Can a tow truck fix a flat tire?

The calculation people skip

GVWR and GCWR are defined at 49 CFR § 571.3. Towing capacity is GCWR minus the fully loaded tow vehicle — not a standalone number off a brochure. Passengers, fuel, cargo and the hitch itself all come off before anything is attached.

Tongue weight, and why it bites twice

Tongue weight runs 10–15% of loaded trailer weight for a conventional bumper-pull, and 15–25% for a fifth-wheel or gooseneck. Tongue weight counts against payload, not only against the tow rating.

Where the published number comes from

Modern published tow ratings come from SAE J2807, which specifies a Davis Dam grade test and defined acceleration and braking criteria. The full standard is paywalled: we cite the standard and a manufacturer's J2807 explainer, and we never invent figures from it.

Because ratings vary by trim, axle ratio, cab configuration and model year, we do not publish per-model capacity figures. The calculator linked below works from the numbers on your own vehicle instead, which is the only version of this answer that is reliable.

The sticker that overrides every website

The door-jamb label carries your vehicle's actual GVWR and its payload for the configuration it left the factory in — the number that a brochure figure, and this page, cannot know. Payload is the one people blow through first, because tongue weight lands on it alongside passengers, fuel and cargo. A half-ton pickup can be comfortably under its tow rating and simultaneously over its payload with four adults aboard and a loaded trailer on the ball.

The weakest link is rarely the engine

Pulling weight is easy; stopping it is not. Most states require trailer brakes above a threshold weight, and the hitch, ball mount and ball each carry their own rating that can sit below the vehicle's. The effective capacity of the whole arrangement is the lowest of those numbers, not the highest, and a class-III receiver fitted with a lower-rated ball mount is limited by the ball mount. Check every component's stamp, not just the truck's specification.

What quietly reduces the number

Published ratings assume conditions your trip may not match. Altitude reduces available power, sustained grades load the cooling system, and headwinds and roof cargo add drag that the rating never contemplated. Aftermarket changes matter too: larger tyres and a lift alter effective gearing and raise the centre of gravity. None of this appears in a capacity figure, which is why experienced towing leaves margin rather than running to the published maximum.

Common mistakes

• Using the brochure maximum as your capacity — it assumes a base trim, no cargo and one occupant.
• Forgetting tongue weight counts against payload — you can be under the tow rating and over the payload at once.