When Towing, the Weakest Link Breaks the Chain

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I contend that towing an RV has ruined more relationships than Tinder.

RV weight ratings are cryptic, overlapping, muddled, and nuanced. What’s the difference between curb weight, factory weight, dry weight and unloaded vehicle weight? For some vehicles, all four numbers are identical. For others, all four are different!

If it makes you feel better, it’s worse inside the industry. We deal with FMVSS, enforced through the National Highway Traffic Safety Administration (NHTSA) agency, which is part of the Department of Transportation (DOT). And per RVIA compliance regulations, we must follow National Fire Protection Agency (NFPA) 1192 regulations, ANSI LV, the National Electric Code (NEC) – also known as NFPA 70 (possibly along with ANSI 119.5) – and ensure our products are listed by their Nationally Recognized Testing Laboratory (NRTL) …

Anyway …

I’ve written this sermon article to preach a simple message:

When towing, the weakest link breaks the chain.

Sounds simple, right?

Maybe. But in my humble opinion, many RVers – particularly people who have never towed before – don’t understand all the links in the chain. If that’s you, you might not know what to look for!

This article is about your safety: yours, mine, and the guy driving behind you.

Core Concept: The Weakest Link!

Imagine you’re fishing at a lakeshore.

You cast a line made from three sections: a 20-lb fishing line section, a ⅛-inch steel cable, and sewing thread.

You hook a 3-lb smallmouth bass. What will happen?

The line will break, of course! And what will snap first? Certainly not the steel cable!

Answer: the sewing thread, of course.

The same logic applies to towing.

The engine, tires, brakes, axles, frame, rear bumper, hitch, ball – every single component must be strong enough to tow the rated load!

If a single bolt holding the receiver hitch to the tow vehicle’s frame rusts through and breaks, that could launch a zipper-like reaction to total failure!

If you put a tiny Class I hitch on an F-250 diesel truck, you are limited by the hitch, even though the truck can pull 10x as much!

Let’s look at some examples.

… Actually, before we read some examples, here’s an important tangent about weights vs ratings.

Core Concept: Weights vs Ratings

A lot of the fuzziness around RV weight ratings comes from confusion between maximum ratings versus actual weights.

Most acronyms are either a RATING or a WEIGHT.

  • Rating = maximum capacity
  • Weight = actual measured load

If I step on my bathroom scale and it reads 210 lbs, that’s the WEIGHT.
The scale itself might have a maximum weight RATING of 300 lbs.

So if an RV has a GVWR of 12,000 lbs, that’s a RATING.
If you load the camper for a weekend and it weighs 11,732 lbs, that’s the actual WEIGHT.

If you’re a little confused about which is which, I highly recommend this infographic and article from Curt Manufacturing. It’s easy to understand, and I think the visuals are pretty intuitive.

P.S. While there is an engineering difference between weight and loads, customers often use both terms interchangeably. Do yourself a favor and call each by its proper name.

How The Weakest Link Plays Out

EXAMPLE 1: Degraded Hitch Pin

For instance, if you have a hitch receiver on your pickup truck, then your ball mount is held inside the receiver by a simple part: the hitch pin. It’s a simple, solid steel cylinder barrel, ⅝” diameter. It’s held in place by a spring clip pushed through a hole in one end.

What if … you forget to put in the spring clip?

Or what if, after five years of dragging your camper through the mud, snow and sand, your hitch pin finally gives up the ghost?

Yes, it has happened.

And suddenly, the only thing holding your camper to your tow vehicle is the two safety chains! (You did cross them in an X underneath the coupler, didn’t you?)

EXAMPLE 2: Buyer’s Remorse

Or let’s look at a buyer’s example.

You want to buy a camper that weighs 6,000 lbs with a factory tongue weight of 672 lbs. You “look up” the towing capacity of your truck online: 8,500 lbs maximum towing capacity with an 800 lb maximum hitch weight.

You use the Changing Gears Towing Weight calculator to verify that your truck can actually tow that big of a camper when loaded to your specifications, and everything checks out!

… Except you never took the time to physically inspect your hitch. If you had, you would have noticed that your truck didn’t come with the factory towing package. It has an aftermarket hitch installed by a U-Haul somewhere, and it’s a Class III hitch only rated for 6,000 lbs towing and 600 lbs hitch weight. Plus, no transmission cooler.

If you’re lucky, you’ll just burn up your transmission. If you’re unlucky, you’ll wind up in a ditch. If you’re really unlucky, someone else will wind up in the ditch instead.

EXAMPLE 3: Off to the Mountains!

The weakest “link” in the towing chain isn’t necessarily a mechanical component. It could be weather, road conditions, or elevation!

Most automotive manufacturers mandate that towing capacity decreases by 2 percent for every 1,000 feet altitude increase above sea level.

That’s not common knowledge. Let’s see how it plays out.

You live in Springfield, Missouri (elevation: 1,306 feet). You’re about to visit the Greater Yellowstone area! Part of your travels takes you up, up, and up the Beartooth Pass, an All-American Road on U.S. Route 212 in Montana and Wyoming, just northeast of the National Park. It’s 10,947 feet in the clouds, and one of the most beautiful places you’ll ever visit!

That’s an elevation difference of 9,641 foot, or roughly 10,000 feet. That means you lose 20 percent of your maximum towing capacity!

So your Chevrolet Tahoe, which could tow 7,900 lbs, can now only tow 6,320 lbs. Which means you’ll be effectively overloaded towing the entire Beartooth pass, and a good part of your cross-country travel, too.

EXAMPLE 4: Everything But the Kitchen Sink

After months of planning, it’s finally time: The Great American Road-Trip. The St. Louis Arch, the South Dakota badlands, the New Mexico White Sands Monument, Garden of the Gods – you’re going to see it all!

So you pack three kids and five weeks’ worth of gear into your 28-ft fifth wheel, and away you go!

15 days later, you’re all sitting despondently inside Bob’s Auto Repair Service. Bob is saying your rear differential is shot, your tires are wearing unevenly, and three of the studs on your rear driver’s-side wheel have sheared off, so you’ll need a new rim, too.

What happened?! You weighed your camper – it was 7,725 lbs, only 25 lbs over the GVWR! No biggie, right?

And you have a freakin’ 2021 Ram 1500 Warlock* with the 5.7-liter Hemi V8 (a Hemi, for Pete’s sake!) with 1,633 lbs of payload and 8,650 lbs of towing capacity – that has to be enough capacity, right??

…. But was it?

  • Your king pin weight was higher than you anticipated. Due to the way you loaded your trailer, the king pin weight was 22 percent of your GVWR, almost 1,700 lbs. Still within the acceptable range for a 5th wheel (15-25 percent), but definitely high.
  • You also didn’t factor in the full weight of the passengers, snacks, and overnight backpacks in the cab (plus the loaded tool chest in the bed). Altogether, you added another 525 lbs to the rear axle.
  • That’s a total of 2,225 lbs, well above your maximum payload. Add in the rough roads, the occasional speeding above 70 mph (you were just passing, I know), the age of your pickup, and your truck just couldn’t take it anymore.

But since you only weighed the camper itself and compared the loaded 5th wheel weight to the tow vehicle’s (ideal) maximum towing capacity, you missed all this.

Here’s another article I wrote about habitually overloaded trailers.

EXAMPLE 5: “What’s That Rolling Away?”

Some potential failures are invisible to the naked eye.

You can’t tell where a hairline fracture inside metal part is about to fail. But it can happen.

Here’s a sobering but powerful story from CampAddict about a potentially fatal towing mistake: Connecting your safety chains and breakaway switch cable directly to the hitch.

That’s something most people do without thinking about it (myself included!) But as the article shows, if the hitch itself every fails, then nothing works as it should. Your safety chains won’t matter, but they’re connected to the broken-off hitch! Your breakaway switch won’t engage, because the cable is tethered to the broken-off hitch!

The Solution: Math (Sorry, You Asked!)

If you don’t want to become Example #5, you need to do your own diligence.

Don’t listen to the RV dealership salesperson. He won’t be footing the bill if your truck breaks down.

Don’t worry – you don’t have to become an expert in RV towing physics and regulations! You can follow these three simple steps:

  1. Educate yourself! Read this blog and check out the towing calculators at Changing Gears.
  2. Get the numbers. Take your RV to a certified weigh scale, or even better, a wheel position weighing scale (research local RV rallies near you to find one). Learn EXACTLY how much your RV weighs when empty and when packed. Write down your tongue weight or king pin weights. Write down your actual wheel weights. Get it all down on paper!
  3. Do the math. I actually encourage you to work through the math yourself. It’s a great way to educate yourself, and soon, it’ll be second nature! It’s the only way to get 100 percent accurate results. But if you’re scared of arithmetic, again, I recommend checking out the educational calculators at Changing Gears.
  4. Retire old parts. I get it – if it ain’t broke, why fix it? But some parts, like safety chains, couplers and hitch pins, are fairly cheap to replace. After being in service for 10+ years, maybe it’s time to retire and replace. 
  5. Evangelize. Warn other RVers if you see warning signs that they’re towing dangerously or when overloaded. If we work together, everyone stays safe!

Ross

RV engineer by day, intrepid blogger by night (and occasionally weekends). This website is all about how RVs work, and sometimes why they don't. Bookmark pages that you find helpful, and join my email list for exclusive monthly awesomeness.