How Trailer Towing Safety Works

Trailer hitch
You can connect vehicles together using devices like this towing hitch. See more car safety pictures.
Dan Driedger/iStockphoto

Sometimes, towing a trailer is really handy. For example, if you're moving to a new house, you may want to hook up a trailer to your vehicle rather than hire someone else to move your belongings. But even if your vehicle is rated and equipped to tow, you shouldn't just head out on the highway. While trailers are useful, they can also be hazardous. If you don't follow proper safety procedures, you could put yourself and your property at risk.

Before we get too involved, it will help to learn a little about the equipment you'll encounter when towing a trailer. There are three common types of trailer hitching systems:


  • Weight-carrying hitches
  • Weight-distributing hitches
  • Fifth-wheel hitches

We'll concentrate on the first two hitching systems. They use a trailer hitch receiver mounted on the back of the towing vehicle. The fifth-wheel hitch is different -- instead of attaching to the back of a vehicle, it hitches to a special connector in the bed of a pickup truck. The connector is just in front of the rear axle.

Towing a camper
Here's an example of a fifth-wheel trailer hitch.
Sebastian Iovannitti/iStockphoto

For weight-carrying and weight-distributing hitches, you'll encounter a lot of the same hardware. On the tow vehicle side, you have the trailer hitch receiver, which attaches directly to the tow vehicle. Next, you'll need a draw bar or ball mount. These attach to the trailer hitch receiver -- you use a locking pin to secure the mount to the hitch. On top of the ball mount is, naturally enough, a ball. The size of the ball will determine the type of trailer you'll be able to hitch to your vehicle.

On the trailer side, you have the trailer itself. The section of the trailer that extends out to connect to the tow vehicle is the tongue. On the end of the tongue is a coupler. The ball from the tow vehicle fits into the coupler. A weight-distributing hitch has special equipment designed to spread the weight pressing down on the tongue to the axles of both the tow vehicle and the trailer. Weight-carrying hitches put the full tongue weight on the tow vehicle. We'll look into that further in the next section.


Most trailers have their own light and brake systems. In all cases, you'll have to connect these systems to your own vehicle before they'll work. To power the light system, newer tow vehicles usually have a connector stowed in a convenient location. With an older vehicle, you may have to connect the trailer's electrical system through your taillights.

Let's take a closer look at the steps you should follow when you connect your trailer to your tow vehicle.



Connecting a Trailer for Towing

Towing a trailer
Even in light traffic, avoid speeding while towing a trailer.
Tim McCaig/iStockphoto

Before you hook up a trailer to a tow vehicle, you need to take the following into consideration:

  • How much weight can the tow vehicle pull safely? This information should be in your owner's manual.
  • How much weight can your trailer hitch and ball mount handle (tongue weight)? You can adjust tongue weight either by using a weight-distributing trailer hitch or by balancing the load inside the trailer itself.
  • How much weight can the trailer carry safely? Manufacturers set weight ratings for trailers. Exceeding this limit is unwise -- you could risk equipment failure.
  • How much will the trailer weigh when loaded? This is called the gross trailer weight (GTW). The maximum weight of the trailer and tow vehicle combined is the gross combination weight rating (GCWR). Again, it's unwise to exceed this manufacturer-recommended weight limit. You can weigh your vehicle and trailer on a public scale.
  • Is the load inside the trailer balanced properly? Are the items inside the trailer secure? Unbalanced loads can cause problems like trailer sway on the road.
  • What are the local and national laws you'll need to follow? Some areas have strict laws regarding trailer size and weight. Make sure you research these laws before you leave home.

With that out of the way, let's look at the process for connecting a trailer. The coupler on the tongue of the trailer should fit over the ball on the trailer hitch ball mount. Make sure the equipment matches up -- if the trailer's coupler doesn't match up to the ball on the ball mount, you can't tow with that trailer safely. The coupler should have a securing device that you'll need to lock into place. This prevents the coupler from detaching from the ball mount.


You should then attach safety chains to the trailer tongue and your trailer hitch. The chains should cross underneath the tongue of the trailer. That way, should the trailer break away from the hitch, the chains will be able to support the tongue. Make sure you leave some slack in the chains -- tight chains will inhibit your ability to make turns.

Some trailers -- in particular larger trailers that can haul more than 1,500 pounds (680 kilograms) -- have braking systems. There are two major kinds of brake systems for trailers: surge brakes and electronically-controlled brakes. Surge brakes are hydraulic brakes that have an activation switch located in the trailer tongue. Should the trailer tongue break away from the trailer hitch, the switch activates the brake system. Electronically-controlled brakes connect to the tow vehicle's electric system. The driver can activate electronically-controlled trailer brakes using a hand control located within easy reach of the driver's side -- usually on the console itself.

Many trailers have electric systems. Trailers use connectors to plug into a tow vehicle's electric system. New basic trailers might have a simple four-way connector. Each connector controls a different function. A four-way connector could supply power and control to taillights, brake lights, turn signals and side marker lights. Some newer trailers and tow vehicles can take advantage of seven-way connectors, which may also provide power to a trailer power supply, braking system and backup lights. If the connector on your trailer doesn't match up to your vehicle, you can use an adapter to solve the problem.

Once you've connected your trailer to your tow vehicle and checked to make sure everything is safe and secure, it's time to hit the road.


Trailer Towing Driving Safety

Going camping
Remember to maintain your equipment and be safe on the road.
Jill Fromer/iStockphoto

If you take nothing else away from this article, please remember this: Practice is critical. If you're new to towing, you'll need to get some practice under your belt before hitting the road. Your vehicle will respond differently when towing a trailer than it will on its own. Even a simple task like coming to a stop takes practice. If at all possible, practice towing a trailer in a large area like an unoccupied parking lot.

If you're towing a trailer that has a wider wheel base than your tow vehicle, you may need to replace your normal side view mirrors with a larger set or use mirror extenders. These will give you a better view around the sides and even allow you to see behind the trailer. In the United States, several states require you to use extenders if you're pulling a trailer over a certain size.


A wider trailer also means you have to be careful when making turns. The trailer's wheels will be closer to the edges of the curve. If you're not mindful of the difference, you risk hitting a curb or other object, which could cause damage to your trailer's wheels and axle. So remember to allow extra room when you're turning while towing.

You should always be particularly careful when you are accelerating and braking while towing. Remember that by towing a trailer, your vehicle has much more mass than normal. This mass has momentum and inertia. Inertia is the tendency for an object to maintain its current state of momentum -- or motion -- without interference from an exterior force. An object with more mass will also have greater momentum and inertia. That means your tow vehicle will have to work harder when pulling a trailer -- the added mass requires more energy to move and stop.

Because your vehicle has to work harder to accelerate and brake, it's a good idea not to drive too fast. Speeding will put more wear and tear on your vehicle. Your engine will have to work harder and it could also put a strain on its suspension, brakes and other systems. Also, you'll need more room to slow down or come to a stop. You shouldn't follow other vehicles too closely -- you won't have time to stop if something goes wrong.

Another reason not to speed is because it can cause trailer sway. Trailer sway is a very dangerous situation. Together, a tow vehicle and trailer create an articulated vehicle. That means one section of this overall vehicle (the point where the coupler and trailer hitch meet) is flexible to an extent. If it weren't, you'd have a hard time making turns. But being articulated also means that the rear of the vehicle can move somewhat independently of the front. That's the basis of trailer sway.

A trailer may begin to sway back and forth if the load inside it isn't balanced properly, if a gust of wind hits it or during acceleration (particularly if the vehicle is traveling downhill). At first, the sway may be minor. But under certain conditions, the sway could get worse -- the trailer begins to move back and forth, gaining momentum on each swing. Unchecked, the trailer could cause you to jackknife. Or it might cause you to lose control of the tow vehicle and have an accident.

Trailer sway can be terrifying and difficult to correct. The best way to solve the problem is to apply the trailer's brakes (but not the tow vehicle's brakes) and come to a gradual stop. Don't try to steer out of it -- you'll just magnify the situation. Once off the road, try balancing the trailer load. If that doesn't solve the problem, stop driving and call for help -- trailer sway has led to several accidents, some of them fatal.

With the right approach and equipment, you should be able to tow a trailer safely to your destination. Remember that the important thing is to practice and keep a level head. And have a good trip!


To learn more about towing, take a look at the links on the next page.


Lots More Information

Related HowStuffWorks Articles

More Great Links


  • Allen, Mike. "Saturday Mechanic: Wiring Your Trailer Hitch." PopularMechanics. Feb. 2004. (Sept. 24, 2008)
  • AON Recreation. "What You Need to Know to Tow." 2007. (Sept. 22, 2008)
  • Camping-Canada. "Towing Tips." 2008. (Sept. 22, 2008)
  • Cook, Miles. "Trailer Towing Q&A." Edmunds. (Sept. 23, 2008)
  • eTrailer. "Tips on How to Tow a Trailer." (Sept. 22, 2008)
  • Green Defensive Driving Course. "Tips for Towing a Trailer." 2007. (Sept. 23, 2008)
  • Henderson, Tom. "Newton's Laws of Motion." The Physics Classroom Tutorial. 2007. (Sept. 22, 2008)
  • Henderson, Tom. "The Impulse-Momentum Change Theorem." The Physics Classroom Tutorial. 2007. (Sept. 22, 2008)
  • Hokin, Sam. "The Physics of Everyday Stuff." (Sept. 22, 2008)
  • Physics Classroom Tutorial. "Newton's Laws of Motion." 2007. (Sept. 22, 2008)
  • Tools of the Trade. "Towing Safety." Tools of the Trade Magazine. Nov. 1, 2006. (Sept. 23, 2008)
  • United States Department of Transportation. "Safety Tips for Driving with a Trailer." (Sept. 23, 2008)
  • State of California. "Towing Your Trailer Safely." 2007. (Sept. 24, 2008)
  • National Highway Traffic Safety Administration. "Towing a Trailer." April 2002. (Sept. 24, 2008)