Project: Development of a Test Procedure for Measurement of Tyre Wet Grip

Reference: S340D(T)/VD

Last update: 02/12/2003 09:53:55

Objectives

The project objectives are to:

* establish the current levels of tyre grip in wet conditions using a variety of car tyres from various manufacturers. (These tyres will then be assessed on the test tracks of five type approval agencies in order to obtain an average level of wet grip); and
* propose a test procedure for tyre wet grip that can be applied effectively by type approval authorities.

Description

Environmental pressure has led the European Commission to develop an amendment to the Tyre Directive (92/23/EEC) to include regulatory controls over the tyre to road noise emissions. There are fears, however, that this change will cause an imbalance in the traditional design compromise and lead to a reduction in tyre grip. This aspect of tyre design is not subject to regulatory control and a new test procedure is needed to ensure that at least the current levels of tyre grip are maintained in the future.

Contractor(s)

MIRA Ltd
Watling Street, Nuneaton, Warwickshire, CV10 0TU
+44 (0)2476 355000

Contract details

Cost to the Department: £119,684.00

Actual start date: 01 September 2002

Actual completion date: 31 March 2004

Publication(s)

02-215112. Measurement of Truck Tyre Rolling Resistance
Author: MIRA Ltd
Publication date: 13/06/2003
Unpublished
Source: Contact lawrence.thatcher@dft.gsi.gov.uk

03-0215111. Development of a Test Procedure for the Measurement of Truck Tyre Straight Line Wet Grip
Author: MIRA Ltd
Publication date: 01/03/2004
Unpublished
Source: Contact: lawrence.thatcher@dft.gsi.gov.uk

Summary of results

  1. The main conclusions from this work are that:

    * 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 be to ramp the brake pressure over a period of about 1 second, releasing the brakes just after lock up to avoid tyre damage. Sliding friction would be computed by means of a curve fitting procedure;
    *the number of tyres that may be tested in one day is probably no more than seven. This means that, if more than one candidate tyre is to be tested, the test schedule would have to be conducted over two or more days;
    * test conditions would need to be very tightly controlled, if meaningful data are to be collected, especially if testing were to take place over several days. A method for correlating data collected over several days is suggested;
    * a considerable volume of water would be needed for a complete days testing (up to 5000 litres). It is concluded that this decreasing weight of water would best be carried on a truck with a drawbar trailer, rather than on a semi-trailer, where the vertical load on the test wheel would be affected;
    * track texture would have to be specified in order that tests are only carried out on representative surfaces;
    * within a group of new tyres it is possible to see significant variations in rolling resistance, but it is not possible to say that the products of particular manufacturers perform any better than others;
    * retreads almost exclusively have greater rolling resistance than the equivalent new tyre;
    * on average, the 295/80 R 22.5 steer axle tyres have a lower rolling resistance than drive axle tyres of the same size;
    * the 'wide single' trailer tyres have a lower rolling resistance than conventional trailer tyres; and
    * not all tyres branded as low rolling resistance showed significantly lower values than those with no claim to energy efficiency.