Effects of velocity, temperature and rainfall on the friction coefficient of pneumatic tyres and bitumen roads

A world without friction would be a world of destruction. Friction is a consequence of the laws of physics. The laws of motion and friction predict that kinetic friction will not be affected by velocity, ambient temperature and rainfall. This hypothesis developed hundreds of years ago is based primarily on research of objects and surfaces with metallic properties. Pneumatic tyres on motor vehicles have viscoelastic properties. Researchers have identified that polymers such as pneumatic tyres do not to follow the laws of friction. Research into the friction coefficient of pneumatic tyres and road surfaces is new and remains elusive as both road surfaces and vehicle design continues to develop. Vehicle safety and collision investigation relies greatly on accurate determination of tyre and road surface friction. This study is designed to determine the effect of vehicle velocity, ambient temperature and rainfall on the friction coefficient of pneumatic tyres sliding on bitumen road surfaces. Where an effect is identified, formula will be developed to facilitate the prediction of friction where vehicle velocity, ambient temperature and rainfall may be relevant factors. To determine the effect of velocity, temperature and rainfall on the friction coefficient of pneumatic tyres and road surfaces, three series of tests were undertaken. Skid resistance tests were performed in a passenger vehicle on bitumen roads at a range of speeds between 30 km/h and 80 km/h, with and without antilock braking, at a range of temperatures between 3°C and 43°C and pre, during and post rainfall. The friction coefficient for each variable was determined using an accelerometer. Results identified that when a vehicle skids with antilock braking, the friction coefficient of the tyres sliding on the road surface will increase as velocity increases. When a vehicle skids without antilock braking, the friction coefficient will decrease with increasing velocity. As temperature increases, the friction coefficient increases linearly. The friction coefficient of tyres sliding on roads at 60 km/h will increase in periods of heavy rain and decrease on a wet road after a period of rainfall, comparative to dry road friction. A solution was developed to facilitate friction coefficient prediction. Where any analysis of the friction coefficient of pneumatic tyres sliding on road surfaces is necessary, the developed models can be used to account for any variation due to velocity and temperature. It is possible to predict friction using this model. A similar model was developed to account for changing vehicle velocity. Prediction models were not developed for rainfall. The testing procedure did not facilitate the ability to quantify the effect of rainfall. A need for innovative ideas would be necessary to quantify the effect of rainfall on friction of pneumatic tyres and road surfaces. This research will provide valuable information for road design engineers and collision investigators worldwide regarding the effects of vehicle velocity, ambient temperature and rainfall on the friction coefficient of motor vehicle tyres and road surfaces. The findings have the potential to increase road safety and advance collision reconstruction and investigation.<br><br>