between adjacent tread blocks must in principle not exceed 15mm (distance between tread block corners at diagonal groove intersections may exceed this dimension).