Wide single tires get national acceptance; in principle

OTTAWA — The provincial Ministers of Transportation recently agreed the new generation of wide base single tires are deserving of increased weight limits.

In April 2008 the Council of Ministers Responsible for Transportation and Highway Safety approved several amendments to the MOU on Vehicle Weights and Dimension, which will be implemented July 1.

The council notes research has proven the new wide base single tire designs offer improvements in fuel efficiency, vehicle roll stability and reduced tare weight. While the new designs also offer reduced impacts on pavement compared to the older wide single tires, they still appear to have slightly higher impacts than the dual tire configuration they replace if used at dual tire loads.

To improve the consistency of weight limits applicable to use of these tires across Canada, while also protecting highway infrastructure, the national standards for weight limits on single and tandem axle groups are being increased to the federal limits currently applicable in the U.S.

Under the new clause in the MOU, when an axle – except for steering axles – is fitted with two single tires, each of which has a width of 445 mm or greater, do not exceed 7,700 kg for single axles and 15,400 kg for tandem axle groups.

And of course, there are some exceptions. The Northwest Territories will retain a weight limit of 3,000 kg for any single tire except on steering axles; in New Brunswick the weight on a single tire (except on steering axles) having a minimum width of 445 mm can not exceed 3,080 kg on highways rated as Class 3 – GVW up to 50,000 kg and Class 4 – GVW up to 43,500 kg, and the weight on a single tire (except on steering axles) having a width of less than 445 mm can not exceed 3,000 kg on all New Brunswick highways; and in Newfoundland and Labrador the weight on a single tire (except on steering axles) can not exceed 3,000 kg on secondary roads within the designated route network.

Along with the introduction of wide single tires will be a length allowance for rear mounted aerodynamic devices.

Research has shown that devices attached to the rear of trucks and trailers can improve aerodynamic efficiency and improve fuel economy by up to 5 percent. Since the devices do not cause detrimental impacts during turning, the Council has determined such devices shall not be included in the measurement of overall length, trailer length, semi-trailer length, box length and effective rear overhang.

It is important to note however, under the terms of the MOU, provinces and territories are not obliged to adopt the specific weight and dimension limits contained in the MOU, but will ensure that their regulations are not more restrictive than the national standards for vehicles traveling on their designated highway systems.

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