How it works
In plain English, three separate limits all have to be respected, and the smallest one wins. First, the GCWR method: take the Gross Combined Weight Rating, subtract the tow vehicle's curb weight and the weight of passengers and cargo in it — what is left is the most trailer weight the combined rig can carry. Second, the payload method: take the tow vehicle's GVWR, subtract its curb weight and the passengers and cargo in it — that is the payload available. Because tongue weight presses down on the tow vehicle, divide that payload available by the tongue percentage to get the largest trailer whose tongue weight fits the payload. Third, the manufacturer's tow rating is a hard cap on its own. The limiting factor is simply the smallest of the tow rating, the GCWR method result, and the payload method result.
Example: GCWR 18,500 − curb 4,700 − passengers/cargo 500 = 13,300 lb by the GCWR method. Payload available is GVWR 7,050 − curb 4,700 − passengers/cargo 500 = 1,850 lb, and 1,850 ÷ 12% = 15,416.67 lb by the payload method. Against a tow rating of 13,000 lb, the smallest number — the tow rating — is the limit.
Frequently asked questions
Why is the answer the smallest of the three?
Each limit guards something different — the combined rig, the tow vehicle's own load, and the manufacturer's tow rating. Passing one limit does not excuse breaking another.
Where do I find GCWR, GVWR, and curb weight?
On the door-sticker label and in the owner's manual for your exact vehicle and configuration. Do not use a brochure maximum for a different trim or axle ratio.
What if my tongue percentage is different?
Change the tongue % box. A higher tongue percentage means the same payload supports a smaller trailer, so the payload method result falls.