By Matthew Barnes
Hauling heavy loads or towing a heavy trailer are complicated tasks; in fact, they are more complicated than they look. Key to safe towing or hauling is knowing your vehicle's weight limitations and having your vehicle properly equipped.
Heavy loads or a heavy trailer can make the back of your vehicle sag, and that can seriously impact safety by shifting your vehicle's center of gravity and making it more difficult to control. To compensate for sagging, many automakers and aftermarket parts manufacturers offer load-leveling systems.
These systems raise the rear of the vehicle back up to its unloaded height. Besides balancing the vehicle's load, this also helps level out the headlights so that you aren't blinding other drivers at night. Driving with an unlevel load also can cause other problems such as uneven tire wear, higher fuel consumption and greater strain on the axle.
We're going to look at two of the most common ways to level a load — airbags and self-leveling shock absorbers — and offer some tips on how to tow as safely as possible.
Leveling Your Load
Available from automakers and aftermarket suppliers, airbag systems are offered in two different configurations. One type uses airbags as an extra support spring to standard leaf-, torsion- or coil-spring suspension systems. The other airbag system is a complete air suspension, meaning the vehicle uses airbags in place of other springs. Air suspension systems are usually found on premium vehicles and trim packages. Four-corner air suspensions can be had on the Ram 1500 pickup truck and Jeep Grand Cherokee SUV; it can also be ordered as a supplemental spring for tow-hungry pickups such as the Ram 3500.
Self-leveling shock absorbers are a less popular way of leveling a vehicle. Self-leveling shocks replace standard shocks and generally work with a specifically designed leaf or coil spring. These self-adjusting systems use the force from bumps and dips in the road to adjust the height of the vehicle; the current-generation Ford Expedition SUV is offered with this type of shock absorber.
Many automakers offer one or both systems, especially on vehicles capable of towing. The Chevrolet Tahoe [JB5]and Suburban SUVs; GMC Yukon and Yukon XL SUVs; Ram 1500, 2500 and 3500 pickups; Toyota Sequoia and Land Cruiser SUVs; Ford Expedition; and Jeep Grand Cherokee SUVs are among the vehicles that offer load-leveling systems.
However, both systems can hide how much load or force is being placed on the vehicle, creating an unsafe situation. If your suspension always looks level, even if it's overloaded, then you won't know if you have the right amount of weight distributed over the trailer axles or the maximum suggested weight on your hitch.
The Risk You Take
If you do not follow your trailer's or tow vehicle's weight limitations and distribution recommendations, and your load-leveling technology hides the situation, you could face several serious consequences.
- The rear axle weight rating of a vehicle can be exceeded without the driver noticing. This can add more wear and tear to the axle, tires and brake components, and potentially lead to a catastrophic failure.
- The load-leveling components themselves might be damaged from overloading scenarios. When airbags or self-leveling shocks are overloaded, they both run the risk of internal damage by generating excessive heat. Both have valves, reservoirs and seals that can leak or break when the vehicle is overloaded.
- Improper load distribution can impact the front axle and affect steering. Most people don't think about this when towing, but when a truck pulls a heavy load the rear axle becomes a pivot point, reducing the load on the front axle. This can be dangerous as it decreases the ability to steer and brake in predictable ways. Often a driver won't notice the reduced weight on the front axle until driving over a bump, which causes what's called steering "float." Reduced weight on the front axle also can create braking issues during hard or emergency braking; the front wheels can lock up or trigger the antilock braking system quickly without sufficiently slowing the vehicle.
There are solutions to these problems; here are five things that we recommend.
Measure Your Tongue Weight
Tongue weight is the downward force that the tongue of the trailer applies to the hitch of the tow vehicle. If you have any question about what the tongue weight is on an empty or loaded trailer, then it needs to be measured.
There are a few ways to do this. One is to buy a scale built specifically for measuring tongue weights. It is placed under the tongue jack of your trailer. Depending on the size of your trailer, you can also use a bathroom scale with the fulcrum and lever. Other options include going to a commercial scale to measure the tongue weight or buying a hitch-ball mount with a built-in scale.
A good rule to follow is to load the trailer so that the tongue weight is between 10 and 15 percent of the total trailer weight. If you are towing a car trailer, you might have to move the vehicle a little bit forward or back on the trailer or change where the Dutch oven and extra water tanks are stored in your travel trailer. Make sure everything is strapped down.
Properly Load the Trailer and Tow Vehicle
Do not exceed your tow vehicle/trailer weight ratings. Find out the tow vehicle's axle ratings, gross vehicle weight rating (the weight of the vehicle plus how much it can carry in passengers and cargo) and gross combined weight rating (maximum allowable weight for towing a trailer, including passengers and cargo). The first two will be on the door tags; the third you'll have to find in the owner's manual, from dealer or on the manufacturer's website. Often, a load can be shifted between axles or between the tow vehicle and trailer to ensure that none of these ratings are exceeded.
Level the Trailer
If a trailer has more than one axle, it needs to be level when being towed. Adjustable trailer hitches and ball mounts are quite helpful since they can be set to the proper height. To level the trailer, park it on flat ground and measure from the bottom of the frame to the ground at the front of the trailer and at the rear of the trailer. These two measurements should be the same when the trailer is attached to the tow vehicle. Having a level trailer ensures that the trailer axles and tires wear and distribute weight evenly; it also will improve how the trailer tracks behind the tow vehicle.
Measure the Height of the Fender
The distance from the front fender to the ground is a rough indication of how much weight is on the front axle. The actual measurement is vehicle specific as it depends on the spring rate of the front suspension; spring rates can vary for different packages on the same vehicle and model year. It may take several times towing different tongue weights before you figure out the height at which your vehicle will be most comfortable and safe. Take this measurement before and after coupling the trailer in the same location every time.
Use a Weight-Distribution Hitch
Most vehicles require the use of a weight-distributing hitch when towing more than 5,000 pounds; check your owner's manual. A weight-distribution hitch, especially one with built-in sway control, is always the best option when pulling a heavy trailer.
Setting up a weight-distribution hitch takes a little more time when used with a load-leveling suspension, but when set up properly, it distributes weight between all the axles of the tow vehicle and trailer. This includes restoring or even increasing the weight on the front axle of the tow vehicle. A weight-distribution hitch usually will provide better handling and better braking ability than a normal hitch or ball-mount setup because it does a better job of distributing the weight over a wider area. Weight distribution is so important that many automakers require a weight-distributing hitch to reach the maximum towing capacity of the vehicle, as in the case of the Ford Expedition.
Cars.com photos by Matthew Barnes
Weight-distributing hitch bar designed to redistribute heavier tongue weights.