2020 Peterbilt 579 Towing Capacity & Payload

This guide details the towing capacity and payload specifications for the 2020 Peterbilt 579. The 2020 Peterbilt 579 is not designed for conventional trailer towing, but rather for heavy-duty trucking applications as a semi-trailer tractor. Its towing capabilities are determined by its Gross Combination Weight Rating (GCWR) and the weight of the semi-trailer it is designed to pull, typically with a fifth-wheel coupling. You will generally not find a conventional "hitch class" or "tongue weight" for this type of vehicle. Its primary function is to haul large commercial trailers.

Quick answer

• Max Towing Capacity: Up to 80,000 lbs (GCWR dependent, and not a conventional tow rating)
• Max Payload: Geared towards semi-trailer kingpin weight capacity rather than a distinct "payload" like light-duty trucks.
• GVWR: Varies significantly based on axle configuration, typically 35,000 lbs to 60,000 lbs or more.
• GCWR: Up to 80,000 lbs (standard), higher for specialized heavy-haul applications.
• Curb Weight: Approximately 17,000 - 20,000 lbs (tractor unit only, varies by configuration)
• Hitch Class: Fifth-wheel coupling and/or Pintle hook (not rated by conventional hitch classes 1-5)

Tow ratings by engine & trim

The Peterbilt 579's "tow rating" is fundamentally different from that of light-duty trucks. It's defined by its Gross Combination Weight Rating (GCWR), which is the maximum permissible combined weight of the tractor and a fully loaded trailer. The engine and drivetrain configuration directly impact the GCWR and the vehicle's ability to haul heavy loads.

Note: The "Max Tow" in a conventional sense is not applicable. The GCWR represents the total maximum weight the vehicle can legally move, including its own weight, the trailer's weight, and the cargo.

Tow package contents

For heavy-duty semi-trucks like the Peterbilt 579, a "tow package" isn't a bundled option in the same way it is for light-duty pickups. Instead, the entire vehicle is configured for towing (hauling semi-trailers). Key components often include:

• Heavy-Duty Cooling System: Essential for maintaining optimal engine and transmission temperatures under constant heavy load.
• Integrated Trailer Brake Controller: Standard for managing the air brakes of semi-trailers.
• Trailer Sway Control: While not an explicit "control" system like in light-duty trucks, the inherent stability of a fifth-wheel connection and multi-axle trailers inherently mitigates sway.
• 7-Pin and other electrical connectors: A robust electrical system is in place to power trailer lights, ABS, and other auxiliary functions on the semi-trailer.
• Air Suspension and Axle Configurations: Optimized for load distribution and ride quality with heavy trailers.

5th-wheel & gooseneck

The 2020 Peterbilt 579 is exclusively designed for 5th-wheel semi-trailer applications. It does not typically utilize gooseneck hitches, which are more common for heavy-duty pickup trucks. The fifth-wheel coupling is integrated into the chassis, allowing for superior load distribution and stability when pulling large commercial trailers. The kingpin weight capacity is dependent on the axle ratings and suspension setup of the specific truck.

Weight distribution & WDH requirements

Weight distribution hitches (WDH) are not used with fifth-wheel setups on semi-trucks. The fifth-wheel coupling inherently distributes the trailer's kingpin weight directly over the truck's drive axles, providing excellent stability and load transfer. The design of the Peterbilt 579 handles significant vertical loads at the fifth-wheel. Proper load securement within the semi-trailer is crucial for maintaining safe axle weights.

Real-world towing tips for this vehicle

Operating a 2020 Peterbilt 579 with a semi-trailer requires specialized knowledge and training. Here are some critical tips:

• Pre-Trip Inspection: Conduct thorough pre-trip inspections of both the tractor and trailer, including tires, brakes, lights, and coupling mechanism.
• Load Distribution: Ensure the trailer is loaded correctly to prevent exceeding axle weight limits and to maintain stability. Imbalanced loads can lead to handling issues.
• Braking Distance: Remember that braking distances are significantly longer with a loaded semi-trailer. Anticipate stops and maintain ample following distance.
• Gear Selection: Utilize the appropriate gear for the terrain to manage engine RPMs, maintain speed, and control descents using engine brakes.
• Mirror Usage: Constantly monitor mirrors to be aware of your trailer's position and surrounding traffic.
• Weather Conditions: Adjust driving style for adverse weather. High winds, rain, or snow can dramatically impact handling and braking.

Common towing-related issues

While the Peterbilt 579 is built for heavy hauling, certain issues can arise:

• Brake System Malfunctions: Issues with air lines, air tanks, or brake adjustment can compromise stopping power.
• Tire Blowouts: Overloaded or improperly inflated tires are a common cause of blowouts, especially on trailers.
• Kingpin/Fifth-Wheel Wear: Regular inspection of the fifth-wheel mechanism is crucial to prevent wear that could lead to disengagement.
• Electrical Problems: Trailer light failures or ABS warnings often stem from faulty wiring or connectors.
• Cooling System Overheating: Pushing the truck beyond its GCWR or operating in extreme conditions can lead to engine or transmission overheating.

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