Paccar’s Kenworth and Peterbilt brands launched new medium-duty truck models in April for the Class 5 to Class 8 weight groups, which start in the 7,258-kilogram GVWR range and go up from there. Peterbilt is a relative newcomer to the medium-duty segment, only producing its first truck for that market in 1995, but it has been rapidly gaining market share there since then. For Kenworth, this marks the first update to its offerings in that weight group since 2007.
Peterbilt’s medium-duty Class 5 and 6 trucks are now the 535 and 536 models. Over at sister brand Kenworth, they’re the T180 and T280. Moving up in the weight classes, KW’s Class 7 T380 and Class 8 T480 are matched by Pete’s 537 and 548.
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Likely the first change buyers will notice is the much wider cabs. These two brands are infamous for their narrow cab designs, which go back decades and were initially intended as a way to make the trucks more aerodynamic. The downside is they reduce available interior space pretty significantly. The updated aluminum cabs on the new models now stretch to a width of 2.1 metres, making them eight inches (20 centimetres) wider than the previous generation. That provides enough room for three occupants.
Cab access is better now too, with a cab height that’s three inches lower, stair-style steps and knurled grab handles. The all-new doors feature larger windows for increased driver visibility. The company claims the new cab interior has a “best-in-class” fit and finish with high- or low-back seats in cloth or vinyl, along with lots of storage space. And the most important thing if you’re going to have three occupants — three cup holders.
The dash layouts have changed too, with a digital display screen and available space for optional gauges, switches and smartphone or tablet RAM mounts.
Debuting along with the new models was a new transmission, which gets bolted up to either of the Paccar PX-7 or PX-9 diesel engines. It’s an all-new automatic eight speed, dubbed the Paccar TX-8, which will be standard equipment on the medium-duty lines. The nine- and 12-speed automatics the brands have been offering will now be known as the TX-9 and TX-12.
For smoother shifting, the TX-8 uses twin torsional dampers. It also has first gear lockup, which is a feature that locks the torque converter at low speeds to improve fuel efficiency and drivability. The transmission also has a hill start aid to help prevent unintended vehicle roll back or roll forward.
A Multi-Skip Shift function provides quick and direct downshifts from any gear with immediate acceleration and speed control. The transmission’s Adaptive Start Gear optimizes the launch gear selection to reduce shifts while improving fuel economy, and the Neutral Idle Control will automatically shift into neutral when the brakes are applied. It also includes the ability to shift from automatic to manual mode.
The company says the TX-8 offers a 15 per cent improvement in acceleration and better fuel economy than other comparable transmissions.
According to Laura Bloch, Kenworth’s assistant general manager for sales and marketing, more than 90 per cent of Kenworth medium-duty trucks are ordered with an automatic transmission. “In addition to the performance and smooth shifting the Paccar TX-8 provides, it’s also leading the way in fuel economy. Depending upon the application, it can improve fuel economy by up to five per cent. It senses the road grade, vehicle acceleration, torque demand, weight and engine load to keep the truck in the most fuel-efficient gear possible,” she said.
The TX-8 transmission has been engineered for reduced maintenance, requiring an oil change only every 150,000 miles (241,000 kilometres). And it has a lifetime oil filter, which never needs changing.
For model year 2021, Paccar PX-7 engines are rated up to 325 horsepower and the PX-9 engine provides up to 380 ponies. Coinciding with the introduction of the new medium-duty lines, Kenworth will offer — for the first time in its medium-duty trucks — the 320-horsepower near-zero emission Cummins Westport L9N natural gas engine.
