This research investigated the effect of road roughness, macrotexture and testing speed on GripTester measurements.
Field tests were conducted by the GripTester at various test speeds on sites with varying road roughness in South Auckland. The variables – road roughness, texture and test speeds – were measured and plotted against each other along with grip number (GN) as obtained from the GripTester. Tests with the DF Tester were also carried out at one site and directly correlated with GripTester results at various towing speeds. It was found the GN might not be dependent on test speeds while testing at speeds lower than 75km/h; however, an inverse relationship occurred at higher speeds, on a limited number of test sites. Road roughness was found to have no effect on GripTester measurements and texture appeared to be a minor factor.
In conclusion, the explanatory variables on the GN are test speed and perhaps texture. However, unaccounted factors that are specific to test sites proved to have some degree of effect. Future research recommendations include searching for better controlled test sites and larger samples to clarify the effect of texture on the GN and to expose unidentified factors that can influence GripTester output.