Proceq SRT 5800 Manual page 8

Because the portable 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. Plate
2 shows typical surfaces classified as follows:
Plate 2 (a) and (b): rough-textured surfaces where tyre
tread pattern would have a negligible effect; smooth and
patterned tyres would generally be equally effective on
these surfaces.
Plate 2 (c) and (d): medium-textured surfaces where some
tread pattern effect would exist; vehicles having smooth
tyres would experience a skidding resistance slightly lower
than the value indicated by the tester.
Plate 2 (e) and (f): smooth-textured surfaces where the
effect of tread pattern may be large.
On roads where speeds are high, a simple measure of
surface texture, the 'texture depth', may be determined by
the 'sand patch' method: a known volume of fine sand is
poured in a heap on the road, and spread to form a circular
patch so that the small valleys on the road are filled to the
level of the peaks; the 'texture depth' is the ratio of the
volume of sand to the area of the patch (calculated from the
measured radius). The additional details of the test are
given in the Appendices, which also describe a simple
method of taking close-up surface photographs with
standard conditions of illumination. This provides a useful
record of the appearance of the surface.
2. In general the skidding resistance of wet roads is
higher in winter than in summer. The magnitude of the
variation depends on (a) road layout and traffic
conditions, (b) road surface characteristics, and (c)
the weather; it varies considerably from one road to
another, so that it is not possible to predict the
skidding resistance at one time of year from a single
measurement made at another time. It is also
important to note that roads with satisfactory values in
winter (especially in December, January, and
February) may prove slippery during the summer. The
date of test should therefore always be recorded.
3. The effect of temperature on rubber resilience exerts
a perceptible influence in all skidding resistance
measurements; 5 it shows itself as a fall in skidding
resistance as the temperature rises. In addition, the
magnitude of the variation of skidding resistance with
temperature varies considerably from road to road,