Calculating the safe towing weight is essential to any hauling operation. To complete the task successfully, you must take the time to assemble all of the necessary weight measures and information about your specific vehicle, trailer and hitch. This will include research using owner manuals and tags, along with the careful use of an accurate personal scale, or a trip to a public scale. It is worth the time and effort, however, because a miscalculation may either lead to damage to the vehicle and cargo, or worse, injury to the driver and passengers.
Using the vehicle's owner manual, look up and record the gross vehicle weight rating, or GVWR, the gross combined weight rating, or GCWR, the vehicle's maximum loaded trailer weight rating and its maximum tongue weight rating. Finally, record the vehicle's rear gross axle weight rating, or RGAWR.
Some of this information may be available on a tag on the driver's side door of the vehicle.
Determine the actual weight of the loaded towing vehicle. You can accomplish this by adding up the actual weights of the driver, passengers, cargo and fuel with the kerbside weight of the vehicle. Otherwise, you can take the loaded towing vehicle and trailer to a public scale at a moving company or a truck stop to get a completely accurate actual weight.
Measure the actual rear axle weight of your fully-loaded towing vehicle without the trailer attached, the actual weight of the fully loaded trailer and the actual tongue weight of the trailer. The tongue weight can also be determined by placing the tongue of the loaded trailer on a bathroom scale set up at the level of the hitch. The tongue weight should be about 10 per cent of the weight of the loaded trailer.
Select a percentage of the towing vehicle's maximum safety ratings as a safety margin. A minimum of 20 per cent is recommended. Select a safety margin of at least 15 per cent of the vehicle's tongue weight rating. It is better to allow a generous margin on the weight ratings to ensure greater safety. You can subtract your vehicle's actual weight, and its rear axle weight, from its gross weight rating to determine its safe tongue weight. The tongue weight should be no more than 15 per cent of the actual weight of the loaded trailer.
Once you have all or most of these measurements in hand, you can enter them into an online calculator at the website ChangingGears.com, and you will be able to determine the exact towing weight that is safe for your vehicle.
Exceeding the towing capacity of a vehicle can lead to engine damage, unsafe handling conditions while under way, and, in the worst-case scenario, a failure of the towing hardware, leading to a serious accident.