Accessory equipment

Scope

All carriers need to consider what accessory equipment they want on the vehicles they spec.

Regulatory citations

• 49 CFR 393 — Parts and accessories necessary for safe operation
• 49 CFR 393.3 — Additional equipment and accessories
• 49 CFR 393.22 — Combination of lighting devices and reflectors

Key definitions

• Accessory equipment: Additional, non-required equipment and accessories added to a vehicle by a manufacturer or vehicle owner. These are also referred to as “options.”
• Required parts and accessories: Parts and accessories required in the Federal Motor Carrier Safety Administration regulations and the National Highway Traffic Safety Administration standards.

Summary of requirements

There are many options that can be added to a commercial vehicle. Listed below are some of the most common a carrier should consider adding:

• Air dryers reduce water, oil, and carbon contamination; the curse of any air-braking system. They operate on the principles of condensation, use of a drying agent (desiccant), or centrifugal force to clean and dry the compressed air before it is delivered to the system. If you think an air dryer might help reduce brake problems, check to see what additional maintenance will be involved with servicing this component.

• Engine braking has become more important because today's fuel-efficient truck models roll more easily and the new fuel-efficient engines have reduced natural engine-braking ability. Retarders fill the need for additional engine-braking; they spare the braking system, while allowing the driver to control the retarding power. They fall into four categories:
  • Exhaust retarders have a control which closes the exhaust pipe, thereby creating back pressure in the exhaust system to slow the engine.
  • Engine retarders and engine brakes change the valve timing or injector functions in the engine, thereby limiting the number of cylinders working (the venerable Jake brake is of this type).
  • Hydraulic retarders cause the engine to work against a fluid system contained in a closed housing that is part of the transmission.
  • Electric retarders consist of electromagnetic coils which produce a drag force on the truck's driveline or trailer axle.

• Maintenance-free batteries require less frequent checks for water levels, reduce actual water loss from the cells, and minimize corrosion. Whatever the choice, price should not be the only consideration. Vibration test information can be an important key to how long a battery will last, yet one manufacturer reports that fleets seldom request this information when considering a brand. A new container material, structural foam polypropylene, is available in addition to the usual hard rubber and thin-walled version. This newer material weighs less and seems to offer better resistance to vibration.

• Fuel heaters can keep the fuel flow going smoothly. Choose a mechanically simple model that heats the fuel before it goes into the first fuel filter and also prevents overheating of the fuel. Since the primary fuel filter and its supply line are the most common component affected by cold weather, it may be helpful to choose a model located in the engine compartment. Avoid those mounted outside the frame rails where they are exposed to wind.

• Water separators can be used in combination with a primary fuel filter or separately, to keep water and other contaminants in fuel from reaching the engine. Since they must be drained regularly to prevent freezing, be sure they're conveniently located.

• Aerodynamic accessories can significantly increase fuel mileage. Air resistance is a truck's second greatest impediment to movement, and therefore optimum fuel economy. Only weight impacts miles per gallon more. Efficient aerodynamics smooths the flow of air over, under, and around the vehicle. It is not uncommon for some aerodynamic vehicle designs to save carriers as much as 4-5 cents per mile in fuel savings. Aerodynamic accessories include:
  • Cab extenders, designed to bridge the gap between the truck cab and the trailer.
  • Side-skirts cover the fuel tanks and battery box, smoothing out the overall profile of the truck.
  • Air-dam front bumpers and aerodynamic hoods, which are designed to ease air flow around the front of the vehicle.
  • Other aerodynamic accessories (or aerodynamic location of accessories), such as mirrors, air intakes, air horns, and grab handles.
  • Trailer air deflectors including nose and rear "bubbles," side skirts, and axle air deflectors.
  Any of these options can increase fuel economy by 1-3 percent.

• Tire size does matter since a truck's overall gearing changes with the diameter and circumference of its tires. Tread type also impacts fuel economy, since a tire's tread helps determine rolling resistance. For example, a lug-type drive-axle tire in winter will improve traction, but will also lower fuel economy by 2-4 percent. Tire technology has improved dramatically recently. With improvements in tread designs, casting designs, rubber compounds, and friction reduction, definite and significant savings can be realized by spec'ing the right tires for your equipment.