The best fuel economy starts with a truck model specifically designed to squeeze the most possible miles from a gallon of diesel fuel, and all major builders offer these for their on-highway customers. Some have snappy names, others don’t, but all have these elements in common:
Advanced aerodynamics resulting from thousands of hours in computer-simulation and wind-tunnel testing, to reduce air drag at highway speeds;
Down-sped engines, which cruise at 150 to 200 rpm less than normal, reducing internal friction;
Automated manual transmissions, which work with engines and shift themselves through carefully calibrated settings in their electronic controls, allowing the worst driver to perform almost as well as the best; and
Low-rolling-resistance tires, to further reduce mechanical drag on the rig.
For best results, trailers should also have low-rolling-resistance tires, and vans and reefers should have aero improvers. Such equipment is required in California for vans and reefers 53 feet or longer. Here we concentrate on the tractors:
Freightliner Evolution I
The Evolution I (for innovation) package combines the Cascadia Evolution’s advanced aerodynamics with the integrated Detroit Powertrain. Adding EPA SmartWay-verified tires gains SmartWay certification for the tractor. The i Package is available as a 125-inch BBC daycab, and with Mid Roof and Raised Roof sleeper options.
It includes chassis fairings that extend and flare out at the end of 12- or 20-inch side extenders; contoured bumper with an air dam and gap fillers; thin-film radio antennas placed under the cab’s roof structure; drive axle wheel covers; and a front axle air deflector. Powertrain includes Detroit Diesel DD15i rated at 400 hp and 1,750 lb-ft, with a downsped, low-rpm cruising speed and usable torque generation as low as 975 rpm. Intelligent Powertrain Management uses GPS to pinpoint the vehicle’s location and looks ahead to anticipate terrain, then adjusts cruise control, pre-selects gears in the DT12 automated transmission, and uses eCoast and engine retarding to maximize operating efficiency.
A 6x4 tandem can be had with a “fast” 2.41 ratio and a 6x2 tandem is available with the 2.41 or an even faster 2.28 ratio. “Over the last 24 months, 67% of all Cascadia 72-inch Raised Roofs built were Cascadia Evolutions,” says Mary Aufdemberg, Freightliner’s director of product marketing.
International ProStar ES
The ProStar ES combines advanced aerodynamics with a Cummins ISX15 or a Navistar N13 diesel mated to an Eaton Advantage Automated transmission, whose controls are calibrated to work closely with either engine. Both are downspeed-capable, allowing the engine to cruise 150-300 rpm slower at cruising speed than previous offerings. Navistar engineers did full-scale wind tunnel testing to validate the performance of the package in crosswind situations, which on average account for a larger portion of aero resistance than direct headwinds. They found up to 11% better fuel economy with the ES package than previous models.
The ES package also includes a choice of Dana Advantek 40 or Meritor’s 14X high-efficiency 6x4 drive axles, or Meritor’s FuelLite 6x2 drive axle, all riding on SmartWay certified tires in duals or wide-base singles. Navistar’s Performance Engineering Team can further refine specs for individual applications, and an ES comes with a three-year subscription to OnCommand Connection, Navistar’s predictive diagnostic system that monitors vehicle performance in real time. ES is approved for up to 80,000 pounds GCW, and an ES 110 is good for up to 110,000 pounds GCW.
“Around 20% of our ProStar volume is for this fuel-efficient package,” says Jodi Presswood, VP and general manager for heavy duty trucks.
Kenworth T680 Advantage
The T680 Advantage’s optimized powertrain consists of the latest Paccar MX-13 diesel with the Eaton Fuller Advantage 10-speed automated transmission, fuel-efficient drive axles, and a special aerodynamic package. This includes longer 76-inch sleeper side extenders, lower cab fairing extenders, front air dam, aerodynamic mud flaps, and rear fairing without steps, coupled with an air deflector, exhaust cut out covers, and optional wheel covers for drive tires.
Other fuel-saving components available include wide-base single tires, tire pressure monitoring, Idle Management, Driver Performance Assistant, and Driver Reward software. Coming mid-year is a predictive cruise control with neutral coast mode that will anticipate the terrain ahead and ensure that the engine and transmission are operating in the most efficient mode for it. The T680 Advantage claims a fuel economy gain of 10% over earlier models with the previous generation MX diesel.
“Customer acceptance of the T680 Advantage was high in 2014, and we expect excellent growth for the T680 Advantage this year,” says Kurt Swihart, Kenworth marketing director.
The Pinnacle axle-back model combines advanced aerodynamics with Mack’s integrated powertrain. It’s available in several configurations, including an EPA SmartWay-certified version. Roof and side fairings can be optimized for a specific van or reefer types, and side shield, chassis fairing extenders and ground effects packages are available. Lightweight Advantage main frames can be further lightened with aluminum crossmembers. Mack’s 10.8-liter MP7 and 12.8-liter MP8 diesels are standard with the mDrive 12-speed automated manual transmission.
A Super Econodyne option downspeeds engines at cruise and employs Mack proprietary axles. An optional Load Logic system reads data from a sensor in the rear suspension to determine whether or not a load is present, and tells the transmission to cruise in 11th-direct or 12th-overdrive. An available 6x2 tandem with a liftable pusher axle automatically raises or lowers that axle for less drag or to help shoulder heavier loads.
“Because the Pinnacle model can be spec’d for such a wide variety of applications, it’s tough to give a specific percentage on who’s choosing those options,” says Stu Roselli, Mack’s on-highway segment marketing manager. “It’s safe to say that a majority of Pinnacle model orders include some combination of fuel-saving options.”
Peterbilt 579 Epiq
Peterbilt’s newest Model 579 Epiq integrates advanced aerodynamics, an optimized powertrain with the Paccar MX-13 diesel and other fuel-saving technologies to achieve up to 14% better fuel economy. Four different Epiq aero packages can meet a full range of business and application requirements. Fairings include 18-inch sleeper side extenders with 8-inch rubber flares; rubber skirting along the chassis fairing from the quarter fender to the front of the tandem, with rubber closeouts under the sides of the cab and sleeper; and roof fairings with a rear wall closeout. Aero-enhanced components include a three-piece bumper; multi-piece hood; painted outside sun visor; and an aero-style aluminum battery box on the driver side, under the cab.
An Apex powertrain pairs the Paccar MX-13 diesel with a Fuller Advantage Automated transmission communicating via proprietary control logic for precise control. Other features are low-rolling-resistance tires and a Bendix SmarTire pressure monitoring system, plus Driver Performance Assistant and predictive cruise control.
“The Model 579 Epiq has been well received by customers, from large fleets to smaller ones,” says Anthony Gansle, marketing manager, on-highway product. “The Model 579 makes up a significant volume of our production and the Model 579 Epiq represents a healthy portion of that.”
Volvo VNL 670
The 2016 Volvo VNL 670 features a recently refined aerodynamic package, offering fuel savings of up to 3.5% vs. a 2015 model. Among the enhancements are a re-contoured bumper and lower airflow deflector; a roof air deflector that better complements the aerodynamic roof fairing and adjustable trim tab; and flared chassis fairings that move air past the drive wheels and tractor-trailer gap. A new “smart” fan clutch runs the fan only when extra cooling is necessary, and varies fan speed based on need.
The VNL 670 features a 61-inch tall sleeper and is available with Volvo’s D11, D13 or D16, or Cummins’ ISX15 diesels. Ratings go from 355 hp to 600 hp, and torque ranges from 1,250 lb.-ft. to 2,050 lb.-ft. Volvo’s I-Shift automated manual transmission is standard on all Volvo-powered truck models. Also available are XE (eXceptional Efficiency) powertrain packages, which allow the engine to cruise at about 200 rpm less than a typical truck sold today. XE specs include Volvo power, the Volvo I-Shift operating in overdrive, “fast” rear axle ratios and low-profile tires. “Volvo VNL 670 is our best-selling model ever,” says spokesman Avery Vise.
Western Star 5700XE
The recently introduced 5700XE features razor-edged styling that efficiently cuts through air and makes the new model the most aerodynamic of Western Star’s offerings. An optimized aerodynamics package is available for day cab, 68- and 82-inch configurations, and includes an aero roof cap, 20-inch cab side extenders, and chassis side fairings. The 5700XE uses a 126-inch-BBC cab with five sleeper options from 34 to 82 inches in length with Low and High roofs, and on the 82-inch sleeper, an available Ultra-High roof. Available powertrains use Detroit DD13, DD15 and DD16 diesels, preferably with the Detroit DT12 automated manual transmission. Eaton 9-, 10-, 13-, 15- and 18-speed manuals are also available. All 5700XEs come standard with Detroit’s Virtual Technician diagnostic system.
“To date, more than 90% of Western Star customers have selected the full aero treatment of chassis side fairings, roof cap and cab side extenders,” says Ann Demitruk, director of marketing. “Over a third of the customers are choosing the integrated Detroit Powertrain package to further optimize efficiency. The IDP package is available in both a 6x2 and 6x4 configurations.”