If you think you can upgrade your axles to increase your RV’s maximum weight capacity, think again.
Many RV owners have purchased a Brobdingnagian house-on-wheels only to discover that by the time they fill up the cabinets and storage nooks, the RV is already stretching its suspenders!
As I’ve written about before, insufficient cargo carrying capacity (CCC) is a major problem for many RVs: most large travel trailers, Class C motorhomes, and some 5th wheels and Class A coaches. You can find 30-ft rigs with less than 1,000 lbs of cargo capacity!
Ergo, why not upsize the axles to increase the weight capacity? It’s a reasonable question. Let’s walk through the answer[s].
Can I Upgrade My Axles to Increase My RV’s Cargo Carrying Capacity?
Short answer: No. The official GVWR of your RV is decided by the manufacturer. No aftermarket modification you make will EVER increase this number – although you can certainly decrease it!
This is for two reasons.
- No self-respecting manufacturer is going to open up a Pandora’s Box of legal liability by agreeing to an increase in GVWR beyond the original design limit.
- You don’t know what the limiting design factor was. Was it the axles? The tires? The vehicle driving dynamics? The coupler weight rating? The tongue weight? Was the frame designed with a 10-year or a 50-year desired lifespan?
Even if you call a manufacturer, like Lippert, and walk through your modifications, a manufacturer will never put their stamp of approval on an aftermarket GVWR increase.
In some cases, a final-stage manufacturer (such as a certified upfitter) can make modifications to GVWR/CCC within an approved range, but that’s beyond the scope of what we’re talking about.
And while this may sound annoying, it’s really just responsible business practice.
However … I am not writing this blog post as a manufacturer (in which case I would probably stop here). So let me walk you through some of the considerations (and myths) behind adjusting your camper’s weight capacity.
Fact: Suspension Upgrades Don’t Change Sprung Weight
First of all, let’s talk unsprung weight.
- “Sprung” weight is carried by a suspension. It’s everything above your axle: your frame, walls, roof, slide-outs, kitchen, cargo, etc.
- “Unsprung” weight is not carried by a suspension. It’s made up of the components of the suspension: the axle, brakes, hubs, tires, etc.
When you upgrade your axles, this typically doesn’t affect sprung weight. If you upsize from 5,200-lb leaf-spring axles to 7,000-lb leaf spring axles, along with the corresponding tires and rims, then perhaps you’ve added 200 lbs overall – but that weight is within the suspension, not on top of it.
This is good news! Yes, your RV now weighs more overall, and that affects whether your tow vehicle can handle it … but the cargo carrying capacity of your RV remains the same. You haven’t taken away any capacity. Hurray!
It’s important to note here that upsizing your “axles” is just a colloquial way of saying, “Replace your entire suspension.” The weakest link breaks the chain, so you need to ensure that your entire suspension system – axles, hangers, springs, hubs, studs, rims, tires, etc. – are all rated for the GAWR of the new system. (And in fact, your tires should have an additional 10% weight capacity.)
But I know what you’re thinking. “Why doesn’t my cargo carrying capacity increase, though? I just upgraded the axles to 7,000 pounds, after all!”
Doesn’t seem fair, does it?
Myth: The Frame Is the Limiting Design Factor
I have seen on several forums some comments that argued one could not increase GVWR or CCC because the frame, not the axle, was the limiting factor.
This is not a justifiable assumption. It may or may not be true.
It would be a mistake to assume that your RV chassis was designed so that every part was sized for its intended load. That’s simply not true.
The same chassis may be outfitted for a wide range of weight capacities. A manufacturer doesn’t design a new chassis for a 6,800-lb RV; they’ll recycle and tweak an existing chassis rated for 7,400 lbs. You get the idea.
This is smart business practice. By recycling common designs, manufacturers significantly cut costs, which get passed down to you.
But it also means that you can’t assume you know what the minimum or maximum weight range of the frame actually is!
In other words, your frame might be maxed out at its current GVWR. Any more weight, and you will significantly shorten its lifespan. Or it could be overbuilt, and a few hundred pound extra wouldn’t hurt it.
But again, no one will tell you. I can’t even tell you – it totally depends on the RV. For instance, check out the picture below. The main rail has been reinforced with a 2×2 steel tube, V-braces at the central hanger, and bracket at the I-beam flanges. Just because you increase your axle capacity does not mean the rest of the frame was made to match!
And I would caution you against trying to reverse-engineer the capacity of a frame simply by comparing material sizes. I often see people saying stuff like, “Well, my frame has 10-inch I-beam main rails, and this other trailer rated for 1,000 lbs more also has 10-inch I-beam main rails, so I should be good to go!”
That’s a very dangerous assumption. For one, the strength of a beam varies with its length, not just its cross-section. For another, how do you know the limiting factor isn’t the tongue, and not the main rails? Or perhaps the other 10-inch I-beam main rail was reinforced above the spring hangers for additional weight, and yours is not?
Frustrating, isn’t it?
Fact: Load Distribution Matters!
I read a conversation on one internet forum where the OP planned to upgrade his axles and keep all the extra weight in storage cabinets close to his axle. His rationale was that the extra weight would be centered above the axle, therefore not stressing the rest of the original frame.
There’s definitely some truth in this! Because the way you load your RV matters.
At one extreme, if you loaded all your weight close to the front, then you’d overload the tongue and probably bend it in half like an origami paper crane.
At the other extreme, if you loaded all your weight close to the rear, then you’d make it about 200 yards out of the driveway before fishtailing and porpoising drove you into a ditch.
So the idea of loading your cargo so that the bulk of the weight is over the axles is very, very smart.
- For trailers, the ideal center of gravity of your cargo is usually just in front of the axle, so that about 10-25% of your cargo weight is shared with the tongue.
- For motorhomes, the ideal center of gravity of your cargo varies between FWD and RWD motorhomes. The obnoxious rear overhangs of many motorhomes complicates matters, because sharing weight equally between the front and rear axles allows the rear overhang to act as a big, pushy lever.
Unfortunately, if your frame was the limiting design factor, then this workaround would still fail …
So What’s the Final Word?
I’m starting to talk in circles, aren’t I? As an engineer, I can’t arbitrarily condone an increase in your weight-carrying capacity. Sorry. I don’t know your RV!
However, I think upgrading your axles so you have a greater margin of safety when traveling at full capacity is an excellent idea!
At full capacity, many RVs are overloaded on one side or another. By increasing your suspension GAWR, you give your RV the extra “cushion” it may need to safely carry its maximum cargo capacity.
Plus, if you do accidentally find yourself overweight by a few hundred pounds, that bigger, beefier axle will buy you a lot of peace of mind until you can unload.