RV engineer answers: Is maximum towing capacity just smoke and mirrors?

You will almost never tow what you think you can. To those of you who have owned RVs for years, this isn’t breaking news. Some of you follow the 80% Rule of Thumb: Your “real-life” towing capacity is around 80% of the advertised maximum. But is that margin even sufficient?

Let’s get into the nitty-gritty. And if you remember nothing else, remember this: Payload capacity, not towing capacity, is the real limitation of your tow vehicle!

Getting an answer about towing capacity is really, really hard!

I’m an RV design engineer. That’s right—I design some of the RVs you all are towing right now! And while I love this industry, I agree with the thousands of customers who demand better service, better construction, and better quality control. And nowhere is that information gap more excruciating than when answering the question, “How much can I actually tow?”

In recent years, the National Highway Traffic Safety Administration (NHTSA) has revised several labeling requirements to make towing and cargo capacities less opaque. But most customers still have trouble swallowing the alphabet soup—and RV salespeople aren’t exactly handing out calculators!

So I’ll say it again:

Payload capacity and hitch weight—not advertised towing capacity—will usually limit what you can tow.

• The cargo you add to your tow vehicle will drastically reduce what you can tow. In fact, with a full family and suitcases, you might not be able to tow anything!
• Real-life tongue weights can easily slash your towing capacity by 20-50% compared to the advertised maximum.

It’s bad news, I know. And while the 80% margin rule is useful, it’s still woefully inadequate. But I’d rather you find out now than $50,000 later.

Can you even trust advertised towing capacities?

The advertised towing capacities of most consumer pickup trucks are governed by the SAE J2807 standard—

Hey, don’t doze off! Get back here!

Motor Trend shows how the SAE J2807 is actually a pretty amazing test. The Highway Gradeability test takes place on the 11.4-mile Davis Dam road, a nasty hill climb in the Arizona sandstone desert, where the outside temperature must be 100 degrees minimum. It’s literally hell on wheels. I have a hard copy at my desk, so I can promise you it’s serious business!

So towing capacities are (mostly) standardized across manufacturers. Vehicles must survive several eye-popping strength and endurance tests. So that’s the good news. You can reasonably trust that you’re comparing apples to apples, Ford to Chevy.

But … can that Ford F-250 really tow 20,000 lbs.? Like, really?

When it comes to towing, the devil’s in the details

Auto manufacturers have dreams about the coveted status of “best towing capacity in class!” They’ll squeeze every pound possible out of their pickups (and their brochures). Their job depends on it.

So yes, some half-ton pickup trucks can tow 13,000 lbs.—with the right engine, axle ratio, bed length, cab style, hitch, tires, towing package, tongue weight, and a full harvest moon.

That’s a lot of assumptions. Here are some of the calculation assumptions typically made. (Check your manufacturer’s Towing & Trailering guide for the most up-to-date information.)

• Tow vehicle includes a 150-lb. driver and a 150-lb. passenger. (I don’t know about you, but I haven’t been 150 pounds since I was 16!)
• Tow vehicle includes the factory-installed heavy-duty towing package.
• No driving at high altitudes.
• No cargo besides operating fluids.
• No dealer-installed options or accessories.
• RV is towed with a weight-distribution hitch, not a weight-carrying hitch.
• RV has minimum allowable tongue weight (usually 10% for travel trailer or 15% for 5th wheel).

If any of those are not true … then you won’t be able to tow the maximum towing capacity. And in all my life, I’ve never met anyone who towed with a perfectly balanced hitch, no kids, no cargo, and no accessories! What a boring vacation that would be!

Let’s see how these real-life constraints change the maximum towing capacity for an RV.

P.S. You can find your advertised towing capacity on a Trailering Guide or Towing Selector chart from your manufacturer. You can also subtract your tow vehicle’s GVWR from its GCWR, both of which you can find on your Safety Compliance Certification Label.

What difference will just one pound of cargo make?

Adding cargo to your tow vehicle will multiplicatively reduce its towing capacity.

^That’s a super important sentence, so I recommend you read it again. You may not think that 90 pounds of cargo is a big deal. I mean, that’s just a large dog, right?

Let’s see what happens if you bring Fido along.

If your advertised maximum conventional towing capacity is 13,000 lbs., then I’d wager my retirement account (not worth much these days) that the auto manufacturer is assuming 10% tongue weight and a weight-distribution hitch.

If Fido is sitting in the middle rear seat, let’s assume half his weight (45 lbs.) is on the rear axle.

Now, the physics of weight-distribution hitches (WDH) can get complicated, so we’ll skip the algebra. But if your WDH is set up with ~66% FALR (front axle load restoration), then roughly 1 lb. gained on the rear axle = 12 lbs. loss of towing capacity. (That’s a super rough estimate, but it makes the numbers easy.)

Translation: If we assume half the cargo weight is on the rear axle, then every 1 lb. of cargo = 6 lbs. loss of towing capacity. At a certain threshold, it shuts down towing capacity completely.

So 90-lb. Fido just removed 540 lb.s of towing capacity. (Bad dog!)

And once you add your two 50-lb. suitcases and another 100 lbs. of emergency tools, snacks, drinks, and fishing gear, you’ve lost another 1,200 lbs.! Oof.

Note that you’re still well underneath your GCWR. But that doesn’t matter. You can’t overload your tow vehicle’s rear axle—and that’s what usually gives way first with heavy towable campers!

What difference will just 1% of tongue weight make?

Again, I’ll eat my hat if the auto manufacturer isn’t assuming 10% tongue weight for travel trailers (or 15% for 5th wheels). So a “13,000-lb. towing capacity” is just another way of saying a 1,300-lb. maximum hitch weight.

So, what if your travel trailer actually has a 13.5% tongue weight? (Which is a very reasonable number within the usual 10-15% range).

Turns out, that’s an extra 455 lbs. on the hitch. Not good. And because tongue weight multiplies weight on the rear axle, you’ve probably overloaded your rear axle by even more, up to 500-700 lbs.

Yikes. So with a 13,000-lb. trailer, you’ve way, way overloaded your rear axle and tires. You’re risking tire blowouts and permanent suspension damage.

Once you crunch the numbers … with a 13.5% tongue weight, you could only tow 9,630 lbs., tops. Not 13,000. That’s 3,370 lbs. less than you thought!

(And we haven’t even added Fido yet.)

This is also why very few half-ton pickup trucks can reasonably tow a 5th wheel camper. The pin weight is just too much for the rear axle, especially once you climb above 15%!

So what’s a math-averse RV owner to do about towing capacity for RVs?

Hey, it’s not all bad news! You have options.

• Weigh your RV. You don’t have to crunch numbers. You can take your RV to a scale and have all your axles weighed. Then adjust payload from there.
• Use a calculator. Check out this Travel Trailer Towing Calculator or this 5th Wheel Towing Calculator. While no calculator is 100% accurate, they can point you in the right direction.
• Research before you buy. I’ve talked with a lot of RV owners who discovered too late that they couldn’t realistically tow their new $75,000 RV. They either had to buy a new $50,000 truck or sit on a $75,000 white elephant. Researching tongue weights, pin weights, and payload capacities should be de rigueur for any RV purchase!
• Go smaller. I know it’s anti-American, but smaller RVs are the future. You can venture off the pavement, store them in your backyard, and tow them with half-ton trucks. Better to keep your tow vehicle big and your camper small.

I should answer one last question: Is the 80% Towing Margin rule safe?

Eh … it’s inaccurate. For big families and packrats, a 60-70% margin is more practical. But as I warned earlier, if you load up a Chevy Suburban with seven husky people and seven suitcases, you’ll probably max out the GVWR—and you won’t be approved to tow a single pound!

##RVT1076