For years, a key criterion for spec'ing medium-duty trucks has been the gross vehicle weight rating (GVWR). Users select trucks primarily on the basis of their class. So a Class 5 vehicle may be suitable for one application and a Class 6 may work better for another.

While the vehicle's GVWR is still important, buyers are increasingly focusing on other factors when making their selection, says Mike Parrish, medium-duty product marketing manager for Ken worth Truck Company.

"The expectations that people have of medium-duty trucks have continued to increase in recent years," Parrish noted. "Many of these truck users are looking for a business solution rather than just a vehicle. Dependability is high on their list because many are hauling perishable goods and they can't afford breakdowns.

"Buying the least expensive truck available off a dealer lot may seem like a good deal at the time, but in the long run it may be more expensive than one that was carefully spec'd. Their key concern should be lifecycle cost and sometimes they lose sight of that. Working with a dealer salesperson, a buyer should do a thorough analysis of how the truck will be used and then put together specs that will match the buyer's business goals and minimize lifecycle cost," Parrish says.

Consideration Number One: Body Wisdom

Some of the first things to consider are the type of load, annual mileage, and type of operating environment. Buyers can choose from a wide range of bodies that can be mounted differently depending on the truck's wheelbase and local weight regulations. "Bodies can be mounted flush with the cab or with a space in between," Parrish explains. "They can also be on top of the frame or extend below it.

"In order to calculate the correct frame strength, you first need to know the type of body selected. Typically, the big issue with a frame isn't just the kind of load, but also the body type and vehicle application. For example, there's no problem with a truck-mounted crane when it's traveling down the road mounted. But when it's parked and lifting loads, you need to have a better understanding of the weights and stresses that will be placed on the vehicle," Parrish says.

"If it looks like the frame will be subjected to a lot of stress, you can beef it up with inserts and/or go to a larger frame size for a higher resisting bending moment (RBM). Applications that require higher strength frames include fire trucks, tankers, and dump trucks."

Parrish says Kenworth dealers use a special vehicle spec'ing software called Prospector that makes it easier for a salesperson to put together the best spec. "We always review every order that comes in to make sure the spec is adequate," he adds. "Some clients like to over-spec, which adds cost unnecessarily and we discourage that. But we don't allow under-spec'ing."

Consideration Number Two: Driveability

With fleets finding it harder and harder to find drivers, a track's driveability has become a top priority for many buyers. A truck that is easy to drive and comfortable to operate is desirable.

This holds particularly true for vocations where the driver's main job is not driving, says Parrish. "Take a look at the beverage industry. The person driving is a retail salesperson first and foremost, and usually isn't being hired for driving skills.

"That's why automatic transmissions have become very popular in beverage. Between 80 and 90 percent of all the beverage trucks we build are spec'd with them. That compares to a 40 percent rate of automatics in all the medium-duty trucks we make," Parrish says.

Other important driver factors are startability, maneuverability, visibility, and ease of entrance and exit into and from the truck. "If your truck is going to be operated on busy roads, or there's a lot of loading and unloading in tight quarters, these factors become crucial," says Parrish.

Numerous items factor into the vehicle's actual performance. Take, for example, turning radius. If you need to get more weight up front, say for a crane application, you may need a heavier axle and larger tires and that could affect your turning radius, Parrish notes.

"Longer wheelbases will also affect the turning radius. When spec'ing a unit, you need to take into consideration the body and load carried in order to calculate your optimal weight distribution and wheelbase," Parrish says. "If it's going to be an inner-city truck, you may want to give up a foot or two in body length for better maneuverability. But if the truck will be doing a lot of highway miles and making few deliveries, you may want to extend the body length in order to carry additional weight." Visibility and cab access are more a function of truck design, but there are still choices.

"The wider the steps and the less climbing drivers have to do to gel in and out, the better," says Parrish. "Going to low-profile 19.5-inch tires can make life easier for a driver in an application with a lot of stop-and-go by helping to reduce fatigue. Well-placed steps are one key."

How well the driver can see to the front and sides is influenced by window area and the slope of the hood.

"Be sure to note how the mirrors are mounted. We mount mirrors on the cab rather than the door so the driver's view isn't blocked by mirror brackets. There's also less vibration and fewer problems with the mirror going out of adjustment every time the door is closed," he says. "For trucks spending a lot of time in-city or serving residential customers, such as propane delivery, there are numerous mirror options to fit the customer's specific needs."

A final driveability issue is ride quality. Parrish says rear air ride suspensions are currently being spec'd on around 30 percent of all Kenworth medium-duty vehicles.

"We see them in a variety of applications ranging from expeditors to dumps. A lot of it is how drivers prefer them for the smoother ride," he says. "But some maintenance managers don't want them because they feel they cost more to maintain than a leaf spring type. In general, if you don't need air suspension to protect the load, you can still get a good ride with a leaf spring" type. In general, if you don't need air suspension to protect the load, you can still get a good ride with a leaf spring."

Longer leaf springs on the front axle also help smooth and stabilize the ride.

Consideration Number Three: The Drivetrain

A carefully spec'd drivetrain can lower your total operating costs over the truck's life. Be careful not to over-spec the engine, says Parrish.

"In a fire and rescue application, you're going to need high horsepower and torque to get good acceleration. But in most pick-up and delivery applications, you aren't going to need nearly the same amount."

Your transmission choice is primarily based on performance requirements and driver ability. "A manual transmission may be best if you either have an experienced driver or don't make frequent deliveries," he says. "An automatic transmission may be a better fit if you either have a new driver or routes with frequent stops."

Whether you select manual or automatic, you should choose the rear axle ratio carefully to get the best fuel economy. "You need to pick something which will give you the startability you need based on the load that will be carried, but also keeps the engine in the most fuel-efficient operating range as long as possible. As it is with many of the other specs, it all comes down to finding the right balance," Parrish concludes.