Chapter 4 -
Developing vehicle specifications

An objective in developing specifications is to create an environment of competition without “wiring” a specification for one make and model.

Most heavy-duty vehicles are a mixture of many subcomponents supplied and assembled by a manufacturer. Light- and medium-duty vehicle components generally are produced by a manufacturer that coordinates subassemblies under one name. Often, brand preference is due to buyer confidence in a particular manufacturer’s assembly process. Competition, if managed objectively, produces the best value.

If you typically work with a local dealer that provides convenient, reliable and cost-effective service, you still may want to solicit bids from dealers that sell the same or other brands. Then you can compare dealers’ service efficiency. Cross-reference each vendor, line item by line item, to resolve cost variances — not only in unit prices, but also in component costs.

Another consideration to include in the specifications is spare parts. Specifying which spare parts you may need will allow in-house support organizations to keep these consumables and fast-moving items available for servicing vehicles.

Include “birth certificate” information that lists the original specifications for record-keeping and accurate parts replacement. A parts line sheet usually is included with a chassis delivery. It lists the original equipment manufacturer’s part numbers for use in ordering. Be sure that each line item is typed with a standard part number. If you find handwritten or blank items, research the reason. The component could be a one-of-a-kind — which makes replacement virtually impossible.

Many trucking companies use computerized records. Computerization provides accurate cost systems for inventory but requires accurate and timely input. Data should be input upon receipt of the vehicle, for future reference. Require all manufacturers to provide the forms just before the vehicle is delivered.

When you take delivery of the vehicle, verify the information from the manufacturer. After verification, enter the data for vehicle service into your system.

Today more than ever, fleet managers must review use patterns with drivers, dispatchers, purchasing personnel and customers before writing equipment specifications. Determining their needs beforehand can increase productivity and efficiency, and help ensure that the vehicle you purchase is the right one for the job.

Operating requirements
Selecting the right vehicle requires thorough knowledge of operating requirements. Before purchasing a new vehicle, define and draft a specifications list. With the help of qualified personnel, you may elect to write the specifications list. Another option is to use the expertise of knowledgeable sales people and engineers at dealerships or factory branches.

It is wise to review specifications with experienced manufacturer salespeople. After careful study, you can give a standard bid request to each supplier, requesting an accurate bid on identically equipped models. Written vehicle specifications eliminate the possibility of verbal misunderstandings.

Study fleet requirements first. Know what the trucks will haul, whether any backhauls will be required, how products will be shipped, what the loads will weigh and what the maximum weight per trip will be. What are the cargo’s dimensions? How many cubic feet, cubic yards or gallons of carrying capacity are needed? Select a chassis that can handle the average load, but that also offers sufficient capacity for the occasional load that exceeds the norm. This consideration can help with resale.

Loading characteristics influence specific component selections, especially horsepower requirements, gearing and suspension systems. Determine whether the vehicle will carry full loads both ways or one way, partial loads, or diminishing loads. Make sure that the vehicle meets two requirements: (1) It can carry the load, and (2) it can move the load.

Carrying the load
The weight distribution on the front and rear axles depends on the cab and chassis configuration. Conventional cabs have 20 percent to 25 percent of the weight on the front axle.

A truck’s gross vehicle weight is the sum of the weight on the front and rear axles. Each vehicle must comply with state law. The number and spacing of axles dictate the weight that can be carried on each axle. More axles mean less weight on each axle and, correspondingly, less on each tire. Better weight distribution translates into less wear and tear on the road.

When selecting a vehicle, carefully study the gross vehicle weight to ensure that it is properly distributed. Correct distribution of weight to the axles provides the most comfortable ride, increases steering control, and maximizes driving and braking traction. It also guards against premature failures due to overloaded springs, axles and tires.

Computer-assisted design identifies components and their assembled weight. Ask bidders to submit a weight-distribution analysis with the bid. When the vehicle is delivered, weigh it to ensure that it matches the specification calculations. Compare this weight to the certified weigh-in and verify the final weights. Do not accept the vehicle unless it checks out.

The vehicle must be weighed while fully loaded, one axle at a time (front, drive and trailer axles). Make sure the axles, wheels/rims and tires provide sufficient carrying capacity. Also establish proper air pressure for all axles. Label the vehicle with the proper air pressure for each set of axles. You can affix a sticker or paint this information on the vehicle.

If the weights are not accurate, refer the problem to the manufacturer for correction. If the weights are not corrected, you have the option of rejecting the vehicle.

Moving the load
The vehicle’s engine is the heart of its efficiency. If horsepower is too low, expect subpar performance, premature failures and high repair costs. Buy an engine with too much power, and you’ll spend more for poorer fuel economy and no extra benefits.

Most engine/transmission combinations in medium- and heavy-duty trucks provide sufficient power and gear reductions for adequate performance. Although performance cannot be ignored in the selection of components for light trucks, it is not as critical as it is for heavier units.

To move a load, a vehicle must have an engine that can supply adequate power. It must have the proper transmission and rear-axle ratios to transmit power to the rear wheels. For maximum performance, consider several factors:

• Maximum gear reduction. This factor provides the greatest multiplication of torque in a given powertrain. The highest reduction occurs when the transmission is in its lowest gear. Vehicle starting capability is directly affected, and measured, by maximum reduction. Trucks operated in on- and off-highway service or in hilly areas usually require greater reduction than units operating on Interstates. As gross vehicle weight increases, greater gear reduction (or more power) is required.
• Geared road speed. This factor is the maximum speed that the vehicle attains when the transmission is in top gear and the engine is operating at its top-governed rpm. Geared road speed is limited by gear ratios and governed engine speed. Many vehicles, especially heavier units, cannot achieve geared road speed because it requires more horsepower than is available.
• Gradability. This factor is the measure of a vehicle’s capability to start on and climb an incline. Gradability is indicated by percent of grade. A 1 percent grade, for example, is equivalent to a 1-foot rise over a distance of 100 feet. A vehicle must have a minimum of 10 percent gradability to set it in motion from a standing start on flat ground. The unit also must have sufficient gradability to negotiate the steepest grade encountered. If a unit encounters an 8 percent grade (a rise of 8 feet over 100 feet of travel) on its normal route, a minimum of 18 percent gradability is required — 10 percent starting and 8 percent operating.
• Speedability. This factor is the actual road speed a vehicle can attain on flat ground in still air. Speedability is influenced by an engine’s capability to overcome the combined retarding effects of gross weight, air and road resistance. Speedability should equal or exceed the vehicle’s geared road speed. With today’s high gross weights and road speeds, vehicles require significant horsepower to keep up with traffic and get good fuel economy.
• Gear steps. This factor involves transmission selection. Transmissions vary from three to 20 (or more) speeds. Specifying the right number of gears is important. Even if 20 speeds are available, if seven can do the job, the seven-speed transmission is preferable, because it is easier to drive and more economical.

Evaluate routes as well. For what type of service will the truck be used? Will it be used on city streets or open highways? Mileage covered and hours of operation also are important. How many miles will the vehicle cover per day, per week or per round trip? How many stops will the truck make per day?

Consider the terrain in determining horsepower needs and gear ratios. Determine the maximum grade that the vehicle must negotiate. Does the route have an inclined loading dock or some other steep incline in an unlikely place? Specify vehicles for the terrain in which they will be used, even if you buy them in another city or state.

Starting capability is a critical factor. Reliable starts are as important for local trucks with limited expressway use as they are for long-distance highway vehicles.

Trucks that will be used primarily at night have greater electrical and charging-system needs and require more lights than those used mainly during the day. Note any unusual operating situations — such as extreme temperatures, high altitudes, narrow streets and low bridges — in the specification.

In Summary
When spec’ing a vehicle, one of the main considerations is its ability to carry and move the load. To ensure the vehicle can carry the load, carefully study its gross vehicle weight to ensure it is properly distributed. Consider serveral factors — maximum gear reduction, geared road speed, gradability, speedability and gear steps — to ensure the vehicle has the performance characteristics necessary to move the load. Other considerations include the route and terrain over which the vehicle will travel.