Spec’ing a truck is an interesting exercise indeed. It takes a measure of discipline and honesty, as well as a thorough understanding of what you plan to do with it. Owner-operators have an extra layer of complexity to deal with by sometimes having to spec for several different operations – that is, unless you plan to stay where you are for the life of the truck.

How well you spec the truck in the first place, and how closely you operate the truck to the spec you laid out, can mean the difference between eating cat food for five years, and having enough in your jeans at the end to hand over a substantial cash down payment on the next truck.

That’s the way Derek Varley calls it. He’s the fleet manager at Mackie Moving Systems in Oshawa, Ont. He’s a student of the art of truck spec’ing, and he’s pretty good at it by all accounts.

His pride and joy is a truck on a dedicated run from Oshawa, Ont. to Pittsburgh, Pa., running Highway 401, the Queen Elizabeth Way, I-90, and I-79, averaging a 35,000- to 40,000-lb payload downbound and 15,000 lb back. The truck has been on the run for a year, and Varley reports it’s doing an impressive 8.5 mpg U.S. The spec is a Cummins ISX 450, a ZF Meritor FreedomLine 12-speed automated tranny with 0.83 overdrive gearing, and a 3.55:1 rear axle ratio.

Varley says owner-operators who are stuck on the big-power spec are often overbuying, and paying twice for the mistake: once on the bill of sale, and again at the pumps.

“It’s like buying a $400,000 house and leaving all the windows and doors open all summer with the A/C running full out,” he says. “That’s what they’re doing with the big engines on a tandem run.”

The Puzzle:

Is there an ideal spec? Yes, but don’t expect Varley’s spec, or your buddy’s, to necessarily work for you. There’s a lot to consider, not the least of which is getting over the “build-me-what-I-had-last-time” mindset. Mark Wille, sales manager at Mississauga’s Peel Mack, hears that a lot. “Trouble is,” Wille notes, “we don’t make trucks like that any more.”

A lot has happened in truck engineering over the past five years. If you’re on a five-year cycle, you’re looking at a whole new spec to meet today’s engine operating parameters.

For example, Trent Siemens, maintenance manager at Big Freight Systems in Steinbach, Man., says three years ago his fleet standard rear-axle ratio was 4.33. Today he’s running 3.55s in the tandems and 4.11s in the B-train fleet. They were running Cummins N14s at the time, which wanted to run 1680 rpm at 62 mph. By comparison, Cummins’ newer ISX engines are happiest at 1450 rpm in tandem service. The gearing had to change.

“The engines need to be turning more slowly today, thanks to the emissions rules,” Siemens says. “If you spec outside that engine-speed envelope, it’s going to cost a fortune.”

So where do you start? You have to bring three things to the table at once, right from the start: your intended application (tandem or heavy), the terrain you plan to run on (flat, hilly, mountainous, or a combination), and your intended cruise speed. Your power requirements will depend on all these factors. But before you choose an engine, you need to determine how it will operate. For example, will it be pulling heavy loads in the mountains or light loads on flat ground? An engine pulling heavy will necessarily need more horsepower than a lightly loaded one. Hills will demand a higher gear ratio (4.11 or 4.33:1) for decent and efficient performance on the grades. Flat ground allows for lower gears and reduced engine speeds (3.36 or 3.55:1).

Dealerships have software programs that help you work through all this, but you have to know what you’re doing when you sit down. Cummins has an on-line spec’ing program called “PowerSpec” that takes you through this process, explaining each step as you go. The result of the spec you feed in will come back acceptable or not, and the program notes will explain why. Check out www.powerspec.
cummins.com.

“You need to have an idea of what you want, then the simulator can run what you’ve built in simulation. You come in with the application and the speed you want to run, and the sales rep will walk you through the rest,” advises Jeff Van Pouke of Cummins Canada.

Several other factors affect the speed you run the engine, such as tire size, your transmission preference, and its final drive ratio. In addition, load factors and torque curves will also affect the final spec.

This is all nuts and bolts stuff, so far. You’re trying to determine the demands on the operation, and the optimum operating conditions. Once you’re this far you can start playing around with engine specs. And don’t fool yourself. There’s more than color separating one engine brand from another.

There’s more than one way to spec a truck. Each represents an intelligent compromise of power and speed, but all three yield the same result: money in the bank.

There’s a lot at stake in making the right choice. Fuel is the single biggest expense owner-ops have, but as David McKenna, Mack Truck’s product marketing manager, points out, “Fuel is your single biggest controllable expense. If you want to keep the Saudi royal family happy, you can do it with your right foot; if you want to keep your family happy, you do it with your head.