By Roger Marble
I’ve been monitoring a forum thread about a guy who wanted to hang a 250-pound toolbox off a mount from the rear bumper of his trailer. He just didn’t understand the implications of changing the hitch load if he made such a change or the shift in tire loads between axles.
This 30-second video from Facebook shows the potential of not doing the calculations and for ignoring science.
Distance from axle to toolbox could be a serious issue when you consider how levers work.
I have also seen some Class C motorhomes with platforms attached to the trailer hitch receiver. Some have mobility scooters on them, some have toolboxes and some even have motorcycles. These items might be 100 pounds, but I am afraid that the total might approach 500 pounds in some applications. While the hitch and platform might be rated for 500 pounds or more, the back end of the RV may have lower limits.
Load capacity is limited by the weakest link or component
It is important to remember that just as with axles, springs, and tires, the load capacity is limited by the weakest link or component. For axles, the weakest component is many times the tires. You may have an axle rated Gross Axle Weight Rating (GAWR) of 3,000 pounds and the tires may only be rated for 1,510 pounds. But swapping the axle with a 4,000-pound unit will not raise the GAWR unless you also change the tires and probably also the springs, brakes and spring mounts.
This same situation can occur for the hitch. Class C motorhomes are many times built on the “cutaway” frames of standard vans. But the RV company extends the wheelbase by cutting the rear of the frame then welding in a couple pieces of steel to make it longer. This does not result in a longer-but-equal-strength structure. In fact, it may mean the total frame strength is now lower.
Back to the question of what happens even if you don’t have load limitations on the frame or receiver. Hanging weight off the rear bumper does TWO things. First, it obviously increases the load on the rear tires. Second, it decreases the front tire loads and transfers that load onto the rear axle and tires. You need to be sure that this addition is not overloading any of your tires, as both of these conditions are potentially dangerous.
Have a tire question? Sign up for Roger Marble’s new Facebook Group: RV tire news, information and discussion, hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.