2019 Peterbilt 579: Towing Capacity & Payload

The 2019 Peterbilt 579 is a Class 8 semi-truck designed for hauling massive loads, with a Gross Combination Weight Rating (GCWR) of up to 80,000 pounds.

Quick Answer

Because the 2019 Peterbilt 579 is a Class 8 commercial semi-truck, its capabilities are measured differently than consumer-grade pickup trucks. Instead of a "towing capacity," these trucks are rated by Gross Vehicle Weight Rating (GVWR) and Gross Combination Weight Rating (GCWR). Towing capacity is determined by subtracting the truck's curb weight from the GCWR.

• Maximum Gross Combination Weight Rating (GCWR): Up to 80,000 lbs (standard), configurable higher with proper permitting.
• Gross Vehicle Weight Rating (GVWR): Varies by axle configuration, typically from 32,000 lbs (tandem axle) to over 52,000 lbs.
• Curb Weight: Highly variable based on configuration (sleeper size, engine, fuel tanks, etc.), but typically in the 15,000 to 19,000 lb range.
• Payload/Cargo Capacity: This refers to the weight of the trailer and its cargo. For an 80,000 lb GCWR and a 17,000 lb truck, the total trailer and cargo weight would be 63,000 lbs.
• Hitch: Commercial fifth-wheel hitch plate. Tongue weight is not a relevant metric; this is managed by the "kingpin weight," which is typically 15-25% of the trailer's total weight.

Tow Ratings by Engine & Drivetrain

Class 8 truck ratings depend on the specified axle ratings, engine, transmission, and intended application. All configurations are designed to handle the 80,000 lb standard GCWR when properly equipped. The primary difference between powertrains is performance—how efficiently and quickly the truck can move the load.

Note: Final capacity is always determined by the manufacturer's specifications on the door jamb sticker and federal/state regulations.

Towing Features

The 579 is a dedicated towing machine and comes standard with all necessary heavy-duty equipment. There isn't a separate "tow package" as you'd find on a light-duty truck.

• Transmission Cooler: All automated manual and automatic transmissions on a Class 8 truck are equipped with heavy-duty cooling systems.
• Integrated Brake Controller: Air brake systems are standard. The truck's service brakes are controlled by a foot pedal, and the trailer brakes are controlled via a hand-operated lever (trolley brake) in the cab. These systems are fully integrated.
• Engine Braking: The PACCAR MX and Cummins X15 engines feature powerful integrated engine brakes (Jake Brakes) which are critical for controlling speed on downgrades with heavy loads.
• Trailer Connections: Connections are made via a pigtail for air lines (service and emergency) and a 7-pin electrical connector for lights.

5th-Wheel & Gooseneck Capability

The Peterbilt 579 is exclusively designed for use with a commercial fifth-wheel hitch. The frame is not designed for and should never be used with a gooseneck ball. The fifth-wheel plate is mounted directly to the truck's frame and is designed to handle the immense vertical load (kingpin weight) and articulation forces of a commercial semi-trailer.

Weight Distribution & Safety

Weight distribution is critical in commercial trucking. Proper loading of the trailer is essential to ensure that the steer axle and drive axles remain within their legal weight limits. Weight is managed by placement of the cargo within the trailer and by adjusting the position of the sliding fifth-wheel hitch and the trailer's axles (if slidable).

SAE J2807 is a standard for light and medium-duty trucks and is not applicable to Class 8 vehicles like the Peterbilt 579. The performance and testing standards for these vehicles are governed by the Federal Motor Carrier Safety Administration (FMCSA).

Real-World Towing Tips for This Vehicle

• Know Your Weight: Always scale the truck and trailer at a certified CAT scale after loading to ensure you are compliant with axle weight and gross weight limits.
• Use the Engine Brake: Rely on the engine brake to control your speed on downgrades, saving your service brakes for when you need to stop.
• Plan Your Route: Be aware of bridge laws, weight-restricted roads, and steep grades.
• Conduct Thorough Pre-Trip Inspections: Check your tires, brakes, lights, and coupling connection every single time before you roll.

Common Towing-Related Issues

While the 579 is a robust platform, common issues are related to the high-stress nature of heavy hauling.

• Air System Leaks: Constant use can lead to leaks in air lines or fittings for the brakes and suspension, which can be a serious safety violation.
• Brake Wear: Despite the use of engine brakes, service brakes on the truck and trailer are wear items and require regular inspection and replacement.
• Driveline Stress: U-joints and carrier bearings are under immense torque. Regular lubrication and inspection are key to preventing on-road failures.
• Aftertreatment System Faults: Modern diesel emissions systems (DEF/DPF/SCR) can be complex and are a common source of maintenance issues that can de-rate engine power if not addressed.

Whether you're dealing with routine maintenance or a complex driveline issue, it’s important to have a qualified technician. Find a trusted shop on Repairius.