The most valuable rule of thumb for towing is to coordinate the weight capacities of the equipment so the entire rig is stable, allowing for a ride that's not significantly different than if the vehicle were towing nothing at all. This arrangement gives drivers the advantage of a predictable response to traffic maneuvers, so all they have to think about is a smooth, even ride. Experienced drivers have all seen trailers that threatened to pass the tow vehicle or wiggle like hyper-happy puppies, or tow vehicles riding painfully high in the front and awkwardly low in the rear. These are examples of mismatched pieces: too much or too little tongue weight, too heavy a trailer weight for the vehicle, and so forth.
The first step before hitching up a trailer to your vehicle is to spoon through a bowl of alphabet soup of terms for towing. Knowing how to decipher these acronyms for capacities and weights and how they relate to one another takes the guesswork out of towing and helps the driver progress to master-tower.
GVWR (Gross Vehicle Weight Rating): The total allowable weight of a fully loaded vehicle, including driver, passengers, cargo, fluids, accessories and tongue weight. Beefy aftermarket shocks or airbags won't change the vehicle's GVWR, they just make the ride more comfortable. One of the biggest mistakes amateur towers make is to underestimate the total weight within the tow vehicle.
GAWR (Gross Axle Weight Rating): The maximum weight a single axle is designed to safely carry. This rating is provided to prevent single-axle overloading.
Tow Rating: The manufacturer's recommended towing capacity often based, for larger trucks, on the GVWR plus 2,000 pounds, engine size and axle ratio.
GTWR (Gross Trailer Weight Rating): This figure is located on a metal tag on the trailer frame and is based on the allowable weight of the trailer and its cargo.
GCWR (Gross Combined Weight Rating): Total weight of the tow vehicle and everything in it, as well as the trailer and its contents. If the truck weighs out at 7,000 pounds and has a GCWR of 10,000 pounds, the trailer and its contents cannot exceed 3,000 pounds.
Once you have made sense of these terms as they apply to your situation, you're in a good position to determine if a vehicle is safe to tow the intended trailer and its contents. One rule of thumb: it's far better to have too much tow vehicle in terms of weight and towing capacities than too little. The maneuver that has saved many a road trip is to power the trailer out of trouble—whether it's a heavy crosswind or a fishtailing trailer coming down a grade at highway speeds. The ability of the tow vehicle to regain control, to actually continue to tow instead of being pushed, is vital to everyone's safety. A good example is a two-horse trailer pulled by a 1/2-ton pick-up. Technically, the 1/2-ton is adequate and many recreational, short-distance horse-towers trailer successfully with this set-up. But those who have spent many long hours transporting livestock wouldn't be caught dead in a 1/2-ton. Experience has taught these veterans that a 3/4-ton is the safest tow vehicle for a horse trailer.