Towing a trailer is not the nerve-wracking experience many people imagine, but proper equipment is necessary. Is your vehicle powerful enough to pull your trailer? Is your vehicle properly equipped for towing?

Your vehicle was primarily designed to carry passengers and cargo. It is important to remember that towing a trailer will place additional loads on your vehicle's engine, drivetrain, steering, braking and other systems. However, if you decide to tow a trailer, using the prior equipment is a must.

Local laws may require specific equipment such as trailer brakes or fender mounted mirrors. Check your local laws.

Trailer weight

The weight of the trailer is the most important factor. A good weight-to-horse-power ratio is about 35:1-35 pounds (16kg) of gross cargo weight (GCW) for every horsepower your engine develops. Multiply the engines rated horsepower by 35 and subtract the weight of the vehicle, passengers and luggage. The result is the approximate ideal maximum weight you should tow, although a numerically higher axle ratio can help compensate for heavier weight.

It is always a good idea to check your owner's manual for specific towing recommendations from the manufacturer. This will avoid overloading your vehicle and prevent potential damage to the drivetrain.

Hitch (tongue) weight
See Figures 1 and 2

Calculate the hitch weight in order to select a proper hitch. The weight of the hitch is usually 9-11% of the trailer gross weight and should be measured with the trailer loaded. Hitches fall into various categories: those that mount on the frame and rear bumper, the bolt-on or the weld-on type used for larger trailers. Axle mounted or clamp-on bumper hitches should never be used.

Installation of a bolt-on hitch is easy. When the hitch is installed, the tongue should be level and parallel to the road, and in the exact center of the vehicle.

Check the gross weight rating of your trailer. Tongue weight is usually figured as 10% of gross trailer weight. Therefore, a trailer with a maximum gross weight of 2000 lbs. (908 kg) will have a maximum tongue weight of 200 lbs. (90 kg)-Class I trailers fall into this category. Class II trailers are those with a gross weight rating of 2000-3000 lbs.(908-1362 kg), while Class III trailers fall into the 3500-6000 lbs. (1,590-2,724 kg) category. Class IV trailers are those over 6000 lbs. (2,724 kg) and are for use with fifth wheel trucks, only.

If you're installing a load-distributing hitch, the vehicle will "squat" front and rear when the trailer is coupled. You will have to get the hitch ball at the height where the vehicle will be when fully loaded. Add the average "squat" to the distance from the ground to the top of the coupler to get the ball height.

To determine the average "squat," multiply the hitch weight by two-thirds. Load this weight into the front seat (use approximate weight of people) and measure how much the vehicle squats from the unloaded height both front and rear. Average the front and rear figures.

Load distributing hitches generally use equalizer bars and chain links to level the tow vehicle after the trailer is hooked up.

With the trailer directly behind the vehicle, measure the vehicle height front and rear. Hook up the trailer and adjust the chain links so that it levels the vehicle and provides approximately the same vehicle height, front and rear, with maybe ½ inch (13mm) difference.

For larger trailers or if you are towing with a short vehicle, a sway control may be necessary. The sway control connects between the hitch and the tongue of the trailer. It dampens the swaying motion of the trailer and helps keep the trailer under control. While testing the rig, you should be able to let go of the wheel and feel no fishtailing.

Wiring the vehicle for towing is fairly easy. There are a number of good wiring kits available and these should be used, rather than trying to design your own.

All trailers will need brake lights and turn signals as well as tail lights and side marker lights. Most areas require extra marker lights for over-wide trailers. Also, most areas have recently required back-up lights for trailers, and most trailer manufacturers have been building trailers with back-up lights for several years.

Additionally, some Class I, most Class II and just about all Class III trailers will have electric brakes. Add to this number an accessories wire, to operate trailer internal equipment or to charge the trailer's battery, and you can have as many as seven wires in the harness.

Determine the equipment on your trailer and buy the wiring kit necessary. The kit will contain all the wires needed, plus a plug adapter set which includes the female plug, mounted on the bumper or hitch, and the male plug, wired into, or plugged into the trailer harness.

Several popular kits are on the market that don't require cutting into your factory wires at all. Instead, they tee into a junction point in the rear of the vehicle. When installing the kit, follow the manufacturer's instructions. The color coding of the wires is usually standard throughout the industry.

If you own vehicle with separate turn signals, the wiring problem is slightly more complicated. Some domestic vehicles, and most imported vehicles, have separate turn signals.

The most practical way around this is to use a commercially available isolation unit, which takes separate brake and turn signal impulses and combines them into a common output to the trailer, allowing use of the standard harness.

Otherwise, the wiring is the same as for conventional vehicles, except that you tap into the isolation unit.

One final point-the best kits are those with a spring loaded cover on the vehicle mounted socket. This cover prevents dirt and moisture from corroding the terminals. Never let the vehicle socket hang loosely; always mount it securely to the bumper or hitch.

You should also use a variable load or heavy-duty flasher to take care of heavier demands on your turn signals.

Most trailer wiring connectors follow an SAE standard for wire color and position. However, there are some exceptions. When wiring a trailer use the standard to avoid potential electrical damage and to make hooking up to different trailers easier.

Trailer brakes
See Figure 8

Two types of trailer brake systems are currently in use -- hydraulic (surge) brakes and electric brakes.

Hydraulic braking is performed by the installation of a controller and master cylinder mounted on the tongue of the trailer. The system operates much like the drum brakes on your vehicle. The push of the trailer on the tow vehicle during deceleration synchronizes the trailer brakes with the tow vehicle braking action. As the trailer pushes against the tow vehicle during a stop, the actuator pushes a piston in the master cylinder and supplies hydraulic pressure to the wheel cylinder. The wheel cylinder expands the brake pads against the drums and slows the trailer.

Electric brakes are a popular option on trailers because of their reliability and simplicity of operation. Most states require electric brakes to be installed on trailers of a certain weight rating, or on trailers which have multiple axles.

The electric brake system is actuated by a controller mounted under the dashboard. As the tow vehicle's brakes are applied, a signal from the brake light switch is sent to activate the controller. Simultaneously, the pendulum weight inside the controller moves forward, changing the resistance inside the controller and activating the trailer brake magnets. The natural G-force of deceleration move the pendulum in direct proportion to the amount of braking applied by the driver.

Back at the wheels, an electromagnet pivots on an arm with a cam that is attached between the brake shoes. When the magnet is energized, it attempts to follow the rotation of the brake drum. This causes the cam to rotate, actuating the primary brake shoe. The movement of the primary shoe causes the secondary shoe to activate, thus stopping the trailer.

If you own or plan on towing a trailer with electric brakes ensure your vehicle is properly equipped with the appropriate electric brake controller.

Engine

A frequent hazard of towing is engine overheating, due to increased load. To aid cooling, most manufacturers include a heavy-duty cooling system as part of the trailer package. It usually consists of a larger capacity radiator, heavy-duty water pump and coolant recovery system. A/C equipped vehicles also use a clutch-type fan, which uses a heat sensor, allowing the fan to free-wheel, or push air, depending on engine temperature.

Cooling System

One of the most common, if not THE most common, problems associated with trailer towing is engine overheating. Cleaning and flushing the cooling system is good preventive maintenance. Ensure all cooling system components are functioning properly. If your vehicle is not equipped with a factory towing package, installation of aftermarket high capacity radiators, high flow water pumps and auxiliary electric cooling fans will all help keeping your vehicle running cool.

Oil Cooler

Aftermarket engine oil coolers are helpful for prolonging engine oil life and reducing overall engine temperatures. Both of these factors increase engine life. While not absolutely necessary in towing a Class I trailer, all vehicles towing Class II trailers and above should be equipped with an engine oil cooler. Engine oil cooler systems usually consist of an adapter, screwed on in place of the oil filter, a remote filter mounting and a multi-tube, finned heat exchanger, which is mounted in front of the radiator or air conditioning condenser.

Transmission/transaxle
See Figures 9 and 10

In recent years, the automatic has become the recommended transmission for trailer towing. The overall reliability and power of the automatic makes pulling easier than having to ride the clutch and lug the rig to get moving.

On the negative side, the automatic transmission is far more complicated than a manual, and overheating is responsible for the majority of automatic transmission failures. Under normal service, fluid is designed to last about 50,000 miles (80,450 km) at operating temperatures of 195°F (90°C). As the temperature of the fluid increases, the life of the fluid decreases rapidly-a 20°F (-7°C) temperature rise will halve the life of the fluid:

• At 212°F (100°C), fluid life is 25,000 miles (40,200 km)
• At 235°F (113°C), fluid life is 12,500 miles (20,100 km)
• At 255°F (124°C), fluid life is 6,250 miles (10,000 km)
• At 275°F (135°C), fluid life is 3,000 miles (4,800 km)

Installation of an oil cooler will protect against high heat and premature transmission failure. A 20° drop in transmission fluid temperature will approximately double the fluid life; most coolers will reduce temperatures by 30° or more.

A transaxle cooler can, sometimes, cause slow or harsh shifting in the cold weather, until the fluid has a chance to come up to normal operating temperature. Some coolers can be purchased with or retrofitted with a temperature bypass valve which will allow fluid flow through the cooler only when the fluid has reached above a certain operating temperature.

To select a cooler:

1. Estimate the combined weight of the vehicle and the load pulled or carried.
2. Select a cooler of equal capacity.
3. Determine the mounting location. Be sure that cooling is adequate and that the cooler will fit.
4. If you are planning a by-pass installation, select a cooler two sizes larger.

Continue to page 2 of Trailer towing

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