Vehicle Technology and Standards Compendium 2003/2004

12th, January 2009

     
count: 4096

S340D(T)/VD Development of a test procedure for the measurement of truck tyre wet grip (incorporating the measurement of truck tyre rolling resistance)

Proposed regulatory controls on various aspects of truck-tyre performance, such as noise generation and rolling resistance, may have adverse consequences on the wet grip performance of these tyres. It is clear that wet grip performance needs to be monitored and, to this end, a research project was initiated project for the development of a test procedure for the measurement of truck-tyre wet grip during straight-line braking. It is recognised that the procedure has to be relatively inexpensive in terms of capital equipment and operating costs, but at the same time, has to be robust enough to yield statistically valid data.

The project was to establish the feasibility of the proposed test method for measurement of truck-tyre wet grip by:

  • assessing the feasibility of and, if appropriate, develop the proposals for a trailer based test procedure for wet grip assessment of new truck tyres,
  • evaluating the proposed test and compare alternatives, identifying and proposing solutions for potential problems that may be encountered with the proposed test/test equipment when used in variable ambient conditions, and
  • undertake rolling resistance measurements on a selection of currently available new and retreaded tyres.

The feasibility study consisted of a literature review and consultation with bodies experienced in tyre friction testing. Existing tyre testing experience of the contractor's personnel was also included.

Items specifically reviewed included:

  • Constant speed testing as opposed to deceleration testing.
  • Type of vehicle or machine to be used for testing.
  • Relevance of measuring peak and slide braking forces rather than braking force using ABS braking or braking force versus wheel rotational slip.
  • Control and accuracy of a vehicle on-board track wetting system.
  • Method of establishing a tyre reference datum (such as retaining a "collective" of current production tyres, including the number of such tyres to be used, how to store them, how to keep them up to date).
  • Validity of using the ASTM Standard Reference (car) Test Tyre as a control of test surface(s), including method of using.
  • Determining number and type of test surfaces to be used, and the number of test speeds to be used on each surface.

The methods of testing truck tyre wet grip properties have been examined by gaining information from an extensive literature survey and by seeking relevant expert opinion from research organisations and tyre and brake manufacturers.

There exists a causal link between tyre noise, rolling resistance and wet grip performance in that design changes that improve noise and/or rolling resistance may have a detrimental effect on wet grip. Future European legislation will be introduced to establish standards for tyre noise and rolling resistance and it is therefore considered important to monitor wet grip performance of existing and future tyre designs to ensure standards of wet grip performance do not suffer.

The establishment of a database of rolling resistance values for truck tyres together with research into wet grip performance will give an informed position from which to discuss the formulation of future European truck tyre legislation.

The main conclusions from this work are:

  • The feasibility of the proposed trailer-based test method has been accepted as workable. It is suggested that a drawbar trailer be used instead of a semi-trailer and that a single rear tyre is braked on the trailer.
  • A suitable braking strategy would
     

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