Tire wear and positioning considerations

Tires are one of the most critical components that need to be managed by vehicle fleet operators today. Not only can tires represent one of the largest maintenance issues, they also can have a significant effect on vehicle performance. Many existing...

Within moderation, most drivers can overcome or adjust to this phenomenon by introducing more steer input toward the desired direction of travel. All modern cars and trucks are designed with a natural amount of understeer built in through suspension configuration and basic weight distribution.

When a RAL occurs on the rear of both four- and six-wheel vehicles, the lateral vector induces an oversteering effect. Oversteer is the tendency of a vehicle to turn more than expected in the desired path.

This condition can be very unstabilizing for the average driver and can catch a person by surprise. Most drivers are not trained to correct for this condition and in extreme cases, can overcorrect and subsequently lose control of the vehicle.

The degree of RAL may be significantly different in four- and six-wheel vehicles. In the case of a four-wheel vehicle, the tendency of the vehicle to “kneel” in the rear is significantly higher than that experienced with a six-wheel vehicle. This “kneeling” effect results in a higher tendency to cause an oversteer situation.

Additionally, the lateral stabilizing capability at the rear of a four-wheel vehicle is effectively reduced by 50 percent. A six-wheel vehicle will experience a loss of only 25 percent.

Tire Placement

For U-Haul, customer safety is the number-one priority, and tire placement is predicated by the need to maintain vehicle control under diverse conditions.

For this reason, it is much more important to mitigate a RAL situation on the rear of a four-wheel vehicle than it is to mitigate it on the rear of a six-wheel vehicle. This condition reinforces the need to maintain the “best” tires on the rear of a four-wheel vehicle if at all possible.

As mentioned previously, six-wheel vehicles do experience a similar situation, but to a much lesser degree.

Furthermore, since modern vehicles are designed with a certain amount of overall understeer, a slight amount of oversteer caused by RAL on the rear of a six-wheel vehicle will result in minimal disruption of controllability.

For this reason, it is more important to mitigate a RAL situation on the front of a six-wheel vehicle. Consequently, it is desirable to place the “best” tires on the front or steer axle of six-wheel vehicles.

Based in Phoenix, Arizona, U-Haul International, Inc., is a North American equipment rental company. Since 1945, U-Haul has been the first choice of do-it-yourself movers, with a network of more than 16,300 locations in all 50 United States and 10 Canadian provinces. The U-Haul fleet is comprised of more than 104,000 trucks, 80,000 trailers and 36,000 towing devices.

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