RV Weight Part 1: Ratings & Why You Should Care

(Cover photo from www.fraserway.com.)

I’ve been a backpacker since I was a kid, and one thing I learned early on is: Our shit is heavy. Always much heavier than we think. An ounce here, a few grams there, and next thing you know, you’re lugging a 70-lb. backpack up a mountain. This happens when we load up an RV too, and even more so when we are full-time. Most people assume that space is the most limiting factor when moving into an RV, but in fact it is weight.

This is the first post in a series about towable RV suspensions and weights:

RV Weight Part 1: Ratings & Why You Should Care (this post)
RV Weight Part 2: Visiting The Scales
RV Weight Part 3: Suspension Upgrade
RV Weight Part 4: Fixing the Mistake

Unfortunately, fully understanding the implications of your RV's weight is not a straightforward subject. It involves learning a fair bit of new information, plus dealing with a lot of numbers and ratings with confusing acronyms, and on top of it all, the process is usually iterative  most of us can't just load up our RV and drive away. You have to check, adjust, and re-check.

The way RV dealers and salespeople handle this subject doesn’t help. A lot of rigs don’t have nearly the capacity that their owners are led to believe. Without going any further into that rant, I’ll just say this: Most rigs will exceed their weight ratings if all the available space (cupboards, compartments, shelves, etc) is actually filled. Not even crammed full…just…filled.

My next few posts will discuss weights and ratings for RVs. Because I know this is not a "fun" subject, I'm going to start by talking about why you should even care — and hopefully that will be enough motivation to get through the acronyms and calculations. I'll also relate how we realized — then fixed — some issues with the Toaster's weight.

Where do ratings come from?

Putting ratings on products is the kind of thing I used to do as an engineer, so I want to talk about it a little. I think the XKCD comic below covers the disparity between how most folks think ratings are determined, and how they are actually determined:

Actually calculating product ratings is usually mathematically difficult — often quite impossible, in fact. The physics are nowhere near as simple as folks assume, and the variables are numerous. Even the fancy computers that render fantasy movie landscapes can’t solve the simplest-seeming simulations. Yeah, reality (aka differential equations) is a bitch.

The most practical approach is to test actual products at various standardized loads under simulated conditions, while applying a “safety factor” to account for whatever the test may not cover. Because testing is expensive, those tests and safety factors are (often) determined by looking at past product failure rates and analyzing them statistically. So over time, manufacturers (and the agencies that regulate them for safety) come up with idealized tests, standards, and calculations that they all agree upon as being adequate.

And they are adequate. It’s the best anybody can realistically do. Because there is no such thing as 100% in the real world. But remember that all this is predicated on assumptions about how these products will be used. Those assumptions are tied to the way the manufacturer intends the product to be used, and as RV owners, we need to be honest with ourselves about how well our usage resembles those intentions. RV's are fundamentally NOT designed for daily, full-time use. And you can bet the engineers are not thinking about godforsaken boondocking sites down nasty dirt roads when they create RVs or their components! This thought is enough to make me want to keep within the ratings.


So these ratings are applied by manufacturers to tell us what our equipment is capable of. But what happens if we exceed them? That depends on how much the rating is exceeded, how often that's done, and how lucky you are. What could possibly happen?


It's possible that nothing will happen at all. I frequently encounter people who are breezily content with their setup based entirely on the fact that it hasn't broken yet. This is a nice illustration of the normalcy bias, and a solid mistake. If you know your rig isn't safe but it "hasn't broken yet", you should feel more nervous, not more safe.

Rapid Wear

The next "least bad" thing is that your equipment wears out faster. Wheel bearings, suspension components, brakes, transmissions...this can get expensive, but not necessarily deadly. Rapidly wearing components are a symptom, and it's wise to ask why they are wearing so quickly. This is where the story begins with the Toaster.

After being on the road for several months, I realized our trailer was riding a little nose-high on the truck. It was a subtle tilt, so I didn't notice it at first when we were new at RVing. But it was there, and there was no adjustment left in the hitch, so we couldn't do anything about it.

This would normally be considered a perfectly-level trailer, but not in our case.

This would normally be considered a perfectly-level trailer, but not in our case.

You may be thinking that I'm nuts for calling that trailer un-level. It was, in fact, riding very nicely on our truck and in most cases, there would be nothing at all wrong with our setup. But there's an extra factor to consider: Our trailer was already at the maximum rated axle weight. The slight tilt meant the rear axles were carrying a bit more weight than the front ones. Normally such a small tilt would be a non-issue, but in our case even this tiny difference between the axles was exceeding the rating. This was probably exacerbated by the age of the suspension (about 15 years). So the rear axle was overloaded, which caused it to deflect too much, resulting in excessive negative camber of the wheels. As a result, the inside of the rear axle's tires were wearing rapidly.

One of our rear axle's tires. It has less than 20k miles on it. You can see the tread depth on the inside edge (arrow) is much shallower than on the opposite edge. If we had continued to run this tire, it would have blown out.

One of our rear axle's tires. It has less than 20k miles on it. You can see the tread depth on the inside edge (arrow) is much shallower than on the opposite edge. If we had continued to run this tire, it would have blown out.

Canary Failures

Next is blowouts. Many people seem to treat blowouts as if they're just an unavoidable eventuality of RV ownership. I swear some people actually sound boastful when they talk about how many they've had. No! When a tire on your rig EXPLODES, that means something is wrong. Maybe they are just improperly inflated, or maybe only the tires are under-rated...but usually the tire is rated to match the axle it's on, so that means the axle is also over-loaded. Axles CAN break off moving rigs - this actually happened to friends of ours!

If you get a blowout, regard it as a warning from the Universe. Time to get very serious about finding out what's wrong, because the next time you call roadside assistance, it might be because your rig is on it's side in the ditch.

Catastrophic Failures

The worst case is that your rig's weight problems make you crash. As full-timers, we have the unique opportunity of being able to destroy both our transportation AND our homes all at once. If your RV is a towable, it's even possible that your weight is within "legal" limits, but the distribution is off, leading to dangerous handling characteristics. A trailer putting too much weight onto the tow vehicle can lead to uncontrollable oscillations and rollover accidents. At the same time, not transferring enough weight to the tow vehicle can set up weird braking behaviors and violent bouncing at highway speeds which also increase the chances of a wreck. A poorly-timed blowout can lead to a wreck just as easily as a misbehaving trailer. What if you got a blowout on a twisting, steep downhill? Or while you were trying to make a normally-safe stop in traffic?

I came across this video on Facebook, which demonstrates very well how simply changing the distribution of weight in a trailer can impact handling characteristics. I know it doesn't seem like a big deal on that little toy car, but in real driving conditions (wind, rain, steep grades, uneven pavement), these "little things" add up and can lead to really unpleasant wrecks.

The Lecture

I know this all seems like making a big deal about "unlikely" events. Remember that you are piloting anywhere from a few to a dozen tons of stuff down the road. Do you really think you can do that safely without even trying a little bit? Yes, this is a little overwhelming to consider, and yes it will involve doing some math and looking up specifications. But considering what's on the line, I think it's very much worthwhile.

Do a google image search on "RV trailer accident". There are plenty of hits (and they include truck-campers and motorhomes, too). These are not "freak" accidents that only happen once in a while.

Remember this: You are the sole party responsible for your rig. If your rig is unsafely loaded and causes an accident, the RV dealer, RV manufacturer, tow vehicle manufacturer, and hitch manufacturer are not at fault. You are. Consider that if you crash your rig, you can hurt people besides yourself, such as those behind you on the highway. That is your responsibility: Morally, legally, and financially.

So ask yourself: Do you think your tire manufacturer accounted for those one or two (dozen) parking lot curbs you smeared your trailer tires along? Was the guy who spec'd the axles on your coach thinking about 10 mile long jeep roads to boondocking sites? Did your tow vehicle’s engineers design the rear suspension to be any more robust than absolutely necessary to meet specs, considering the immense cost pressures they are under? How much margin of safety do you reckon you actually have, and do you really want to exceed those ratings?

Please weigh your rig!

To check that you're operating your rig safely, the first step is to get it properly weighed. My next post will talk about the weighing process, and what to do with the numbers that come out of it. I'll also talk some more about the Toaster's weight problem.

We respect the ratings of our equipment. Because even if Good Sam covers the tow, I don’t want to be this guy:

Read the story behind this crash at Fifth Wheel St.

Read the story behind this crash at Fifth Wheel St.

That's a bad day, any way you slice it.

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