The Car and Truck Fleet and Leasing Management Magazine

Overloading is the No. 1 Cause of Unscheduled Truck Maintenance

April 2007, by Mike Antich - Also by this author

Overloading creates an unsafe vehicle and increases liability exposure. When a vehicle is overloaded, its emergency handling capability is reduced, which can contribute to an accident. For instance, braking distance increases, which can cause drivers to misjudge stopping distances, and tire failure rates are higher because tires run hotter. Overloading is also expensive. In fact, fleet maintenance surveys consistently show that overloading is the No. 1 cause of unscheduled maintenance for trucks.

Oftentimes, fleet managers themselves are responsible for overloading by under-spec’ing a truck for its intended fleet application. This is particularly prevalent with light-duty fleets. “Since DOT regs start at 10,001 lbs., some fleets try to avoid driver logs, hours of service, and physicals by keeping vehicles under 10,001 lbs.,” said Mike Sturges, national truck sales manager, Southern Zone for ARI.

Fleet managers should avoid modifying under-spec’ed trucks to accommodate greater payloads, such as changing tire sizes, adding spring kits, air shocks, heavy-duty brakes, and anti-sway kits. In many ways, these modifications are self-defeating. These components can add significant weight to the chassis, which reduces the available payload by several hundred pounds. However, the key reason to avoid modifying a vehicle is that it creates an unsafe situation by changing the integrity of the vehicle. In addition, modifications may result in warranty claim denial and increase liability exposure if there is an accident.

“It is important to note that modifications to gross vehicle weight can only be made by the OEM,” said Ron Ice, truck specifications engineer for PHH Arval. This caution is seconded by Bill Byron, senior truck specialist for Donlen Corp. “Fleet users need to remember that frame strength, spring strength (either leaf or coil), brake pads, rotors, and tires have all been engineered, designed, and tested by the manufacturers to perform within a particular stress environment,” said Byron. “When that environment is amended, those weakest links are asked to outperform their design function and the result is typically a component failure.”

Another prevalent problem is axle overloading. Even though a vehicle’s payload may be within limits, the vehicle may still be overloaded on one of its axles. “Keep in mind that estimated available payloads are figured assuming a liquid or level load. It is possible that a front or rear axle is overloaded with only a portion of the maximum payload on the truck,” said Steve Swedberg, truck engineering & ordering specialist – vehicle acquisitions for Emkay Inc.

This caution is also stressed by Bob Shipp, national truck sales manager for ARI. “Load distribution is the key to avoiding axle overloading. Vehicles can be under the total GVW, but, because of improper loading, may be over the GVW of one of the axles. You eliminate rear-axle overloading using an interior package or body configuration that forces placement of heavier items forward of the rear axle. This can be achieved using specific locations for specific items with slots, tie downs, and shelf location,” added Shipp.

One way to detect axle overloading early is to require fully loaded vehicles to be regularly weighed at a weigh scale. “While at the weigh station, the front- and rear-axle weights should be noted. Just because the truck may not be overloaded as far as total GVWR, either axle may be overloaded. For instance, if the rear axle is carrying more than 90 percent of the total load for a conventional cab chassis, the front axle does not have enough weight on driving surface.

This can cause premature wear and tear on tires and suspension components. It also affects the driving characteristics of the vehicle,” said Sturges. In lieu of taking a vehicle to a weigh station, another way to recognize an overloaded axle is to inspect the leaf springs on the rear axle. “Leaf springs are arched upward. If they are flat or arched downward, your load maybe riding on the axle,” said Shipp.

Overloading is Dangerous
A good rule of thumb to avoid overloading is to overspec for a fleet application. “Build a 15-20 percent cushion into a vehicle’s payload capacity,” said Mike Corchin, manager of truck business development for Wheels Inc. Also, involve end users in spec’ing vehicles. “Communicating with the actual end user provides valuable payload information requirements and user-friendly upfitting desires,” said Byron. “Today’s vehicles are competitively priced, so moving within a model line to provide for greater payload capability will generally result in a very modest price increase.”

Another way to minimize overloading a vehicle is to eliminate unnecessary equipment or shelving. Carry only needed items. If given the opportunity, drivers will carry everything they can conceivably fit into a vehicle. “Companies should have specific guidelines as to what can be carried in vehicles both in terms of tools, passengers, and types of payload,” said Corchin.

It is crucial to communicate to field employees the dangers of overloading. “The manufacturer of the truck sets the GVWR according to what the vehicle can safely stop, carry, and perform at an acceptable level. Failure to consider payload and weight distribution may result in failure of equipment, personal injuries, and possible liabilities,” said Ice.

The bottom line is that overloading is extremely dangerous.

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Michael Sims is fleet operations manager for the Church of Jesus Christ of Latter-Day Saints.

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