UN R54 — Supplement 28 to the 00 series of amendments

The nominal rim diameter now means a conventional number denoting the diameter of the rim on which a tyre is designed to be mounted. The diameter is expressed either by codes (numbers below 100) or in millimetres (numbers above 100) but not both. Before, paragraph 2.20.4. described the “d” symbol, and numbers for both types of measurement could be used together in the designation. Paragraph 2.20.4. now only says “the nominal rim diameter”, and paragraph 2.20.4.1. is renumbered as 2.21.1. Paragraph 2.21.1. now starts with “When the nominal rim diameter ("d" symbol) is expressed by code”. Before, it read “The values of the "d" symbols expressed in millimetres are shown below:”.

New paragraph 2.14.1. defines “principal grooves” as the wide tread grooves positioned in the central zone of the tyre tread. The central zone is the area on the tread that comprises 75 per cent of the tread width, measured symmetrically from the centre line. New paragraph 2.37. defines “tread depth” as the depth of the principal grooves.

New paragraph 2.38. defines a “Free Rolling Tyre”. It is a tyre designed for the equipment of trailer axles and axles of motor vehicles other than front axles and drive axles. A “front axle” (new para. 2.38.1.) is any axle, forward of the mid-point of the chassis, on which the wheels are controlled by the steering system. Paragraph 3.1.15. now reads: the inscription “FRT” in case of a Free Rolling Tyre. Before, paragraph 3.1.15. itself described these tyres, with the words “other than front steering and drive axles”.

Paragraph 6.1.1.1. now says that the section width S of a tyre fitted on the measuring rim “shall be calculated by the following formula”. Before, it said that the section width “shall be obtained by means of the following formula”. A new line reads “and rounded to the nearest millimetre,”. The formula now shows a multiplication dot: S = S1 + K ∙ (A - A1). In the definition of S1, “the nominal section width” no longer has quotation marks. Paragraph 6.1.4. now reads “Tyre overall width specifications” in place of “Tyre section width specifications”.

For tyres of the category of use “snow tyre”, paragraph 6.1.5.3.3. gives a formula for the value that the outer diameter must not exceed. In this formula, Dmax is now the maximum outer diameter established for normal use tyres. Before, the text did not say “for normal use tyres”.

Paragraph 6.3.2. now says that, to be classified as a 'professional off-road tyre', a special use tyre must fulfil an additional requirement. For class C2 tyres, the maximum speed category must be less than or equal to 160 km/h (speed category symbol Q). For class C3 tyres, it must be less than or equal to 110 km/h (speed category symbol K). Before, paragraph 6.3.2. also listed a tread depth and a void to fill ratio for C2 and C3 tyres. The requirements for special use tyres give the same tread depth and void to fill ratio values. New item 4.2.1. of the communication form in Annex 1 reads: “For special use tyres, whether professional off-road tyre: yes/no”.

Paragraph 1 (Scope) excludes tyre types identified by nominal speed category corresponding to speeds below 80 km/h; it now adds “(speed category symbol F)”. Before, it said “nominal speed category symbols”. In the definition of “Type of tyre” (para. 2.1.), item (d) now reads “Structure (diagonal (bias-ply), radial (radial-ply))”. Item (f) now reads “Load-capacity indices” in place of “Load-capacity indexes”. In paragraph 2.36., an “additional service description” now means “a service description” in place of “an additional service description”. The footnote that refers to the Consolidated Resolution on the Construction of Vehicles (R.E.3) no longer gives the document symbol ECE/TRANS/WP.29/78/Rev.6.