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Junior Member
Join Date: Jun 2024
Posts: 23
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Forces of Nature...
Greetings my Fellow Romans:
I'm fairly new to RV forums and find them very informative. However, in some cases, informative in a worrisome way. I've been around the sun seventy times now, and in my travels, I have learned that Mother Nature has put limits on everything in this life. And that includes the weight, balance, and operation of our RVs.
Some of the great thinkers of the past 2,000 years or more figured out that weighting and balancing on a fulcrum is one concept we all need to consider in our everyday lives.
One of the greatest of these thinkers was Sir Issac Newton who gave us a vast amount of knowledge about a mass in motion, whether it be a cannonball in flight, or an Apollo spacecraft on the way to the moon on a free return trajectory. But there are still limits to the cannonball and the spacecraft. And some of the same limiting forces apply to our RVs.
Yet, when I read threads on this, and other, RV forums, I find that there is a "camp" that believes it's acceptable to exceed these limits and still accomplish the objective of arriving at a destination safe and sound. This should concern everyone. I'm certainly concerned. I may be the one hit from behind and pushed off into the ditch by someone of that "camp" who cannot stop in time while going down the mountain. Or, perhaps, when they have a failure of a critical part while they're passing me.
I'm not a vehicle engineer. I was a radar technician in an earlier life. But I do understand that the limits of our vehicles that the engineers and builders of the vehicles give us should never be exceeded. We have limits for Gross Vehicle Weight, Max Axle Weight, Max Tire Load, Max Trailer Weight, etc, etc. And the list of limits just keeps on going... And it honestly is possible to live within all the limits we have. Not only is it possible, but it's very reasonably possible. If you want to pull a 20,000 pound trailer that puts 4,000 pounds on the fifth wheel hitch, you just have to use a TV built to handle such a combination. Most of us realize that the RV world just ain't cheap. lol.
There seems to be a common belief of this "camp" that if you are under the Max Load Rating of your tires, that it's okay to be over the Axle Weight Rating. Or if you're under your Max Weight Rating from the hitch manufacturer, it's okay to be over the Max Tongue Weight set for the tow vehicle.
It's like if you put a hitch rated for 1,200 pounds under your vehicle that's rated for a max tongue weight of 1,000 pounds, and you put a 1,200 pound tongue weight on it, you're good to go because you're not over the max hitch weight from the hitch manufacturer. What am I missing here?
Damage from over-stressing materials in our world is cumulative. That is, it adds up over time and repeated misuse until one day, the bridge collapses into the Mississippi River killing 100 people.
This brings up yet another point that everyone who tows on a receiver hitch should know and understand. It comes from another one of the great thinkers long before Newton. And that is, the balance of forces. Believe it or not, within a weight range, the weight isn't the primary concern in balancing forces. It's only one factor. The objective is to balance forces, or "moment". The moment is the weight (mass) X the arm (the distance from the fulcrum).
For example: A tongue of 500 pounds (mass) on a ball that is 36 inches (arm) rearwards of the rear axle (fulcrum) = 1,800 in/lbs of moment that must be balanced from the opposite side of the fulcrum. We must have an increase of 1,800 in/lbs forward of the rear axle. The only place to get this is to borrow it from the front axle. Since we cannot change the arm (wheelbase of the vehicle), we have to consider the mass. So, if we take the moment of 1,800 in/lbs and divide by the wheelbase of 180 inches (arm, distance from the fulcrum), for example, we see that we will balance the moment simply by a transfer of 100 pounds (mass) off the front axle onto the rear axle.
After the trailer is hooked, the front axle weighs 100 pounds less and the rear axle weighs 600 pounds more, not 500 lbs, 500 lbs of tongue weight + 100 lbs of balancing weight from the front axle.
This transfer of 100 pounds does not affect the gross weight of the tow vehicle with the trailer hooked. It's just a transfer from one axle to the other. On weighing the combination again, you will see the Gross Weight of the tow vehicle is only 500 lbs heavier, but the rear axle weight has increased by 600 lbs
This balancing of moments may explain some questions of those who noticed a discrepancy in rear axle weight. Make sure your rear axle and tires aren't overloaded.
As can be understood from my example above, if you know the distance from the axle to the ball, you can make a "ballpark" estimate of how much tongue weight your tow vehicle might safely handle before you throw down a fist full of dollars. But keep in mind, you may still have to play with your loading to stay under all the limits. Naturally, I do not suggest you try cutting it very close. After all, you are just looking for a "ballpark" estimate.
I pull a 21,000 lb 5th wheel toy hauler with a 3500 class diesel dually. I'm under all of my weight limit ratings for everything. All of my scaled weights are posted somewhere in this forum. I forget where.
In the spirit of sharing information and helping others here be safer going down the road, I would be open to PMs, email, or even phone conversations on this topic. However, I'm fairly new here and I don't believe I can send my phone number or email address to anyone yet. Perhaps one day.
I would be interested to read your comments if you would reply to this post.
Dave
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