Sliding Decelerations of Motorcycles on Wet Surfaces - An Brief Technical Note

In a prior post, examined how certain motorcycle characteristics affect the deceleration when the motorcycle is sliding on the road: fairings, crash bars, frame sliders, and the like. That post did not address the influence of a wet road. In this post, I offer a brief technical note to document two studies that have shown that a wet roadway reduces a sliding motorcycle’s deceleration, compared to what it would have been on a dry roadway. This is an area that could use more testing and research.

Hague [1] compiled tests of motorcycles sliding on wet surfaces from studies published in German. He concluded that the decelerations were marginally lower than on dry surfaces. No data was provided related to the procedures or motorcycles utilized in the underlying studies, and Hague did not quantify what he meant by “marginally lower.” A study by Chih-Yung Lin [2] examined decelerations of 125cc scooters (“light motorcycles”) sliding on both dry and wet asphalt roads. This study utilized a procedure in which the scooters were upright while being towed up to speeds between 25 and 50 km/h (15 to 31 mph), then they were allowed to fall to ground and slide to rest. Eighteen tests were conducted on a dry road, and these resulted in decelerations between 0.36g and 0.53g. The average deceleration from these tests was 0.428g and the standard deviation was 0.046g. Seven tests were conducted on a wet roadway, and these resulted in decelerations between 0.29g to 0.40g. The average deceleration from these tests was 0.340g and the standard deviation was 0.037g. Thus, the tests on a wet road exhibited decelerations that were approximately 0.09g lower than those on a dry road.  

[1] Hague, D., “Calculation of Speed from Motorcycle Slide Marks,” Impact: The Journal of the Institute of Traffic Accident Investigators, Spring 2004.

[2] Lin, Chih-Yung, et al., “The study of coefficient of friction for light motorcycle sliding on asphalt road,” International -Journal of the Physical Sciences, Vol. 7(30), pp. 5167-5174, 9 August 2012.