What Is Towing Capacity?

Unless you're an experienced driver of a large truck or fifth-wheel vehicle, your inclination might be to look in the guidebook that came with your truck and be satisfied with the towing weight specified in that. There are many variables that factor into towing capacity, and the one that isn't covered in the manual that came with your vehicle is your experience and common sense. Safety is rule No. 1 for you, the occupants of your vehicle and others on the road.

Definition

Towing capacity is how big a trailer you can hitch to your vehicle and drive it safely. To determine the towing capacity of your vehicle, you must first figure out the combined weight ratio, which can be found in the vehicle manual and on the inside of the driver's-side door. Add the weight of everything packed in the truck, the weight of the towing vehicle plus the fuel and passengers. You can determine this using a scale at many truck stops or landscape yards or do the calculations yourself by weighing everything and everyone that will be in the vehicle plus the weight of the vehicle. On the fuel weight, 1 gallon equals 8.45 pounds, so multiply that number by the number of gallons your fuel tank holds. Now, subtract the loaded weight of the towing vehicle from the combined weight vehicle capacity and it will tell you how much weight you can tow.

The Manufacturer's Recommended Towing Capacity

The recommended maximum towing ratio is included in the manual that came with your vehicle. It's likely that your first thought is that the towing-weight capacities are on the low side. And they may be. However, follow them anyway, especially if you have never towed anything behind your vehicle. There are many conditions and variables that you probably haven't thought about. If something went wrong, such as an accident, and you didn't heed the manufacturer's recommendations, there is a good chance you would be found liable if motor-vehicle laws are enforced and that the extra weight could cause more damage and harm.

Mass

In 1998, the federal government passed a a law limiting the mass of a vehicle that is being towed. Other factors besides the combined-weight vehicle capacity must be considered. One is the ball weight. The ball weight is the weight that rests on the ball of the hitch. Since the vehicle you are towing has at least one axle, that will affect weight distribution of the unloaded vehicle to be towed. It must be attached to the towing vehicle, usually by means of a ball hitch. You must determine the weight of the loaded towed vehicle and how much weight will rest on the ball attachment, because that weight will become part of the driving vehicle and will affect how the towing vehicle operates, putting an extra burden on the towing vehicle's suspension.

Brakes and Suspension

Starting and pulling a towed vehicle is the easy part. The hard part is keeping it under control, particularly driving downhill and when you have to slow or stop both vehicles. Remember, it's not just one vehicle that you are driving, but two. So not only do the brakes carry twice the load, so does the suspension in the towing vehicle. Many towed trailers are equipped with their own braking system, but many are not. If what you plan to tow doesn't have its own braking system, that responsibility falls on the towing vehicle, so the brakes should be heavy-duty and designed for the kind of towing you will be doing. If the towed vehicle has its own braking system, you may tow one and a half times the towing vehicle's mass. If there are no brakes on the towed vehicle, then a 1-to-1 ratio applies.

Other Considerations

When driving a towed vehicle, keep in mind the weight distribution of cargo. The more that can be centered over the axles of the towed vehicle the better, because it will help create an equilibrium between the two vehicles. The same goes for centering as much cargo as possible to avoid towing an unbalanced load, which can tend to pull the towing vehicle in one direction or the other, which can be dangerous when driving in high cross winds and when bufffetted by the draft of another large passing vehicle.

References

• Common sense tips on towing from the National Caravan and Recreational Vehicle Towing Guide
• Trailer loading and towing guide
• Tow vehicle specifications explained.