Abstract

In literature, it remains unclear how the friction coefficient of motor vehicle tyres and road surfaces is affected by velocity in vehicles fitted with antilock braking systems (ABS) compared to vehicles without ABS. In this paper, the effects of velocity on the friction coefficient of motor vehicle tyres and a paired road surface were examined. Tests were performed in a vehicle with ABS enabled and then disabled, allowing comparison between the two braking systems to be made. Braking, sufficient to cause skidding, was applied in a production large family sedan on a bitumen road surface. The friction coefficient of the vehicle tyres and bitumen road surface, during the skidding, was determined using a Vericombrake test computer fitted in the vehicle. Tests were conducted at a range of velocities between 32.8 km/h and 83.1 km/h, with the ABS being enabled and disabled. In both series of tests, peak maximum friction coefficient or minimum friction coeficient values were observed at around 40 km/h. With the ABS enabled, the lowest friction coefficient was observed at 41.9 km/h. When the ABS was disabled, the highest friction coefficient was observed at 42.2 km/h. As vehicle velocity was increased from 40 km/h, the friction coefficient of the vehicle tyres and road surface increased gradually when the ABS was enabled and decreased gradually when the ABS was disabled. Both series of tests showed evidence of plateau above 60 km/h. The vehicle with ABS enabled showed a decrease in the friction coefficient between 60 km/h and 80 km/h. The results suggest that a second peak may be observed around 70 km/h to 80 km/h or alternatively an ongoing plateau may occur. The friction coefficient of motor vehicle tyres and paired road surfaces is affected by velocity with both braking systems. The nature of the effect is dependent upon whether ABS is fitted and working.