Peterbilt 579 updated: Midrange trucks get wider cab

April 23, 2021

Tom Berg


Peterbilt 579 updated
The restyled Model 579 tractor looms big and black next to a new wide-cab 536 Class 6 truck painted Legendary Red. Both vehicles have lower noses for minimal wind resistance and good forward visibility. (Photo by Tom Berg)

The model number’s the same, but the Peterbilt 579 highway tractor has smoother aerodynamics for increased fuel economy and a redesigned interior that includes a large “digital dash” with color displays that mimic analog gauges, while interfacing with advanced driver-assist safety systems.

Meanwhile, the builder’s medium-duty conventionals are getting a wider cab to increase room for drivers and helpers and a new, efficient automated transmission for many engine ratings.

“The new 579 is the most technologically advanced truck Peterbilt has ever built,” declared Jake White, director of product planning, at a ride-and-drive event this week at the Texas Motor Speedway north of Fort Worth. It is also the most aerodynamic and fuel-efficient Peterbilt, he said, thanks to a new sloped hood and optimized aero components. Fuel economy is up to 7% better than the current 579 when equipped with Paccar MX diesels and automated transmissions.

Improved comfort comes from a 10% quieter cab and sleeper, additional storage, a new smart steering wheel with numerous built-in controls, and an improved Bluetooth microphone, White said. The 15-inch digital dash display delivers road, engine and safety-related information in a clean, colorful and intuitive interface, executives said.

Dash of the updated Peterbilt 579
Colorful digital dash display mimics analog gauges and can show a wide variety of engine and road condition numbers and indications. It’ll be standard on Models 579 and 567 this summer. Peterbilt’s display is somewhat simpler than the wing-adorned design offered by Kenworth. (Photo courtesy Peterbilt Motors Co.)


Driver assistance systems

Advanced driver assistance systems in the Peterbilt 579 include collision mitigation, lane departure warning, and the new lane-keeping assist, among others. Lane-keeping assist uses an electric motor on the steering column to boost effort in keeping a truck centered in its lane, thus reducing fatigue and tedium for the driver. Within the digital display are indicators and warnings for lane-keeping assist, frontal collision mitigation, and overspeed alerts.

A digital vision system provides drivers enhanced, camera-enabled vision around the truck at all times including at night and during inclement weather.

First major changes in decades

Peterbilt’s midrange conventionals have been marketed since the mid-1990s, and “95% of them are still in service, some in their fourth life cycles,” said Phil Hall, director of the builder’s development center and segment manager for medium-duty products. Enhanced aerodynamics, the wider cab and redesigned interior comprise the first major changes in all that time.

The restyled and redesigned models cover Class 5 through Baby 8, and are numbered 535, 536, 537 and 548. They will replace the 300 series that will phase out later this year. The 500 series’ most notable feature is a 2.1-meter-wide cab borrowed from certain heavy-duty Peterbilts and shared with Kenworth, a corporate sister, which showed off its new midrange models a few weeks earlier. The cab is 8 inches wider than that on the outgoing models.

“The 1.9-meter cab wasn’t wide enough,” Hall said, citing research done with customers’ drivers who explained their varying duties that involved frequently climbing in and out of cabs and motoring through urban and suburban locales. “So we rethought it” in the course of five years of development of the medium-duty replacements. Additional room in the wider cabs allows three-person seating with an optional two-place bench seat and more storage. A new instrument cluster, strong composite dashboards and easy-to-reach switches and controls should also make the new trucks more desirable to buyers.

Peterbilts distinct from Kenworths

Both medium-duty conventional lines are assembled at a Paccar plant in St. Therese, Quebec, outside of Montreal, and might be presumed to be all but identical except for nameplates. Not so, Hall insisted, for Peterbilt retained certain product details in the design process during which specialists from both builders collaborated. Instruments are illuminated in amber, which is easier on drivers’ eyes than the blue used on the rival sister’s gauge cluster.

The Petes also have doors with near-level window sills instead of the drop-down sills that are KW trademarks.

Mirror mounts on Petes and KWs are on the cowl, ahead of the doors, where vibration is low so sight pictures in mirror glass are steady, and the mounts will break away but not shatter in a minor collision. A 250-pound showoff can do pullups on a mirror mount, Hall said, but he didn’t demonstrate. The grille includes three vertical bars that are carefully shaped to reflect light so the truck is identifiable as a Peterbilt as it approaches. Not so with an optional flat-black grille aimed at “work truck” buyers who disdain chrome and the lavish spending it might suggest.

Taking the Peterbilt 579 for a spin

Like Kenworth, Peterbilt is using a new ZF-made eight-speed automated transmission and Paccar-branded diesels sourced from Cummins. Engines are the 6.7-liter PX-7, with ratings of 230 and 260 horsepower, and the 8.9-liter PX-9, with ratings up to 360 horsepower.

Drives were limited to an infield portion of the speedway, which is surrounded by a long, fast NASCAR-spec oval track. The fastest this reporter got a truck was an indicated 41 mph during a pedal-down acceleration run that was interrupted by a sharp right-hand curve. This was with a Class 6 Model 336, one of several I sampled, powered by a Cummins-supplied Paccar PX-7 diesel and a ZF-built TX-8 automated transmission. The stakeside flatbed was empty, so the engine was especially gutsy, and the self-shifting transmission operated appropriately and unobtrusively. Allison midrange automatics are also available, and standard on heavier medium-duty Petes.

A brief spin in the Peterbilt 579 tractor running bobtail offered limited impressions, but one strong sense was that it was like driving a nimble living room on wheels. The comfort and quietness were that good. This tractor had a long sleeper and an MX-13 diesel, assembled by Paccar in Columbus, Miss., with a 12-speed automated transmission, made by Eaton and called the Paccar Endurant. This was a smooth combination, but Peterbilt also offers the smaller-displacement Paccar MX-11 and the larger Cummins X15, along with Eaton automated and manual gearboxes.

Also shown at the event was an updated Model 567, Peterbilt’s principal vocational model that, along with the current Peterbilt 579, have used the wide cab since the mid-teens. The 567’s current popularity with construction fleets should be boosted with refinements including the new colorful digital dash. It will become standard on 567s and 579s this summer. LL

Phil Hall, midrange segment manager and former design chief, explains the strong cowl mount that provides a steady base for the rear-view mirror
Phil Hall, midrange segment manager and former design chief, explains the strong cowl mount that provides a steady base for the rear-view mirror. Note the near-level window sill on door, a Peterbilt feature unlike the cut-down sills on Kenworth models. Vocational versions have extra-stout frames for the rigors of on/off-road travel. (Photo by Tom Berg)


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Tom Berg worked his way through college by driving trucks. Since 1978, he’s been writing about trucks and trucking. He holds a Class A commercial driver’s license and drives trucks as part of story research. While semi-retired, Berg still writes about semis as a contributing editor at Land Line.