Oct. 28, 2008 -- 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 6 vehicle may be suitable for one application and a Class 7 may work better for another.
A medium duty truck is not just any truck, it is the very foundation of your business contained in the truck body and for that reason you want the best. Medium duty trucks fall into the Class 5 (16,001 to 19,500 lb. GVWR), Class 6 (19,501 to 26,000 lb. GVWR) and Class 7 (26,001 to 33,000 lb. GVWR).
Know your payload, terrain conditions and body requirements and you'll be on the way to developing a good understanding of how to spec your medium duty truck chassis for your business application.
While the vehicle's GVWR is still important, buyers are increasingly focusing on other factors when making their selection, says Judy McTigue, medium duty marketing manager for Kenworth Truck Company.
“Customer expectations of medium duty trucks have continued to increase in recent years,” says McTigue. “Many users look for a business solution that provides superior uptime and reliability. An increased focus on fuel efficiency and efforts to reduce the environmental footprint are driving interest in hybrids, such as the Kenworth T270 and T370 straight trucks for pickup and delivery and utility applications and T370 tractor for local haul applications, including beverage, general freight and grocery distribution. Dependability is also high on the list because, day in and day out, medium duty trucks are work trucks and customer satisfaction is based on making timely deliveries, pick-ups, or service calls.
“For example, how many fires is it acceptable not to respond to because your town's pumper truck is down for servicing? Or how many missed residential propane deliveries are allowable in the dead of a cold winter?” asks Kenworth's McTigue. “Your medium duty truck must stay running because it's not easy to rent when it's down, unlike a tractor pulling a trailer. Think of it like a house. Your medium duty truck chassis is very similar – you need it to deliver your goods or services, each day, all day. You wouldn't build a house for your family on a foundation that will give way before the house itself.
“Buying the least expensive truck available from a body builder or dealer lot may seem like a good deal at the time, but in the long run it may be more expensive than the truck that was carefully spec'd,” says McTigue. “The medium duty customer's key concern should be life cycle cost and sometimes they learn too late what that means. Working with a dealer salesperson, a buyer can 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 life cycle cost.”
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.
Each medium duty application is different. Kenworth offers its T170 Class 5, T270 Class 6 and T370 Class 7 trucks that can be spec'd to fit various vocations. The Kenworth Medium Duty Body Builder Manual provides helpful information to mount the body correctly and with ease. “Bodies are mounted flush with the cab or with a space in between,” McTigue explains. “They can also be on top of the frame or extend below it. Kenworth's body builder options help the body builder with this process.
“Frame strength and length, can be determined when we 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, we need to have a better understanding of the weights and stresses that will be placed on the vehicle,” McTigue says.
“If it looks like the frame will be subject to a lot of stress, a larger frame size for a higher RBM (resisting bending moment) will be spec'd by Kenworth and may include an additional frame insert or heavy duty cross members. Applications that require higher strength frames include fire trucks, tankers and dump trucks.”
McTigue says Kenworth dealers use a special vehicle spec'ing software called Prospector(R) that makes it easier for a salesperson to put together the right spec. “We always review every order that comes in to make sure the spec will meet the customers requirement,” she adds. “Some clients want to over spec or under spec their vehicle. This won't necessarily improve the truck and may add to the operating costs and result in poor fuel economy and performance.”
Medium duty drivers often work a normal shift close to home. This is ideal for people new to the work force, students who need to work, or retirees looking for additional income. As a result, a truck's driveability has become a top priority for many buyers. A truck that is easy to drive and comfortable to operate will help control driver turnover.
Most medium duty vocations are not necessarily all about driving, says McTigue. “Take a look at fire trucks, refined fuels, mechanics, cranes, beverage, delivery vans, and so on. The person driving is a trained professional in some other field from fire fighter to retail salesperson first and foremost. The truck and body are simply tools of the trade. That's one reason why automatic transmissions have become very popular in all vocations,” McTigue 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 McTigue.
Numerous items factor into the vehicle's actual performance. Take, for example, turning radius. “The Kenworth T270 and T370 medium duty conventional models are standard with a 50-degree wheelcut to provide a tight turning circle. But 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,” McTigue notes.
“Longer wheelbases will also affect the turning radius. When spec'ing a unit, take into consideration the body and load carried in order to calculate optimal weight distribution and wheelbase,” McTigue 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 to carry additional weight.”
Cab access is more a function of truck design, but there are still choices. “The wider the steps and the less climbing drivers have to do to get in and out, the better,” says McTigue. “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.”
A final driveability issue is ride quality. McTigue says rear air ride suspensions are currently being spec'd on around 45% 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. Longer leaf springs on the front axle also help smooth and stabilize the ride,” McTigue says.
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 McTigue.
“In a fire and rescue application, you're going to need high horsepower and torque to get good acceleration. But in most pickup 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,” McTigue says. “An automatic or automated 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. “Pick something that will provide the startability needed 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,” McTigue concludes.