Before You Tow

1. The numbers, and where each one lives

Towing is governed by about seven figures, and the confusing part is that they are kept in four different places. Three are stamped on your vehicle, two are only in the owner's manual, and two depend on how you load on the day. Here is the whole set.

2. Reading the two labels in your door jamb

Open the driver's door and look at the jamb and the door edge. Federal rules require two labels there, and between them they answer about half the questions above. Knowing what is not on them saves the most time of all.

The Safety Compliance label

Required under 49 CFR Part 567. A white or silver label, usually on the jamb itself. It carries the manufacturer's name, the month and year the vehicle was built, the VIN, the GVWR, and the GAWR front and rear — each with the tire, rim and cold inflation pressure those axle ratings assume.

The Tire and Loading Information label

Required under Federal Motor Vehicle Safety Standard 110. Usually on the door edge or the jamb beside the first one, and often yellow-and-white. It gives the seating capacity, the original tire sizes and their cold pressures, and — the useful part — a sentence reading "The combined weight of occupants and cargo should never exceed X lbs." That figure is your payload, and it is specific to the vehicle as it left the factory.

If you have no manual, every major manufacturer publishes an annual towing guide as a free PDF, indexed by year, model, engine, cab and axle ratio. Search for your make, the model year and "towing guide". Match all of the columns, not just the model name.

3. Payload is usually the real limit

Most people who run out of truck run out of payload, not tow rating — and they never find out, because payload is the one limit nobody thinks to check. It is also the only check on this page you can complete today, unaided, with a sticker you already have.

Here is the mechanism. Tongue weight does not travel with the trailer; it presses down on your hitch, which means it is weight you have added to the vehicle. It comes out of the same payload allowance as your passengers, the cooler, the tools in the bed and the weight-distribution bars themselves.

So the arithmetic goes like this. Say the label in your jamb reads 1,600 lb, and you are travelling with three other adults and some gear:

At 13% — a fair middle figure for a ball coupler — 900 lb of tongue weight corresponds to a loaded trailer of about 6,900 lb. That is your payload ceiling. It is very often thousands of pounds below the tow rating printed in the same truck's brochure, and it is the number that actually binds.

Two things that quietly eat payload, worth knowing before you are surprised by them: a weight-distributing hitch head and bars are typically 60 to 100 lb of it, and any accessory fitted after the vehicle left the factory — a bed cover, a rack, running boards, heavier tires — comes off the top, because the label was printed before they existed.

Under-loading the tongue is the other failure. A trailer loaded tail-heavy will start to sway above about 50 mph and the sway gets worse the harder you correct it. Load the heavy items forward of the trailer's axles, and keep the tongue inside the band in chapter 1.

4. Hitches, couplers, brakes and plugs

Four separate compatibility questions, and all four have to be yes before a trailer can leave. We check them with you at pick-up, but they are much easier to sort out at home than in the yard with a booking waiting.

Receiver Classes

Receiver hitches are sold in classes. Each class implies a receiver-tube opening and a weight band. The figures below are the typical ones:

From Class III up, many hitches carry two sets of numbers: a lower "weight carrying" rating and a higher "weight distributing" one. The higher figure only applies with a weight-distribution system actually fitted — the spring bars that transfer some of the tongue load forward onto the front axle. If you are near the top of a hitch's range, that is not optional equipment.

Couplers and Balls

The ball has to match the coupler stamp exactly. This is the one that causes accidents: a 2 inch coupler will drop onto a 1-7/8 inch ball, latch, and look completely normal — then release over the first sharp bump. Read the size stamped on the coupler and fit that ball, not the one already on the mount.

• 1-7/8 inch — small utility trailers, commonly rated to around 2,000 lb.
• 2 inch — the most common size by a distance. Rated anywhere from 3,500 to 8,000 lb depending on the ball and shank, so the diameter alone tells you nothing about the rating.
• 2-5/16 inch — heavier trailers, commonly 6,000 lb and well up from there.
• Gooseneck ball — mounted in the truck bed over the rear axle rather than behind the bumper. For the heaviest trailers, and it needs a bed hitch already installed.
• Pintle ring — a hook-and-ring coupling rather than a ball, common on equipment trailers. Needs a pintle hook on the vehicle; a ball mount will not do.

Every ball has its own working load stamped on the top face. That stamp is the rating — not the diameter, and not whatever the hitch behind it is rated to.

Brakes

What the trailer has decides what your vehicle needs:

• Electric brakes do nothing at all without a brake controller in the cab. No controller, no brakes — the trailer will roll up behind you under braking as though it had none, because it has none.
• Electric over hydraulic also needs a controller, plus the trailer's own pump. Stronger, and just as dependent on what is in your cab.
• Surge or hydraulic brakes are self-actuating: the coupler compresses under deceleration and applies them. Nothing needed in the cab, which makes them the easy case — though backing up a slope wants a reverse lockout, and that is a wire.

Many states require working brakes on any trailer above a certain weight, and the threshold is set state by state. If you are towing across a state line, the rule that applies is the one where you are driving.

Light Connectors

• 4-pin flat — tail, brake and turn signals only. No brake circuit at all.
• 5-pin flat — the four above plus one more, usually a reverse lockout for surge brakes.
• 6-pin round — older standard; lights plus a brake circuit.
• 7-pin round, the RV blade — lights, electric brakes, a 12 V charge line and reverse. What most heavier trailers expect.

5. When a CDL actually applies

This is the most misquoted rule in towing, and it is misquoted in the direction that costs people a trailer they were entitled to rent. The weights that circulate are right. The condition attached to them usually gets dropped.

The federal rule is 49 CFR Part 383. A Group A commercial driver's license is required when all three of the following are true:

1. The vehicle is used in commerce — in trade, traffic or transportation, or in something affecting it. In plain terms: for business.
2. The gross combination weight rating — or the actual combined weight, whichever is greater — is 26,001 lb or more.
3. The towed unit's GVWR, or its actual weight, whichever is greater, is more than 10,000 lb.

Work an example. A 10,200 lb trailer behind a 17,000 lb truck is 27,200 lb combined, and the trailer is over 10,000 lb. A contractor hauling equipment to a job site in that combination needs a Class A. The identical trailer, behind the identical truck, moving a homeowner's own dirt around their own property, is not being used in commerce — and the federal rule does not reach it.

Note "whichever is greater" in both conditions. It appears twice, and it means actual weight counts as well as the ratings. You cannot get under the rule by pointing at a modestly-rated setup while running heavier than it says.