There is a lot of confusion regarding the correct manner in which to measure tyre tread depth. Even so-called tyre experts, such as the fitment centres disagree on the correct manner. Insurance companies often incorrectly reject claims on the basis that tyres did not comply with the roadworthiness requirements, while they in fact do. The correct manner is however described by law (South Africa), and although some sections are somewhat ambiguous when read in isolation, when one takes into account all the normative references in the National Road Traffic act and the applicable standards, such as the SABS 1550 and SABS 047, one is able to understand the correct procedure, as it applies to passenger vehicles/tyres. The information below was compiled for a trial and was accepted by the court.
The following documentation relates to the legal requirements concerning the tread depth of a tyre.
National Road Traffic Act and Regulations and other references:
Regulation 212 of the National Road Traffic Act, Act 93 of 1996 states the following:
212. No person shall operate on a public road–
j. a motor vehicle–
which is fitted with a pneumatic tyre unless such tyre displays throughout, across its breadth and around its entire circumference, a pattern which is clearly visible, and has a tread of at least one millimetre in depth; or
which is fitted with a pneumatic tyre which contains a tyre tread depth indicator, if the tread is level with the tyre tread depth indicator:
[Regulation 212 (j) (i) is applicable, where the tread depth is specified as at least 1mm. Subsection (j)(ii) relates to industrial tyres with no tread pattern. The tread depth indicator, differs from the “tread wear indicator” (TWI). The tread wear indicator is used on passenger tyres and is present inside the main grooves (where the tread depth is measured), to indicate that approximately 1.6mm of tread is still present, when worn to the level of the TWI.]
Regulation 129 states:
129. The requirements for registration of a testing station, are–
- the level of technical competence required in code of practice SABS 0216 “Vehicle test station evaluation”; and
- the manner of examination and testing of a motor vehicle at the testing station as required in code of practice SABS 047 “The testing of motor vehicles for roadworthiness”.
The normative references included in SABS 047 includes, but is not limited to the following:
Which forms part of SABS 1550 – 1 to 7: “Motor vehicle tyres and rims – Dimensions and loads”, which further refers to ARP 007 in the following manner. “Information on the care, maintenance and use of motor vehicle tyres and rims is contained in ARP 007.”
This means that the following documents are all used for determining condition of tyres in terms of roadworthiness:
- The National Road Traffic Act, Act 93 of 1996
- The National Road Traffic Regulations, 1999
- SABS 0216: Vehicle test station evaluation
- SABS 047: The testing of motor vehicles for road worthiness
- The vehicle Examiners Handbook, which contains guidelines for the vehicle examiner concerning the requirements of SABS 047
- SABS 1550: Vehicle tyres and Rims: Dimensions and Loads
- ARP 007: The care, maintenance and use of motor vehicle tyres and rims
The tread of a tyre must therefore be measured in the main grooves of the tyres and in other areas where the tread wear indicators indicate that the tread depth should be measured, as prescribed in ARP 007: 1992, “The care, maintenance and use of motor vehicle tyres and rims” reaffirmed on 2002-07-30.
Paragraph 188.8.131.52 states: “It is recommended that no vehicle be operated with tyres that do not have a minimum tread pattern depth of 1,0 mm in all the main grooves across the full width of their tread contact area and around the full tyre circumference, with the exclusion of areas where tread-wear indicators or tiebars (or both) exist.”
[IMPORTANT: If there are no main grooves, as in the case of some directional tyres, tread depth can be measured anywhere on the main tread surface, with the exclusion of areas where tread-wear indicators or tiebars (or both) exist.]
Paragraph 5.5.D. of the vehicle examiners’ handbook of the SABS, which is the guideline for vehicle examiners, corresponds with paragraph 5.5 of SABS 047, “The testing of motor vehicles for roadworthiness”. In these paragraphs, it is clearly indicated that the South African requirement for tread depth is 1mm, while the tread-wear indicators on the tyre are 1.6mm. The 1.6mm is a general international standard.
This basically means that the tyre must have a tread depth of more than 1mm over the breadth of the tyre and around the tyre’s circumference. The breadth may exclude the shoulder area on some tyres, depending on the design of the tread. This is because, it is common practice to have reduced depth of the grooves in the shoulder area of the tyre, to increase the stiffness of the shoulder of the tyre. This increased stiffness reduces tread squirm and associated wear. It therefore serves a specific purpose.
[Even though the national standard is only 1mm, and the general international standard is 1.6mm, it is the writers personal view that these values are insufficient and a minimum tread depth of 2mm is recommended.]
Additional to the above however, there is a requirement that a tyre should not be worn to a level where any part of the tyre construction is compromised. This is because a tyre can be worn or may suffer damage in an area to expose parts of the tyre construction. In such a condition, the tyre is weakened in more ways than one:
- The tyre has reduced penetration resistance
- The tyre has reduced impact resistance
- The tyre is less stable due to the weakening of sections of the construction
- Cords are exposed to the elements and may corrode or rot
SABS 047, section 5.5 paragraph f) therefore also states:
f) a tyre has any portion of the ply or cord structure exposed;”
This means that even if the tyre tread depth (in the main grooves), were measured and they comply with the specific requirements relating to tread depth, the tyre must be rejected.