A Dynamical Analysis of a Towed Two-Wheel Trailer1

The towed trailer method for skid resistance measurements is a practical one for characterizing the friction characteristics of highway pavements, and has been standardized by the ASTM 11). Numerous papers have been published about the improvement of equipment and field-testing techniques but little has been done toward a theoretical explanation.

This paper presents a mathematical model of the trailer which includes roll, pitch, and vertical motion. The skid resistance calculated by using this model gives an excellent check on the standard ASTM skid number formula. The response time and damping effect after locking one test wheel can be clearly seen in this model. Possible effects of the dimensions of trailer, stiffness of suspension system, tire pressure, etc. to skid resistance can also be examined.