2018 Kenworth T680 Towing Capacity & Payload Guide

The 2018 Kenworth T680 can tow anywhere from 60,000 to over 100,000 pounds, depending on the specific engine, axle configuration, and permitted Gross Combined Weight Rating (GCWR). Because the T680 is a Class 8 commercial heavy-duty truck (a "semi" or tractor-trailer), its towing capacity is dictated by federal and state bridge laws, axle ratings, and the heavy-haul specifications ordered from the factory, rather than standard consumer truck metrics.

Always remember that for commercial vehicles, the exact ratings can vary dramatically based on the spec sheet. You must verify the door-jamb sticker and VIN plate for your specific truck's legal limits.

Quick answer

• Max Tow Capacity: 60,000 to 100,000+ lbs (dependent on trailer weight, heavy-haul spec, and state permits).
• Max Payload (Tractor + Trailer): 45,000 to 80,000+ lbs (varies entirely by trailer type and empty weight).
• GVWR: 35,000 to 60,000+ lbs (depending on 4x2, 6x2, or 6x4 axle configuration).
• GCWR: 80,000 lbs (standard legal limit); up to 140,000+ lbs (heavy-haul configurations).
• Curb Weight (Tractor Only): Approximately 15,000 to 18,000 lbs (depending on sleeper cab size and fuel tanks).
• Hitch Class: Commercial 5th-wheel plate (standard consumer hitch classes and tongue weights do not apply).

Tow ratings by engine & trim

Since the T680 is a custom-built commercial vehicle, there are no traditional "trims." Instead, capacities are based on the engine, drivetrain (axles), and frame thickness. Below is a general guide to typical GCWR limits based on engine choice. Keep in mind that "Max Tow" is calculated by subtracting the tractor's curb weight (approx. 17,000 lbs) from the GCWR.

Note: Consumer light-duty pickup trucks are rated using the SAE J2807 standard. SAE J2807 ratings do not apply to Class 8 commercial semi-trucks like the Kenworth T680.

Tow package contents

When ordering a heavy-haul or maximum towing configuration for a 2018 Kenworth T680, the upgrades differ significantly from a passenger vehicle. A commercial "tow package" typically includes:

• Heavy-Duty Cooling System: Upgraded radiators and cooling fans to handle sustained high-rpm pulls up mountain grades.
• Transmission Cooler: High-capacity coolers for automated manual transmissions (like the PACCAR 12-speed or Eaton Endurant) or Allison automatics.
• Engine Braking: Multi-stage compression release engine brakes (Jake Brakes) to manage heavy loads on steep descents without overheating the service brakes.
• Upgraded Axles & Suspension: Heavy-duty front steer axles (up to 14,600 lbs) and tandem rear drive axles (up to 46,000 lbs) with heavy-duty air-ride suspension.
• Air Brake Connections: Standard red and blue gladhands for trailer air brakes, plus a 7-way commercial electrical connector (different from a consumer 7-pin).

5th-wheel & gooseneck

Because this is a Class 8 semi-truck, it utilizes a commercial-grade 5th-wheel hitch rather than a standard pickup truck gooseneck or RV 5th-wheel.

• Commercial 5th-Wheel: The T680 is equipped with a cast steel 5th-wheel top plate (often manufactured by Holland, Fontaine, or Jost).
• Air-Slide 5th Wheel: Most models feature an air-actuated sliding 5th wheel, allowing the driver to move the attachment point forward or backward. This is critical for properly distributing the trailer's pin weight between the steer and drive axles to comply with DOT weigh station regulations.

Weight distribution & WDH requirements

Standard weight distribution hitches (WDH) are for consumer receiver hitches and are entirely irrelevant to the Kenworth T680.

Instead of a WDH, weight distribution in a Class 8 truck is achieved via sliding tandem axles on the trailer and the sliding 5th wheel on the tractor. Drivers must scale their loads to ensure they do not exceed legal per-axle limits: typically 12,000 lbs on the steer axle, 34,000 lbs on the drive axles, and 34,000 lbs on the trailer tandem axles (for a standard 80,000 lb legal load).

Real-world towing tips for this vehicle

• Manage Your Momentum: Even with a 600-horsepower Cummins X15, pulling 80,000 pounds requires anticipation. Maintain steady speeds and use momentum to climb hills.
• Use the Engine Brake Wisely: Save your foundation air brakes for coming to a complete stop. Use the engine brake to maintain safe speeds on long downgrades.
• Scale Every Load: Always hit a CAT Scale after picking up a heavy load. Adjust your sliding 5th wheel and trailer tandems to ensure your axle weights are legal before crossing state lines.
• Monitor Engine Temps: Heavy hauling, especially in the summer, will test your cooling system. Keep an eye on coolant and oil temperatures during long pulls.

Common towing-related issues

• Emissions System Faults (DPF/DEF): Extended idling or improper duty cycles can cause soot buildup in the Diesel Particulate Filter, leading to derate conditions when you need power the most.
• Air Leakage: Gladhand seals wear out frequently. Always carry spare rubber seals to prevent trailer air brake leaks.
• Automated Transmission Hunting: On steep grades with heavy loads, automated manual transmissions may sometimes "hunt" for the right gear. Switching to manual mode can lock the gear in and maintain pulling power.

If your rig is experiencing transmission issues, air leaks, or DPF faults, don't risk a breakdown under load. Find a trusted shop on Repairius.