Spec’ing a medium-duty truck can be a daunting task. Trucks must be equipped to handle very specific fleet applications, which require specifying a multitude of components such as the right drivetrain, suspension, and body.

“Many truck users lack the requisite technical expertise to engineer and develop vehicles that are properly suited to the requirements of the job,” said John Riordan, director – Truck Engineering/Purchasing for CitiCapital Fleet in Carrollton, TX. Unless you, as the fleet manager, understand the fundamentals of truck spec’ing, you cannot properly manage the specification process and provide the best vehicle for your fleet application.

Here is a four-step explanation to help you learn the necessary questions to ask in order to spec the right truck for your fleet application.

Step 1: Understand Your Truck Needs

The first step to correctly spec’ing a truck is to meet with the drivers or technicians who will be using the vehicle. By understanding their day-to-day application, you will be able to build a truck that meets their needs.

“Vehicle specifications should be defined by the application and mission requirements,” said Rior-dan. “Input should be solicited from field personnel to ensure that local issues affecting the vehicle’s operation are taken into account,” added Riordan. In particular, the fleet manager needs to understand what type of service the truck is expected to perform.

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Agreeing is Jeff Robley, national truck sales manager for ARI in Minneapolis. “You need to talk with the people in the field to understand where the trucks are driven and how they are used,” he said.

Sometimes this information can be gathered over the phone; however, more complicated applica-tions may require a site visit. The key objective to these discussions is to match the truck with the fleet application. When meeting with your end-users, ask questions about their current vehicles. For example:

 Is the powertrain right for their application?

 Is the gross vehicle weight adequate for the payload carried?

 Is there enough gross combination weight rating (GCWR), if the vehicle will be towing a trailer?

Look at the existing truck and investigate the maintenance records. What type of problems has this truck had, if any? This will help you determine if the current vehicle has been under-spec’d. If it has, then take the necessary steps to correct it. The majority of trucks that have problems are under-powered and overloaded, which results in increased downtime.

Analyze your maintenance records to see what mileage, and at what time intervals, your present trucks have needed major servicing such as a brake re-line, new or re-capped tires, and engine work.

Talk to the employees who are using your trucks. They may have problems with loading height, cab access, lack of bins, difficulty when backing, or insufficient tool storage, said Wayne Reynolds, maager, corporate fleet trucks for LeasePlan in Atlanta. “Ask them about passenger requirements, whether there is going to be a high idling requirement, how the payload will be distributed, whether the vehicle will be fully loaded, or whether it will be operating with a diminishing load, and how they load and off-load cargo,” adds Reynolds.

Consideration should also be given to whether a liftgate or pull-out ramp should be chosen for the truck body, said Robley. “Ask how will you load your payload? Will you use handloading, pallet jacks, or forklifts? What are the dimen-sions of the payload?”

It is important to design a truck that will accommodate your operational requirements rather than trying to make your operation conform to the truck.

“When you’re spec’ing a medium-duty truck, there are a number of key factors that have to be gotten right, or you’ll make an expensive mistake,” said Ronald Ice, specifications engineer for PHH Arval. “The foremost consideration has to be the payload. How much does the cargo you plan to carry weigh? We’ve found that people often have no idea what the payload will be – and that means trouble. The weight of the payload determines the engine, transmission, size of tires, frame – just about everything.”

After compiling the input you have gathered from the field, you must next review budgetary consid-erations. One factor that can sway the decision on which chassis to acquire is a manufacturer’s incentive program.

The type of truck your field personnel would like may not always fit into the annual budget.

“Although first cost is a major consideration, it is essential that maintenance and other operating costs, along with projected residual value, be factored into the selection decision,” said Donovan "Whit" Ford, senior truck engineering specialist for CitiCapital Fleet.

It is a balance between over-spec’ing and under-spec’ing a vehicle and each presents its own unique set of problems. Over-spec’ing a truck increases the capitalized cost of the vehicle, while under-spec’ing increases maintenance cost. In addition, an over-loaded vehicle puts your company at risk of a lawsuit if it is involved in an accident.

“There is a tendency to under-spec trucks to avoid exceeding the 26,000-lbs.-GVW threshold, which requires drivers with commercial driver’s licenses and compliance with increased regulatory requirements,” said Terry Crawford, senior truck engineering specialist for CitiCapital Fleet. “There are many potential ramifications that may result from this, including overloading, the requirement for multiple trips due to limited payload capacity, and the employment of inexperienced or unqualified drivers.”

Another consideration, according to Reynolds, is to understand how a vehicle will be loaded and un-loaded. Know the height requirements of the truck. “For instance, what is the dock height? Sometimes, there may be a non-standard dock height,” said Reynolds.

Adds Regan Mullikin, medium/heavy-duty truck specialist for LeasePlan: “If a forklift is util-ized in the loading or unloading process, it is essential to have the forklift reinforcement option included in the body specifications. Also, know where and how your drivers are securing the load. Take into consideration the height and bulk of your product to ensure your truck has the proper cargo restraint system.”

Step 2: Determine the Payload

Payload is probably the most critical aspect of truck spec’ing.

“A common problem by inexperienced fleet managers is that they do not know the truck’s operating parameters and its payload requirements,” said Robley.

There are three main components to determining the payload requirement.

The first component is payload weight. How much weight will the truck need to carry in its daily workload? You need to figure the maximum need here, not an average. The vehicle must be able to do the job every day with the maximum load at any given time.

“Payload weight will also help determine if the cargo can be loaded and unloaded by hand or whether you will need a power liftgate or some other type of assist to get it up in the body or bed,” said Robley.

“Another area where it’s important to get it right is in the volume or size of the payload,” said Ice. “The truck needs to be large enough to handle the volume. And you need to know how the payload will be loaded. Is it stackable? Can you stack it right to the ceiling? Or, can only the floor space be used? How do you secure the product? Getting any of these factors wrong can mean the vehicle will be spec’ed incorrectly.”

The third component is the actual type of payload. Are you going to carry loose gravel, pallets, or boxes of merchandise? This will decide the type of truck and body combination you need to choose.

“The best way to determine actual payload is to take a truck as it would be normally loaded and weigh it on a highway scale,” said Reynolds. Another practical tip is to also weigh the front axle and rear axle. This will tell you if you are overloading the whole truck or just one of the axles.

“By determining the fleet application, you will determine the payload. The single most important factor in selecting a truck is determining the payload needed to perform a particular operation,” said Robley. Overextending a truck’s payload capacity beyond the chassis’ weight specifications is a good way to shorten the truck’s service life. “If you don’t spec the vehicle to the correct payload, you will run into mechanical issues down the road,” said Reynolds.

Overloaded trucks will cause problems such as premature tire wear, lost miles per gallon, and downtime due to engine or transmission repair.

In addition, overloading may put you in trouble with the law. Overloading results in fines from the police and possible impoundment of the vehicle by the authorities. Also, there is significant company exposure to lawsuits should an accident occur.

You need to make sure that the truck can carry not only the payload but also any additional equipment you put on the truck. The fleet manager needs to add the body and equipment weight to that of any tools or other material that could be stored or transported by the chassis.

Step 3: Select a Chassis

When selecting a chassis, it is important to know the proximity of local dealers and service facilities to your fleet operation. “Who in your area can service medium-duties? What dealers are nearby? You need to know this in order to get warranty work done,” said Robley. “It doesn’t make sense to acquire a nameplate which doesn’t have a nearby dealership.”

However, one of the most important aspects in determining the criteria for choosing a truck, is the gross vehicle weight rating or GVWR. This rating reflects the maximum GVWR a particular truck is certified to carry. This rating consists of two weight factors: the empty vehicle (curb weight), and the payload it will carry (the con-tents to be hauled, the passengers/driver, and fuel).

To determine the correct size of a vehicle for the intended payload often requires a non-scientific judgment call: namely, how much over-capacity to build into the payload capacity of the vehicle when spec’ing its requirements. Spec’ing the truck to the minimum necessary payload rating (by basing it on an average load, or looking at only today’s business needs instead of trying to anticipate future needs) means that the vehicle will be operating at peak capacity most of the time, which may compromise safety and the length of its service life. Using average payload for specs means that the vehicle will sometimes be overloaded – and that means excessive wear and tear, higher maintenance costs, and poor fuel economy. At the same time, too much payload capacity is wasted capacity that should be avoided.

One of the most common mistakes made by fleet managers is not understanding the importance of allowing reserve GVW when spec’ing a truck. Some items to consider when determining how much reserve GVWR is necessary include the wheelbase, axle rating, the type of body, and the type of application. Generally speaking, there should be approximately 20 percent reserve GVWR.

GVWR alone, however, does not tell what class or size of truck is needed. How the cargo is distrib-uted is also extremely important, and partially determines gross axle weight rating (GAWR), which identifies the maximum load-bearing limit of a complete axle and suspension system, made up of wheels, tires, and springs, but not shocks. Essentially, GVWR is determined by the lowest rating of a truck’s load-carrying components, which include the frame, springs or suspension, axles, and tires. For the most part, shock absorbers are not included in an axle’s weight rating, since they are not designed to carry weight. The weakest link among these components, usually tires, determines the GVWR rating.

The GVWR and GAWR cannot be exceeded without risking some serious problems, such as steering and handling problems, excess wear, and reduced vehicle life. The converse is true as well; it makes no sense to over-spec a truck, because the vehicle will inevitably incur higher operating costs because the truck is under-utilized, causing a fleet to pay for more ca-pacity than it needs.

Another consideration is regulatory requirements.

“If a truck is more than 10,000 lbs. GVW, then it is subject to DOT regulations,” said Robley. “If you are crossing a state line, you are also subject to DOT. You need to check the state laws, because most states have adopted DOT standards. If you are transporting hazardous materials, then your driver needs to be licensed properly. If you go over 26,000 lbs., then your driver needs a CDL. If you have air brakes, then you need an air brake endorsement. If you go over 33,000 lbs., then you are subject to a 12-percent federal excise tax.”

Step 4: Selecting the Powertrain

Once the size of the chassis has been determined, it’s time to think about powertrains. The powertrain is made up of the engine, transmis-sion, driveline, rear axle, wheels, and tires.

The first thing to consider when selecting a powertrain is the operating conditions and performance criteria, said Reynolds.

This involves nine factors:

1. How will the truck be used?

2. Typical GVW.

3. Annual miles.

4. Expected operating surfaces.

5. Desired cruising speed.

6. Desired startability.

7. Desired high gear gradeability and cruising speed.

8. Vehicle configuration, such as number of drive axles and tires.

9. Operating altitudes and temperature.

The speed you expect your truck to travel is also an important consideration. Will it be stop-and-go city driving not exceeding 55 mph or will it be at highway speeds? Knowing this will help you determine what engine, transmission, and axle ratio you will need.

A truck’s engine horsepower requirement is determined by the desired road speed at which the load should travel. This establishes the guidelines to select the right engine and transmission, which is important for minimizing overall operat-ing costs. The proper engine and transmission selection must achieve a balance between operating economy and vehicle performance requirements.

“It’s important to analyze where the vehicle will be operated. If the geographical location is mountainous or hilly, you’re going to need to spec the vehicle accordingly. If it’s in flat territory, you can get by with less truck,” said Ice.

By determining the speed at which a load should be moved, another fundamental guideline, final axle ratio, is determined. Rear axle ratio selection is based on two major factors: the desired road speed and the governed engine speed. This can be used to calculate the best ratio to get a vehicle to the required maximum speed. How fast and under what conditions the load must be moved will also have a direct bearing on the final drive ratio’s requirements. The final drive ratio is simply the number of revolutions the drive shaft makes compared to the turns of the drive wheels. A 4.10:1 ratio means that the drive shaft turns 4.10 times for every one revolution of the drive wheels. Higher ratios usually mean better startability, gradeability, and towing capability, but at the expense of a lower top speed. Higher ratios make sense for fully-loaded trucks operating in congested urban conditions, or those that must negotiate hilly or steep road conditions.

Typically, when road speed rises, there is a corresponding reduction of torque, which requires a lower axle ratio. An axle ratio selection chart indicating various governed engine speeds can be used to determine the correct rear axle ratio.

You must consider three things when determining what axle ratio to use. Those are:

1. What is the steepest grade your truck will go up?

2. How fast do you want your truck to go?

3. Will this truck be operating in on- or off-road applications?

Off-road operating requirements might call for a different suspension, or different transmission-rear axle ratio combinations.

Also, determine whether there will be an increasing or decreasing load throughout the workday. Will the engine/transmission/axle ratio support the payload, allow for trailering if needed, and be compatible with strict federal emission requirements?

There are, of course, other factors in powertrain selection such as engine rpm, torque efficiency, engine governors, number of transmission speeds, and transmission ratios; but the fundamental re-quirement – speed – establishes the guideline from which these specifications are developed.

Transmissions are a key power-train component. Transmission choices vary from four- to 10-speed manuals to five-speed overdrive automatics.

The terrain a vehicle will travel will help determine the type of transmission.

If the truck will be doing highway miles, then you will want to match it with a higher rear axle ratio and a transmission with as many forward gears as possible to achieve maximum fuel economy. If you will be driving the truck in hilly country, you will want a lower rear axle ratio with fewer gears to provide more torque.

One factor prompting fleets to specify automatic transmission is that there are not as many drivers today who can operate a manual transmission as in the past.

“Recently, I find that many fleets are opting for automatic transmissions, especially if initial cost and availability are not overriding issues,” said Reynolds.

Manual transmissions cost less to purchase and repair, but in the long run, automatics can be easier to operate and don’t have clutches to replace.

If your fleet application requires the use of a power take-off, it could dictate an engine power modification. A power take-off, or PTO, is a device usually mounted on the side of the transmission or transfer case or off the front of the crankshaft and is used to transmit engine power to auxiliary equipment such as pumps and winches.

Spec’ing Checklist

1. Meet with drivers to understand their needs.

2. Analyze maintenance records of existing trucks.

3. Determine payload requirements.

4. Determine volume and size of payload.

5. Select chassis where dealers and service facilities are in close proximity to fleet operations.

6. Select a powertrain based on operating conditions and performance criteria.

7. Engine horsepower is determined by the desired road speed at which the load should travel.