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UN R108 Supplement 1 (01 series) · UNECE Regulation No. 108 (ECE R108) — Uniform provisions concerning the approval for the production of retreaded pneumatic tyres for motor vehicles and their trailers.

UN R108 — Supplement 1 to the 01 series of amendments

Base text → Supplement 1

Adopted at the WP.29 196th sessionEntry into force 2026-01-11
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What changed
  • Principal grooves (paragraph 2.14.1.) are now the wide tread grooves positioned in the central zone of the tyre tread, and new paragraph 2.15. defines “Tread depth”.
  • Under paragraph 2.22., the nominal rim diameter is expressed either by codes (numbers below 100) or in millimetres (numbers above 100) but not both.
  • References to “UN Regulation No. [XXX]” now read “UN Regulation No. 172”.
Why
  • It was proposed to amend the definition of principal grooves by eliminating the circular reference between this definition and the position of tread wear indicators.
  • The provisional number [XXX] of the adopted UN Regulation on retreaded tyres (snow performance and/or classification as traction tyre) is replaced with 172.
  • The end of the introductory sentence in paragraph 3 of Annex 3 was missing, because dots in a GRRF document were not taken into account.

Q1What changed37 changes

Tread groove, principal grooves, secondary grooves and tread depth (paras. 2.14., 2.14.1., 2.14.2. and 2.15.)

Paragraph 2.14. now uses the term “Tread groove” in place of “Tread pattern groove”, and says “ribs and/or blocks” in place of “ribs or blocks”. Former paragraph 2.15. on “Principal grooves” is now paragraph 2.14.1. Principal grooves are now the wide tread grooves positioned in the central zone of the tyre tread. Before, they were the wide circumferential grooves in the central zone, which have the tread-wear indicators located in the base. The central zone is the area on the tread which comprises 75 per cent of the tread width, measured symmetrically from the centre line. New paragraph 2.14.2. defines “Secondary grooves”, and new paragraph 2.15. defines “Tread depth” as the depth of the principal grooves.

"Tread pattern groove" means the space between two adjacent ribs or and/or blocks in the tread pattern.;
"Principal grooves" means the wide circumferential tread grooves positioned in the central zone of the tyre tread, . The central zone is the area on the tread which have comprises of 75 per cent of the tread-wear indicators located in width of the basetread measured symmetrically from the centre line. The central zone is the area on the tread which comprises of 75 per cent of the width of the tread measured symmetrically from the centre line.
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Nominal rim diameter (paras. 2.21.4., 2.22. and 2.22.1.)

Paragraph 2.22. now defines “Nominal rim diameter” as 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 2.21.4. gave this conventional number and said that numbers for both types of measurements may be used in the designation. Paragraph 2.21.4. now reads “The nominal rim diameter”. Former paragraph 2.21.4.1. is now paragraph 2.22.1., and it gives the values of the “d” symbol when the nominal rim diameter is expressed by code.

"Nominal rim diameter (d)" " 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.
A conventional number "d (the "d" symbol) denoting the nominal rim diameter of the rim and corresponding to its diameter expressed either by codes (numbers below 100) or in millimetres (numbers above 100). Numbers corresponding to both types of measurements may be used in the designation.The nominal rim diameter
1 more change in this group — open in Compare

Renumbered structure indications in the tyre size designation (paras. 2.21.3.2., 2.21.3.3. and 2.21.3.3.1.)

Former paragraph 2.21.3.3. on bias-belted tyres is now paragraph 2.21.3.2. Former paragraph 2.21.3.2. on radial-ply tyres is now paragraph 2.21.3.3. Former paragraph 2.21.3.4. on radial-ply tyres suitable for speeds in excess of 240 km/h but not exceeding 300 km/h is now paragraph 2.21.3.3.1.

2.21.3.3.2.21.3.2.
2.21.3.2.2.21.3.3.
1 more change in this group — open in Compare

Snow tyre definition and list of tyres for use in severe snow conditions (paras. 2.3.2. and 4.1.5.3.2.)

In the definition of “Snow tyre” in paragraph 2.3.2., the words “major features including tread pattern” replace “tread pattern, tread compound or construction”. In paragraph 4.1.5.3.2., the words “and/or as traction tyres” are deleted from the list of tyres classified as tyres for use in severe snow conditions.

"Snow tyre" means a tyre whose major features including tread pattern, tread compound or construction is are primarily designed to achieve, in mud and/or snow conditions a performance better than that of a normal tyre with regard to its ability to initiate and control vehicle motion.
The list of tyres classified as tyres for use in severe snow conditions and/or as traction tyres.

Calculation of the section width and overall width heading (paras. 7.1.1.1. and 7.1.4.)

Paragraph 7.1.1.1. now refers to the section width S “of a tyre fitted on the measuring rim”. The formula now reads “S = S1 + K · (A − A1)”, and the result is rounded to the nearest millimetre. The entry that defined S as the actual section width measured on the test rim is deleted. Paragraph 7.1.4. now has the heading “Tyre overall width specifications” in place of “Section width specifications”.

The section width S of a tyre fitted on the measuring rim shall be calculated by the following formula:
S = S1 + K · (A - − A1)),
3 more changes in this group — open in Compare

UN Regulation No. 172 in place of “No. [XXX]” (paras. 2.48., 2.55., 3.4.1., 4.1.5.3.2.1. to 4.1.5.3.2.3. and 6.6.3.1. to 6.6.3.4.)

References to “UN Regulation No. [XXX]” now read “UN Regulation No. 172”. This change applies in paragraphs 2.48., 2.55., 3.4.1., 4.1.5.3.2.1. to 4.1.5.3.2.3. and 6.6.3.1. to 6.6.3.4.

"Supplier of the tread used for retreading process" means the person or body who is responsible to the Type Approval Authority for all aspects of the type-approval under UN Regulation No. [XXX].172.
"Tyre for use in severe snow conditions" means a snow tyre or a special use tyre whose major features including tread pattern are specifically designed to be used in severe snow conditions and that fulfils the requirements of paragraph 6.1. of UN Regulation No. [XXX].172.
16 more changes in this group — open in Compare

Wording of paragraph 1.1. and of Annex 3, paragraph 3.

Paragraph 1.1. now says “a speed category below 120 km/h or suitable for speed above 300 km/h”. Before, it said “a speed category symbol below 120 km/h or above 300 km/h”. In Annex 3, the introductory sentence of paragraph 3. now reads “The positioning and order of the markings shall be as follows”. Before, it ended after “The positioning and order of”.

Retreaded tyres with a speed category symbol below 120 km/h or suitable for speed above 300 km/h;
The positioning and order of the markings shall be as follows:
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Q2Why it changed

Proposed by
Experts from the European Tyre and Rim Technical Organization
Working party
GRBP, 81st session (February 2025)

Reasons

  • The snow tyre definition is now aligned to the definitions in UN Regulations Nos. 109 and 172. The definition of nominal rim diameter is clarified.

    Sources (2)
    “The snow tyre definition in now aligned to the ones in UN Regulations Nos. 109 and 172.”
    “The definition of nominal rim diameter is clarified.”

  • It was proposed to amend the definition of principal grooves by eliminating the circular reference between this definition and the position of tread wear indicators. The new definition of tread depth is used in the requirements for special use and professional off-road tyres.

    Sources (2)
    “An amendment is proposed for the definition of principal grooves by eliminating the circular reference between this definition and the position of tread wear indicators.”
    “The definition of tread depth is introduced, which is used in the requirements for special use and professional off-road tyres.”

  • It was proposed to remove the reference to traction tyre classification in paragraph 4.1.5.3.2., because it is not applicable to tyres of class C1. The calculation of the tyre section width is clarified.

    Sources (2)
    “An amendment is proposed in paragraph 4.1.5.3.2. to remove the retreaded reference to traction tyre classification because it is not applicable to tyre of class C1.”
    “The calculation of the tyre section width is clarified.”

  • The provisional number [XXX] referred to the adopted UN Regulation on the approval of retreaded tyres for snow performance and/or classification as traction tyre. At every occurrence in the text, it is replaced with the assigned number 172.

    Source
    “At every occurrence in the text, the provisional number [XXX] of the adopted UN Regulation concerning the approval of retreaded tyres with regard to their snow performance and/or classification as traction tyre is replaced with the assigned number 172.”

  • The end of the introductory sentence in paragraph 3 of Annex 3 was missing. The dots in document TRANS/WP.29/GRRF/2002/18/Rev.2 were not taken into account when it was converted into document TRANS/WP.29/2004/49. The original introductory sentence also mentioned only the marking of the tyre size designation. The proposed amendment is deemed to remove all these inconsistencies.

    Sources (4)
    “The end of the introductory sentence in paragraph 3 of Annex 3 is missing, because the dots (……) contained in document TRANS/WP.29/GRRF/2002/18/Rev.2 adopted by the Working Party on Brakes and Running Gear (GRRF), were not taken into account”
    “when it was converted into document TRANS/WP.29/2004/49 adopted by the World Forum for Harmonization of Vehicle Regulations (WP.29).”
    “the original introductory sentence did not properly reflect the subsequent points, because it mentioned only the marking of the tyre size designation without mentioning the other markings referred to in paragraph 3.”
    “The proposed amendment is deemed to remove all these inconsistencies.”

Document trail

  1. 2024-07ProposalECE/TRANS/WP.29/GRBP/2024/24Proposal by the experts from ETRTO for Annex 3, paragraph 3.
  2. —Working party adoptsECE/TRANS/WP.29/GRBP/78Session report, para. 24: correction adopted, submission postponed
  3. 2024-12ProposalECE/TRANS/WP.29/GRBP/2025/15Proposal by the experts from ETRTO for a new Supplement to the 01 series
  4. —RevisedGRBP-81-11-Rev.1Proposal to replace GRBP/2025/15, transmitted by the experts of ETRTO
  5. —Working party adoptsECE/TRANS/WP.29/GRBP/79Session report, para. 15
  6. 2025-04Sent to WP.29ECE/TRANS/WP.29/2025/73Text that GRBP sent to WP.29 and AC.1
  7. 2025-06WP.29 adoptsECE/TRANS/WP.29/1186Adopted at the 196th session (session report, para. 111)
  8. 2026-01-11In forceC.N.32.2026.TREATIES-XI.B.16.108UN depositary notification

Q3Who is affected

Vehicle manufacturer

  • No direct action for this role.

Component supplier

  • Measure tread depth in the principal grooves: the wide tread grooves positioned in the central zone of the tyre tread.

Technical service / Approval authority

  • For special use and professional off-road tyres, check tread depth as the depth of the principal grooves.

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ⓘ This report gives advice only. It is not legal or type-approval advice.

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