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International ProStar ES -the most fuel-efficient truck on the market

It’s official: International has been hard at work designing, testing and tweaking an Efficiency Spec of its acclaimed ProStar® model, and it’s now on the market.

“Every customer is interested in making a dollar or saving one,” says Aaron Peterson, head of Performance Engineering, heavy duty platform. “And we wanted to see exactly how much efficiency we could squeeze out of this ProStar.”

Capable of over 9 mpg with an improvement in fuel economy of up to 11% compared with the previous generation, ProStar ES delivers.

Because fuel is often a freight company’s No. 1 cost of operation, the race toward efficiency now drives the entire competitive landscape. Peterson, who has 18 years of experience as an engineer doing everything from drawing parts to launching products, helped assemble a team of expert designers who dived headlong into optimizing the truck’s aerodynamics, drivetrain and onboard diagnostics system

The result? “We have the highest-quality truck on the road, no doubt about it,” Peterson says. “This product is capable of setting records. We’re delivering some of the best fuel efficiency many fleets have ever seen.”

Engineered by Experts
A few years ago, Peterson headed up something new for Navistar: the Performance Engineering Team. Working on the theory that listening to consumers is the key to delivering an elite product, International took its best engineers and put them in a room with their customers.

The team, made up of 15 specialists, is structured in two unique halves. One is the engineering arm, which works to develop designs and select technology. The other arm is platform-focused, which gives engineers the opportunity to interact frequently and directly with customers. “Most times engineers are isolated,” Peterson says. “They don’t get to see their product in the field.” For Navistar, this was a commitment to hear and implement customer desires.

Peterson flies around the country several times a week, meeting with buyers. “The biggest kick I get is working with customers who haven’t been educated on our new technology,” he says. “When you’re talking about fuel economy improvements in the range of 3%, 4%, even 5%, that’s a lot of money to customers every year. Getting to see the look on their faces when those first fuel bills start showing up: That’s what keeps me moving.”


In testing, engineers found that the ProStar could reach those gains while operating within a range of 62 to 65 mph. That kind of attentive research, combined with the team’s improvements through aerodynamic, drivetrain and software developments, resulted in a sum that transcended its parts.

“This is the truck where we put it all together,” says Caetano Calviti, chief engineer, Fuel Economy, Performance and Aerodynamics. “We don’t stop at good enough.”

Advanced Aerodynamics
The ProStar ES boasts industry-leading aerodynamics. “At Navistar, we take very seriously not only our simulations but also what happens in the real world,” Calviti says. That means designing for what’s known as wind average drag, which takes into account not just head-on air resistance but crosswinds as well.

Such a factor actually goes beyond the EPA’s regulations, which require only straight-ahead testing. “We take pride in looking at the full yaw curve of the vehicle,” says Patrick Yerkes, the team leader for Product Development. “By rotating at an angle around the vehicle, we can take a full measure of all the points where the wind is approaching and optimize for those conditions.”

The ES’s aerodynamic gains begin the moment the truck sticks its nose into the wind. The curved windshield, with its swept A-pillars, shoots the air up and around the body. Lower valance panels direct wind around and under the cab. Square edges are a real drag, so the cab and fenders feature smooth, parabolic shapes to help direct airflow both when it’s coming head-on and when the vehicle is hit with gusts from the side.

“Aerodynamics on a tractor-trailer is all about energy management from the very beginning of the cab to the very end of the trailer,” explains aerodynamics engineer Greg Harding. “We design and test primarily with scale wind tunnel and computational fluid dynamics models. We study pressure contours and streamlines. If we see any streamlines that are being disrupted, we’ll work to smooth them out.”

Optimized Drivetrain
Beneath the hood, the ProStar ES boasts advanced friction reduction, air management systems and control strategy developments that regulate the amount of torque being delivered. With this spec, engineers paid specific attention to downspeeding, the systematic process of decreasing the engine’s revolutions per minute.

For the past several years, International has shaved off about 25 rpm annually across its engine portfolio; but the ProStar ES represents a major leap, promising to shed 200 rpm. This reduces the parasitic losses that occur within the engine itself, and it spreads those gains throughout the vehicle to devices like water pumps, fans and even the alternator. “All of those are spinning slower,” Peterson says. “When they spin slower, they take less power. I’m comfortable in saying that this technology offers at least a 3% improvement over a conventionally geared vehicle.”

The ProStar’s axles are improved, as well. By offering a Meritor FUELite setup in a 6×2 configuration, the team has seen gains of 1.5% to 2%. “The less power you’re losing through the axles, the more power delivered to the road,” Yerkes says.

Software, too, plays a role. “Say you’re on cruise control, and you come up to a small hill. The ES has controls optimally tuning the power available to the task at hand,” Yerkes explains. “It allows us to gain fractions of fuel economy every time they crest a hill like that.”

Those fractions—a tenth here, a sixth there—are the products of millions of simulations, cycles and iterations the team has run in hopes of discovering where best to optimize. It’s this attention to detail that has resulted in the win. “The low-hanging fruit is gone,” Yerkes says. “You’re looking for a nickel here, a dime there. It’s the race that doesn’t end.” And Navistar engineers have sharp, fraction-catching eyes.

OnCommand™ Connection
Now that Navistar has delivered a hardware setup with the potential to break fuel economy records, what about the software that supports it? Meet OnCommand™ Connection, a data system designed to provide predictive diagnostics once the truck has left the lot.

Remotely accessible, it allows fleet managers to monitor the drivetrain and engine to make sure they’re working together at their full potential. The system is also programmed to send alerts for everything from component failure to routine maintenance. “At the end of the day, we make a huge effort to improve overall uptime,” Calviti says. “And OnCommand™ is a part of that.”

Perhaps that reveals something about International’s real goal with the Efficiency Spec: All of this research, precision and fat trimming has resulted in a truck that doesn’t just improve the efficiency of its fuel consumption; it improves the efficiency of the entire freight transportation process.


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