Canada: Update to TSD 139 on Parasitic Tread Block Chunking (PTBC)

 

Canada has published an update public consultation on Technical Standard Document (TSD) 139, New Radial Ply Tires.

This amendment follows feedback received during the winter tire consultation, which concluded on 18 February 2025.

During the consultation, manufacturers raised concerns regarding the endurance test requirements for passenger car tires. The test requires mounting the tire on a test rim and inflating it to the specified pressure. One possible failure mode under this test is “tire chunking,” where a portion of the tread detaches from the tire.

Manufacturers explained that, in certain cases, this outcome does not reflect the actual structural performance of winter tires. Instead, it is caused by Parasitic Tread Block Chunking (PTBC), which occurs when a winter tire reaches temperatures during testing that are significantly higher than those experienced under normal real-world driving conditions. According to manufacturers, such test results have prevented the importation of higher-performing winter tires into the Canadian market.

Based on the evidence and justification provided in the earlier consultation, Transport Canada has determined that an amendment to TSD 139 is warranted to address this issue for winter tires. The amendment introduces a definition of PTBC as a non-failure mode, aligned with international standards. Conventional tire chunking will remain a valid failure mode.

A six-month transitional period will apply following publication of the amendment. During this period, manufacturers may comply with either the previous or the amended version of TSD 139. After six months, compliance with the amended version will become mandatory.

The consultation is available under the link: https://tc.canada.ca/en/corporate-services/consultations/update-tsd-139-parasitic-tread-block-chunking-ptbc

To find out more about vehicle regulations in Canada, please do not hesitate to contact the Institute for Global Automotive Regulatory Research.