Experimental Skid Analysis of a Vehicle on a Gravel Road

Abstract

Skid control on a typical dry rural sandy, gravel road had been investigated, to identify the skid and braking characteristics. Experimental analysis was performed on a vehicle travelling at three different speeds (80, 60 and 40 km/h) and for each speed three different levels of tyre wear condition (tyres with tread as new, approximately 38% and wholly illegal or below tread wear indicator level). The effect of severe tyre pressure difference on one side of the vehicle combined with the illegal tyres was also considered. Testing was undertaken with and without ABS braking. A drag factor (based on drag sled values obtained on the test section) of 0.52 was used as a theoretical value and basis of determining skid / stop distance. The results of these tests are that • The skid distances were observed to be similar to the theoretical skid distances (based on drag sled determined drag factors) when no ABS brakes were used. • The general observation was that the skid distances on gravel increased, the smoother the tyres were. • The observed differences between the different inflation levels of the tyres, showed a small difference. • All runs where the RHS tyres were underinflated (1.1 bar or 50% inflation), presented with an obviously clearer, more defined ABS braking mark on the right side tyres, compared to the fully inflated tyres. • There was generally a difference when the ABS brakes were activated, as the skid distance was more than the theoretical skid distance (based on drag sled determined drag factors). • When the ABS brakes were deactivated, the vehicle skid out of control, yet when it was activated, the skid of the vehicle was in a straight line. • Correction factors that could be used to calculate a more accurate skid distance on gravel roads using drag sled determined drag factors; when ABS brakes were used was found to be 1.165; and for illegal tyres 1.3.