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May/June 2011
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Radial Light Truck Tires

A need for a scientifically based procedure to identify equivalent test severity conditions between a 1.707-m diameter laboratory roadwheel surface and a flat or highway surface for radial pneumatic light truck tires has led to the development of a new ASTM International standard.

F2869, Practice for Radial Light Truck Tires to Establish Equivalent Test Severity Between a 1.707-m (67.23-in.) Diameter Rotating Roadwheel and a Flat Surface, was developed by Subcommittee F09.30 on Laboratory (Non-Vehicular) Testing, part of ASTM International Committee F09 on Tires.

“Testing for endurance, like many other tire tests, is usually performed in the laboratory on a 1.707-m diameter rotating roadwheel,” says Tim Robinson, manager, technical standards and regulations, Bridgestone Americas Tire Operations, and an F09 member. “The tire is rotated under load and speed on a surface that has a relatively high curvature compared to the highway, where the surface is nearly flat.”

According to Robinson, this difference between a flat surface and the roadwheel creates several tire effects that must be considered:

  • A foreshortening of the tire contact patch (or “footprint”) resulting in higher overall footprint contact pressures and tire stresses;
  • A change in shape of the footprint itself, i.e., different from its optimal, flat surface shape that increases the centerline contact pressure and tire stresses;
  • An overdeflection of the tire sidewall due to the reverse curvature of the footprint; and
  • An increase in the flex cycle severity.

A result of these effects is that local heat generation rates increase and tire temperature will often be significantly higher when the tire is tested on the roadwheel compared to a tire used on the road at the same load, inflation pressure and rotational speed. Consequently, laboratory test conditions that are equal to road conditions can result in end-of-test events that are not representative of typical highway tire removal conditions.

F2869 also uses special interactive electronic software called a prediction profiler, which can be used to determine laboratory test conditions that provide equivalent tire internal temperatures for the belt edge region for both the curved laboratory roadwheel and flat highway test surfaces.

CONTACT

Technical Information: Tim Robinson, Bridgestone Americas Tire Operations, Akron, Ohio

Phone: 330-379-4056

ASTM Staff: Rick Lake

Phone: 610-832-9689