Driving Economically

Most truck drivers aren’t known for being tree huggers. When it comes to being fuel efficient – an area closer to the fleet manager’s heart than whether his drivers are doing their bit to save the rain forest – the typical fleet driver might dredge up some passion if the incentives are there in the paycheck. Left to their devices a lot of guys will probably opt to outrun their pals if they can, leaving any concern for mileage at the loading dock.

And why not? There may be more money in getting to the next load and the next more quickly than there is in chugging up hills looking for the sweet spot. Over the course of a year a guy might make more money pulling a few more loads than he will collecting fuel bonuses. There is always a reason to get where you’re going a little quicker. Why then do fleets even have fuel bonuses? They make more money if you pull more loads, too, right?

Maybe. On the other hand, it is possible a driver can be smart about fuel and get to those loads in good time, too. Fuel efficiency and productivity are not mutually exclusive. You can make money on top of the money you’re making by collecting fuel bonuses. For the owner-operator this is even more true. You could say it’s the difference between running hard and running smart.

Being fuel efficient and getting to those few extra loads on time is precisely the point of one time-honored if under-used driving technique: progressive shifting. You may have heard of it. At PGT, a flatbed carrier in Monaca, Pa., this technique has been turned from lip service to gospel. With the help of computer programs softwared into PGT’s driving simulator, drivers learn, or re-learn, the lesson that thinking about torque rather than horsepower when choosing shift points will provide higher miles per gallon while gaining acceleration to cruising speed.

The simulator program is based on the knowledge that Class 8 engines have changed dramatically in the last 10 years. Older engines were “peaky.” Their torque came on suddenly and dropped off just as suddenly. Since slight speed changes are what cause changes in torque, older engines gained and lost torque frequently, making it difficult to maintain good operating performance, defined by Charles Allen, director of sales and marketing for ZF Meritor, as “an engine operating at 90 percent of its rated power after a shift.”

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Mark Conover, Cummins’ automotive marketing strategist, owner-operator business, says, “Newer engines have flat torque curves.” A flatter torque curve means there is torque available in a broader rpm range and the curve does not peak then fall off suddenly, becoming less available at higher rpms. Torque bands now rest comfortably somewhere between 1,000 and 1,600 rpms, depending on the engine. Within that band torque is constant, falling off after reaching 1,500 or 1,600 rpms, once again depending on the engine.

According to Dave Dudo, safety director at PGT, the GE I-Sim simulator demonstrates to drivers that understanding torque is the key to understanding progressive shifting. “A lot of drivers still drive as if they had a 318. The old engines had to be wound up tight to run well. Not anymore. Running the rpms to 1,800 or higher with every shift is an out-of-date technique that costs money for fleets and owner-operators and does not get guys to speed nearly as quickly as they expect. They hear the engine whine and get the sensation they are accelerating more quickly than if they shifted sooner and stayed within the torque curve.”

As proof Dudo pointed out a comparison of two drivers. Each was driving the simulator program for a 3406E 435 Cat with a 10-speed loaded to 72,000 pounds. One used the old technique of shifting at the top of the rpm range in every gear. The second driver shifted at 1,400 and did not shift down until 1,000 rpm when climbing grades. Driver one, Bill Moody, a longtime owner-operator and current field safety inspector with PGT, used .77 gallons of fuel to reach 65 miles per hour. He required 2,992 feet and 64.6 seconds to get there. Driver two, Dave Dudo, used progressive shifting and used .58 gallons of fuel to reach the same speed. He got there in 2,256 feet and 61 seconds.

Flat torque curves have not changed the fact that there is a sweet spot at which the engine has reached its most efficient operating range and is using as little fuel as possible to maintain speed. This spot is 1,250 for the Cat 3406E in 10th. The sweet spot is the place to put it in cruise and allow the engine to lope as much as possible. Using cruise after getting to speed with progressive shifting is the thoroughly modern way to manage your drive train, save fuel and remain productive.

That flat torque curve has another advantage. It has made it less necessary to manage the drive train with closer-stepped trannies. Ten speeds now do the job that 13- and 18-speed transmissions used to do. Allen says it this way, “Contemporary engines have much wider operating ranges and almost constant horsepower throughout the operating range. Therefore for applications that may have needed the close-spaced steps of a 13- 15- or 18 speed transmission 10 to 15 years ago to ensure proper power and acceleration and to maximize fuel economy, a 10-speed transmission today may actually be perfectly suited.”

In an operational sense, the closer-stepped transmissions do have an advantage, according to Ed Saxman, director of power train systems for Volvo Power Train. The sophisticated driver can “dial them in,” as Saxman says. Rather than cruising in ninth at 55 to get through Ohio, for example, and have few rpms left at the top of the gear, or be in 10th and lug, a 13 or 18 can be split to dial in the desired rpms. Close-stepped transmissions are certainly also desirable when climbing. Then all those split gears need not be used all the time. As Conover says, “wider-stepped transmissions run in an efficient operating range, between 1,100 and 1,300 rpms. Drivers can let the direct shifts lug. The driver with the 13 or 18 can simply not split and achieve the same effect.” Instead of staying dialed in on hills, drivers with 10 speeds can use the modern flat-torqued engines to pull a little slower because there is less overall ratio coverage. However, using the entire rpm range, in particular the bottom end between 1,100 and 1,300 where the engine can now safely lug, saves fuel. Fleets spec wider steps for this cost savings.

Of course, speed is still the No. 1 culprit in lost fuel economy. “Every mile per hour over 50 requires another 10th of a gallon of fuel,” says Tom Liethen, a fuel economy expert for Kenworth. While few if any drivers are going to run 50 miles an hour, the same numbers hold for speeds over 65. Running the speed limit – rather than the five to 10 over many drivers assume is their birthright – will save you between half a gallon and a gallon of fuel per hour. Over the course of a year, this can amount to somewhere between 1,250 and 2,500 gallons based on a legal 10-hour day and 250 driving days.

Many fleets are also trying to cut fuel consumption by encouraging drivers to idle less. It takes about a gallon of fuel to idle for an hour, so that idling overnight may take 10 gallons and cost nearly $20. And while no one wants you to freeze or roast, there are instances you can cut idle time. Fleets like Crete Carrier and Schneider National are looking for idle averages of 25 percent. If you need your fuel bonus and your safety bonus to pay for Christmas, paying attention to idle times can boost your efficiency. Added to the fuel you save doing the speed limit, you can save another 2,500 gallons by never idling overnight.

Perhaps the most neglected aspect of fuel economy is tire maintenance. The Tire Information Retread Bureau estimates that 10 pounds per square inch under inflation will cost .5 percent in miles per gallon. This means that if you are getting 6 mpg with properly inflated tires, you will get 5.97 mpg with under-inflated tires. If you run 100,000 miles it will take an extra 84 gallons of fuel. TRIB recommends checking pressures every week using a digital air gauge. Tires should always be checked when they are cold. Thumping tires says absolutely nothing about tire pressure. The Technology and Maintenance Council says it takes 20 minutes to check and adjust inflation pressure. Those 20 minutes added to a pretrip once a week can save fuel, but they can also reduce the number of time-consuming tire problems. Under inflation causes heat buildup. Heat causes premature tire failure.

By saving money you are saving fuel and tires. It is enough to know you are taking home more bacon by exercising your true birthright – the right to drive smart rather than hard.

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