Fuel is the No. 2 operating cost for trucking companies, just behind wages when measured by cost-per-mile. And fuel prices-already sky-high-are bound to jump further this winter, when heating oil competes for refiners’ time. So making a conscious operational decision to conserve fuel makes both dollars and sense.

When you set up your truck for top fuel economy, you’re really dealing with two key influences. The first-one you can’t so easily control-is the driver. Poor driving can negate any gains you’d hope to make through your spec. More on that later.

The second is your truck spec. An aerodynamic truck body, a productive and sensible gear ratio, maybe an on/off fan clutch, no bug deflector-smart choices really can make a difference. That on/off fan drive, for example, can offer measured savings ranging from 0.5% to 18%. Synthetic gear lubricant in axles and transmission can save up to 0.5% in summer and 2% in winter. Not bad. The trick is to remember that the percentage of gain for each device won’t accumulate arithmetically into a larger and larger total. The greatest numerical gains are enjoyed when a single device is applied to a truck that has nothing else going for it, fuel-economy-wise. If the truck is basically sound-mechanically and aerodynamically-each add-on results in less improvement. It has to do with physics and is a fact of life. So don’t go hog-wild in the trucker’s store.

When you get right down to it, some specs make more sense than others. Here are five:

1. AERO TRUCKS

Air resistance is a rig’s second greatest impediment to movement; only weight slows it down more. Good aerodynamics smooth the flow of air over, under, and around the rig; choosing an aero model can save up to 4 cents per mile in fuel, according to one truck manufacturer.

Aero-style trucks usually come with all the air deflectors included for your trucking application. If you pull a van or reefer, the most important deflector is the one on the cab’s roof. It moves air up and over the roof of the trailer. Without it, air blasts straight into the trailer’s nose, which is like pushing a barn door. It creates drag and requires plenty of fuel to overcome.

A full cab roof fairing-one that matches the height of the trailer-will save up to 15% compared to running with nothing at all. If your tractor has a raised-roof sleeper, chances are it’s a little shorter than the trailer’s roof, so you’d need a small fairing to kick the air completely up. Without it, you’d lose 4% to 10% of the benefits of a full roof fairing.

If you pull a low-height trailer, a full-height deflector would probably add resistance. You’d do better with a flat-roof or mid-roof sleeper that better matches your trailer. Because of this (and also to reduce purchase prices) aero tractors can be ordered with varying sleeper types (or with no sleeper at all). Work with your sales person to pick one that’s right for your operation.

Other deflectors usually come as a package on an aero tractor. These include cab extenders, which plug some of the gap between tractor and trailer; side skirts, which cover the fuel tanks and battery box and smooth out the profile of the steps; and an air-dam front bumper. Put any of these on a non-aero tractor and you might pick up 1% to 3% in fuel economy. So what? What if you run chromed-up, long-nosed “owner-operator” models to attract and retain good drivers, and you’re happy to pay the fuel “penalty”? You might offer to share fuel savings with them if they agree to drive an aero model instead. All other things being equal, lots of drivers would change jobs to get a 2- to 4-cent-a-mile raise.

2. ELECTRONIC ENGINES

At the same horsepower output, an engine with electronic controls burns 7% to 15% less fuel than one with mechanical controls. Electronics also help the engine make more power for its size and clean up combustion to meet exhaust emissions limits. That’s why nearly all new trucks come with electronically controlled engines.

Some guys stick with mechanicals because that’s all they know, or because fuel economy is less important (local trash and construction trucks are examples). But as mechanical engines become rare, the cost of producing their pumps, injectors, and other components goes up, negating any savings.

If you’re buying a used truck, you’ll be better off with an electronically controlled diesel. They’re reliable, use less fuel, make less smoke, and allow quick and easy diagnosing of problems (learn what “fault codes” displayed by a readout or light on the dash mean by looking in the owner’s manual). If you’re ordering a new truck, consider the high horsepower and torque available in electronically controlled engines with smaller displacements. You’ll save weight and money by buying an 11- or 12-litre diesel instead of a 14- or 15-litre model, and your trucks will still get down the road rapidly.

3. GEAR FAST, RUN SLOW

Gear ratios in the transmission and rear axle(s), along with the tire and wheel size, determine how fast the engine will spin at a given road speed. Each must be chosen with the other in mind. The best way to use gearing to save fuel is to “gear fast, run slow.” Set up the truck so it can run fairly fast, but instruct drivers to cruise slowly (or at moderate speeds) so the engine loafs. Most trucks are geared for 75 or 80 mph but cruise at 65 mph or so, where the engine will turn over at 1400 to 1600 rpm. This is the engine’s “sweet spot,” where it uses the least fuel; exactly where that spot is will vary with the engine make and model, so check out its specifications before picking or approving the gear specs.

If you want the truck to cruise at 75 mph, it can be done. Just be realistic when telling a salesperson how fast you usually cruise (do traffic and road conditions really let you go 75 mph most of the time?). If you run cross-country and that speed varies from 55 to 75 mph, pick a multispeed transmission that lets drivers split up or down to lower or raise engine speed.

Axle ratios are said to be “fast” or “slow.” All other specs being the same, the higher the axle’s numerical ratio (for instance, a 4.11), the slower the truck can run. The lower the number (like a 2.90), the faster the truck can run. You can pick either ratio type, or something in between. Just be sure the transmission’s top-gear ratio is something that works well with the axle. An overdrive top-gear ratio is usually paired with a slow (numerically high) axle ratio, and a direct-drive transmission is typically used with a fast (numerically low) axle.

4. TIRE SIZE & TYPE

A rig’s overall gearing changes with the diameter and circumference of its tires (expressed as “revs per mile”). So size matters. And size actually changes constantly because tread wear reduces diameter and circumference. You might lose 2 to 3 mph in cruising speed at a given engine rpm as tire treads on the drive axles reach their wear limit. The upside is the engine might feel gutsier, especially while accelerating or climbing hills, because the overall gearing is “slower.”

Tread type greatly affects fuel economy because it helps determine rolling resistance. For instance, a lug-type drive-axle tire in winter improves traction but adds resistance, and costs 2% to 4% in fuel economy. Installing “shallow rib” tires on the trailer can save 6% to 14% in fuel compared to regular ribs.

How about “low rolling resistance” tires? Manufacturers have put a lot of money into designing casings, treads, and rubber compounds that reduce friction and let the truck roll easier. Improvements can be measured in tests, and “coast-down” demonstrations can be convincing. However, traffic, terrain, and pavement conditions can negate gains to where they are minuscule or unmeasurable. If you run in flat country on good roads and can buy easy-rolling tires at a decent price, fine. Otherwise, consider other factors like total tread mileage, durability, and, of course, the added cost.

5. LAY THE EGG

Driving techniques make or break fuel economy. You can argue that time is money, so spending more for fuel can make sense if you can cover more ground in a day. But the faster the truck goes, the more fuel it’ll use. An old rule of thumb says it costs 0.1 mpg for every 1 mph over 55. Even with excellent aerodynamics, the truck will use 5% to 8% more fuel for every 5-mph increase in road speed.

Some conditions drivers can’t do much about. Winter operations consume 8% to 12% more fuel than summer running: rain, ice, snow, and cold temperatures all add to rolling resistance and stiffen gear lubricants, and the engine’s likely to idle more. Compared with open highways, steep hills might cost 4% to 18% in fuel, and stop-and-go traffic in towns and cities can cost 45% to 165% more.

But mostly, it comes down to throttle control. So we’ll leave you with a trick of the trade: tape a raw, Grade-A egg to the bottom of each guy’s right foot. He’ll go easy on the accelerator and the brakes-and greatly improve his mpg numbers.

Okay, the egg is a crazy idea. But asking your drivers to pretend it’s there might be a fuel-wise move.

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IDLING: COSTLY PROPOSITION

Most drivers need to idle their engines to heat the cab. But if they can cut engine idling time from 50% to 10%, you’ll save about 7% in mpg. Ask them to shut off the engine at rest stops (while using the facilities or phone, etc.), during meal breaks (the A/C or heater will quickly recool or reheat the cab as the truck gets underway), and even while waiting at long traffic lights. Better still, spec a darned good auxiliary cab heater and pay for it with what you’ll save on fuel.

FUELISH THOUGHTS

o Low restriction exhaust, including large-diameter pipes and dual exhausts, can save 0.3% to 2% over a cheap but restrictive exhaust system.

o Double trailers cost 6% to 10% more fuel to pull than a single semi because doubles have an extra gap (between the two trailers); a van with exterior posts costs 2% to 4% more in fuel than one with smooth sides; and a 13-foot, 6-inch-high van costs 2% to 8% more to pull than one that’s 12 feet 6 inches high (depending on tractor aerodynamics).

o Bug deflectors can cost as much as 1.5% in fuel because they “spoil” air flow over the hood (factory engineers cringe when they see a deflector on an aero tractor). So delete the deflector and break out the wash bucket.

o A broken-in truck suffers fewer parasitic losses due to the parts “settling in” and the brakes dragging less. After about 10,000 miles of break-in, a truck or tractor should use 2% to 5% less fuel than a new one.

Source: The Maintenance Coucil of the ATA