Setting the Tester. Set the Tester on the road surface in the track to be tested so that the Rubber Slider swings in the direction of the traffic. Condition the slider by swinging it five times across the dry road surface. On surfaces bearing a regular pattern such as ridged or brushed concrete, tests should be made with the conditioned Rubber Slider operating at 80° to the ridges. Take the mean of five readings, as above, at each of five locations in the test track (usually the near side wheel-track) spaced at approximately 5 to 10 metre intervals along the length under test. The mean of these readings gives a representative value of the skidding resistance of the road.

The slipperiness of some roads varies considerably across the width of the road and sometimes the crown of the road is the most slippery part. Where this is suspected, tests should also be made on the crown of the road.

Gradients. The Tester is capable of performing tests on steep gradients and in the presence of crossfall. On gradients, the above procedure is followed and, although the sliding length is slightly displaced from the central position, there is no change in the load between Rubber Slider and test surface and no appreciable change in the speed of sliding. Therefore, the instrument operates correctly whether tests are performed uphill or downhill. Sufficient levelling adjustment is available for testing on gradients of up to I in 10 (5.7°). Inserting a spacer under one screw allows the Tester to be used on steeper gradients.

Factors affecting results. Like all skidding machines, the Portable Skid Resistance Tester can  only be used to the best advantage with a full knowledge of the  factors influencing skidding resistance, and results must be interpreted  with due consideration for all conditions obtained at the time of the  tests. The main factors influencing skid resistance are outlined below:

The measurement obtained by the Portable Skid Resistance Tester has been termed 'Skid Resistance'. It is intended to correlate with the performance of a vehicle having patterned tyres, braking with locked wheels, on a wet road at 50 Km/hr.

The order of merit of road surfaces can change substantially between 50 and 130 Km/hr. Thus, Skid Resistance values, which represent the 50 Km/hr value, cannot alone be expected to give an indication of high-speed performance.

The fall-off in Skidding Resistance with increased speed on wet roads depends on the roughness of surface macro-texture, and is considerably less on rough surfaces than on smooth ones.

If the tester is used on high-speed roads, an additional criterion indicating texture is required. Because the Portable Skid Resistance Tester indicates the performance of patterned tyres at relatively low speeds, it is important to record the surface texture or appearance of each road surface tested. On roads where speeds are low it is sufficient to classify the texture from visual inspection.

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Portable Skid Resistance Tester Manual