Recorded Responses of a Light Truck With Rapid Left Front Air-Out of Super Oversized Mud Tires

Abstract

A closed-loop test of a 1974 Ford F-150 4WD truck equipped with super oversized off-road mud tires was conducted to demonstrate that steering was possible after a left front rapid air-out event. A rim was built with six remotely deployable orifices that activated simultaneously and caused the air pressure to decrease below 2.5 psi in less than one second. The truck was configured in OEM condition except for the tires and rims. The tires were 42–14X16 mounted to 8X16 rims with zero offset. The tires that were originally sold with the vehicle were probably 8.75–16.5. Three tests at increasing speed of 35 mph, 45 mph, and 55 mph were conducted on a large, remote, and closed parking lot in a two-lane travel way marked with surface paint. The truck, while monitored with a standard suite of instruments and video, was brought to speed in a straight-line. At a predetermined point, and while maintaining a straight path, the throttle was dropped and the left front tire air-out was remotely triggered. The driver, aware of the test conditions and with the benefit of experience, was instructed to steer the truck to maintain its position within the simulated traffic lanes. The truck was equipped with a four-speed manual transmission which remained in fourth gear throughout the response phase of the test. The clutch was depressed and brakes applied only after steering control had corrected the vehicle’s leftward motion. The post air-out path of the truck evidenced by printing from the left front tire in each test was measured, photographed and plotted. The truck never left the simulated roadway travel lanes, which represented one direction of a typical four-lane California state highway. The test data was recorded at 200 samples per second and was post-processed with a 6 HZ, 12-pole, phaseless digital filter. Test results were plotted and presented. The test results are of interest because they are a demonstration of the concept that even under extreme conditions, if a test driver knows what is going to happen and knows what to do, a controlled vehicle motion is the likely outcome. In the tests, as the driver gained experience and the speed increased, lateral motion decreased. These findings are consistent with conclusions in a NHTSA tread separation study including, “when drivers had prior knowledge of the imminent tread separation, they were significantly less likely to sustain loss of vehicle control following the tread separation.” And, “findings from test track studies in which test drivers were aware of an imminent tread separation may underestimate the extent to which tread separation occurring in the real world leads to instability and loss of vehicle control.”