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The concept of vehicle understeer and oversteer has been well studied and equations, test methods, and test results have been published for many decades. This concept has a specific definition in the steady-state driving range as opposed to quantification in highly transient limit handling events. There have been specific test procedures developed and employed by automotive engineers for decades on how to quantify understeer. These include the constant radius method, the constant steering wheel angle/variable speed method, the constant speed/ variable radius method, and the constant speed/variable steer method. These methods are very good for calculating the understeer gradient but care must be taken in interpreting the result at the limits of tire traction since lateral tire forces can be reduced on a drive axle when significant throttle is applied.

In this study, tests were performed on eight different vehicles, each equipped with a version of electronic stability control (“ESC”). Tests performed on a dry test surface included a 1999 two door sports car, a 2000 four door sedan, a 2002 four door sedan, a 2003 large rear wheel drive sport utility vehicle, and a 2002 five door hatchback. Tests performed on a wet surface were isolated to a full size rear wheel drive sport utility vehicle. Tests performed on a snow and ice covered surface included a 2003 mid size sport utility vehicle, a 2002 full size sport utility truck, and a 2007 mid size sport utility vehicle; all from different manufacturers. This selection allowed for the evaluation of different ESC systems and strategies on various surfaces to violent steering demands. The steer inputs were applied to the vehicles manually by test drivers and were purposely selected to generate large displacements so that the ESC systems would activate.

In repeated physical testing of vehicles at or near their handling limit, tire shoulder wear occurs that is not typical of normal customer use. It has been observed for decades that this type of severe cornering induced tire wear can have a significant effect on the force and moment characteristics of tires. In this study, the severe cornering wear effect was studied by testing vehicles in a highly controlled manner using a robot steering controller. This testing shows how vehicle response to the exact same steering input changes significantly as the number of runs on the same tires accumulates. In fact, vehicles were found to not lift tires from the ground in initial runs then tip-up hard onto outriggers in later runs as the tires are abraded. Additionally, for one vehicle configuration an additional run was made with tires that had accumulated 16,000 km (10,000 miles) of normal customer usage.

In this study, tests were performed with modified tires on twenty-two different vehicles to measure their steering and handling capacities with a fully separated tire. Vehicles were tested with delaminated tires (i.e. tires where the tread and upper steel belt were removed) placed on the front suspension as well as the rear. These tests were performed using open loop steering evaluations at highway speeds and according to the Society of Automotive Engineers procedure J266, which includes testing to measure the steering required to follow a circular path at ever increasing speeds until the limits of tire traction are exceeded. The SAE J266 one hundred foot circle test was performed with both good tires and with a front or rear tire that had a totally separated tread and upper belt. In the tests with good tires, the vehicles could achieve a maximum lateral acceleration in the range of 0.65 g to in excess of 0.80 g in both clockwise and counterclockwise directions.

In this study, tests were performed with modified tires at the various front and rear positions on seventeen different vehicles to determine the effect of a full tire tread belt separation on a vehicle at highway speeds. The driver's steering and braking inputs were measured along with the vehicle responses during the event. The results show that the forces of a full tread belt separation generally do not force a vehicle out of a driver's control and that only small steering corrections are required to remain in the original lane of travel during the tread belt separation event. Additionally, forces due to the separating tires do not result in violent hop or tramp suspension responses during the separation event.

There have been several recent articles published concerning the effect of a tire tread separation on vehicle handling, but lately the literature has been silent on the situation where a tire airs out. This paper studies how various vehicles steer and handle during and after a tire deflates while the vehicle is traveling at speed. Utility vehicles, pickup trucks, and vans were tested by deflating front and rear tires. The air out condition was created by using a special test device that fired a twelve gauge shotgun shell at the sidewall of a tire while the vehicle was traveling at freeway speeds. The vehicles were instrumented with on board video equipment and a computer with transducers to measure both driver inputs and vehicle responses during the testing. The results show that a rapid tire air out creates a slight pull to the side of the deflated tire which then requires a small corrective steer to maintain a straight ahead course.

This paper explores tire placement with given tread depths on vehicles from two distinct perspectives. The first area explored is an analysis of crash data recently reported by the National Highway Traffic Safety Administration (NHTSA). In this report, thousands of tire-related crashes were investigated where the tread depth and inflation pressure were logged for each tire and assessments were made as to whether tire condition was a factor in the crash. The analysis of the data shows that in regards to accident causation, it is not statistically significant which axle has the deepest tread. What is significant is that a tread depth at or below 4/32″ anywhere on the vehicle leads to an increased rate of crashes. To understand the physics implied by the NHTSA data, a study was performed on how the placement of tires of various tread depths affects the steering, handling, and braking performance of a modern sport utility vehicle.

Recreational Off Road Vehicles (ROVs) which are sometimes referred to as side-by-sides, have increased in popularity over the last decade. These vehicles are available in many different sizes and performance characteristics from a host of different manufacturers and also have a variety of different missions, just as there are many types of off road terrain. The United States Federal Government, through the Consumer Product Safety Commission (CPSC), has advocated and proposed vehicle handling and rollover resistance standards for the side-by-sides which have a top speed above 25 miles per hour (these are not defined as “low speed vehicles”). For the sake of repeatability, the proposed maneuvers are to be performed on a high friction hard surface (like asphalt) as opposed to the off road surfaces (i.e. grass, sand, dirt, mud. rocks, etc.) that these vehicles are designed to be operated on.

Recently, papers have been published purporting to study the effect of rear axle tramp during tread separation events, and its effect on vehicle handling [1, 2]. Based on analysis and physical testing, one paper [1] has put forth a mathematical model which the authors claim allows vehicle designers to select shock damping values during the development process of a vehicle in order to assure that a vehicle will not experience axle tramp during tread separations. In the course of their work, “lumpy” tires (tires with rubber blocks adhered to the tire's tread) were employed to excite the axle tramp resonance, even though this method has been shown not to duplicate the physical mechanisms behind an actual tread belt separation. This paper evaluates the theories postulated in [1] by first analyzing the equations behind the mathematical model presented. The model is then tested to see if it agrees with observed physical testing.