Measurement of Changes to Vehicle Handling Due to Tread-Separation-Induced Axle Tramp

Tests were conducted to evaluate the effects of the tire-induced vibration caused by a tread separating rear tire on the handling characteristics of a 1996 four-door two-wheel drive Ford Explorer. The first test series consisted of a laboratory test utilizing a 36-inch diameter single roller dynamometer driven by the rear wheels of the Explorer. The right rear tire was modified to generate the vibration disturbance that results from a separating tire. This was accomplished by vulcanizing sections of retread to the prepared surface of the tire. Either one or two tread sections covering 1/8, 1/4, or 1/2 of the circumference of the tire were evaluated. The results demonstrated that a tire modified with two bonded-on tread sections driven at half speed replicated axle tramp characteristics of a modified tire with a single bonded-on tread section at the peak axle tramp speed. A second test series consisted of low speed vehicle handling tests with a right rear tire modified with two bonded-on tread sections. The on-road testing showed that the modified right rear tire caused axle tramp and associated vehicle skate at the peak axle tramp speed during quasi-steady state and dynamic maneuvers. A 1999 four-wheel drive Ford F-250 truck was tested with a tire modified by cutting away 1/4 of the tread and outer belt at two locations. The modified tire was placed at the left front position and low speed vehicle handling tests were conducted at the peak axle tramp speed. Test results show front-axle tramp induced an increase in steer gradient and significantly reduced turning capability.