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RV Tech Q&A: August 2020

Originally Published in Trailer Life Magazine

Tow-Rig Payload Capacity


I quite enjoy the annual Guide to Towing information. It’s very helpful for a newbie. We recently upsized from a 2015 2500 Ram diesel Crew Cab shortbed with single rear wheels to a 2019 Ram diesel 3500 with a greater gross vehicle weight rating (gvwr) than the 2015 model. What I found missing in the guide was vertical tow weight rating (vtwr). I am curious how this would be calculated. I see some dealers identify the “payload” capacity; I am wondering if this is the same as the vtwr.

Can you please provide some perspective?
Owen Konski | Fort McMurray, Alberta


What you refer to as vertical tow weight rating, Owen, is usually known as payload capacity. This figure is determined by starting with the truck’s gvwr and deducting its curb weight. The difference is how much weight can be added before exceeding the truck’s gvwr. For example, a truck with a 10,000-pound gvwr that weighs 8,200 pounds will have an 1,800-pound payload capacity. That figure would be reduced by adding passengers and a bunch of cargo, depending on how the curb weight was measured.

As for how much weight the truck can handle in its bed, with the weight focused on the rear axle, that calls for knowing the truck’s gross axle weight rating (gawr) for the rear axle, as well as the truck’s rear-axle curb weight. For example, if the truck has a 7,000-pound-rated rear axle and actual weight is 4,500 pounds, that leaves a 2,500-pound payload capacity.

These are just example figures and do not relate directly to the above circumstances. However, don’t be surprised if the front- and rear-axle capacities add up to more than the truck’s overall payload capacity.

The gvwr is based on many factors, front- and rear-axle weight-carrying capacities among them, as well as engine power and drivetrain components, engine cooling, vehicle braking and steering components. Be aware of all the weight calculations, and you can avoid overloading, be it on the rear axle or the entire truck.

The best way to make these calculations, if you’re shopping for a truck and have one in mind, is to take it to a public scale, like a CAT scale at a truck stop, and record its weights. To be consistent, start with a full fuel tank, stay in the cab and have the salesperson stay there, too. Record its overall weight, plus its individual front- and rear-axle weights.

You can find the gvwr and other figures on the vehicle sticker on the driver’s-side doorjamb. Using this information, you can determine the real-world payload capacities for a truck. Be aware that any weight you add to the truck, such as a fifth-wheel hitch, heavy tools or supplies, will alter those calculations.

Weighing In

This is in regard to “Truck for Slide-In Camper,” Greg Buntain’s June RV Clinic letter. Your reply gives the correct solution to the problem with the Chevy 3500 series, but I have not heard an explanation about why the 2500 series doesn’t work for serious payload. The problem is cited frequently, but no one, including writers such as yourselves and truck dealer staff, talks about why. You will do all RV buyers a great service if this simple fact is addressed. I learned the hard way myself.
A 2500 gas engine has about a 3,000-pound payload and does the job. If you decide on a diesel engine, which comes with an associated transmission, this reduces the payload capacity by about 1,000 pounds due to the increased weight of the diesel engine and transmission. Therefore, RV and slide-in-camper buyers who want a diesel engine and payload should always go with the 3500 series, which has the real 3,000-pound or more payload capacity.
Steve Brunow | North Dinwiddie, Virginia

Steve, you’re right. The diesel is heavier, and thus reduces the payload capacity. However, diesel towing capacity far exceeds the gas engine, in either three-quarter or one-ton versions. This is especially a concern with fifth-wheels and truck campers where there is so much vertical loading of the truck.
Single-rear-wheel trucks have a lot more capability now than in years past, especially when it comes to towing capacity. But just because a truck has a super high tow rating doesn’t mean it has a matching payload capacity. Each manufacturer has a detailed guide for tow ratings and payload, and those should be looked at carefully before matching a truck to a trailer.
Also, it’s not just the powertrain that can reduce payload; consider the cab size, bed size, wheelbase and option packages. A 3500/350 truck still may not be able to handle the weight.

Mouse-Free Hitch

I have a 2010 35-foot Heartland Bighorn. I am considering having a trailer hitch put on it, but I’m concerned about the integrity of the underbelly material. I know that the material would have to be cut for the hitch to be welded to the frame. What do I need to know when dealing with the installer of the hitch? Right now, I don’t have any problem with critters getting into the trailer, but I worry about what happens after the material is cut.
Rod Breheim | Lino Lakes, Minnesota

We understand where you’re coming from, Rod. Mice can wreck RVs! The good news is that it’s pretty simple to reseal the underbelly after the hitch is installed. If it’s never been opened, the underbelly is likely held on with washer nails that are pneumatically installed at the factory. Those need to be pried out to release the material.
Once the hitch is installed, the coroplast should be carefully trimmed just enough to allow for the hitch. Resecure the coroplast with self-drilling TEK screws with washers. Any gaps should be filled with expanding-foam insulation. Once that has cured, a can of gloss-black Rust-Oleum can be used to dress it up. That should deter rodent intrusion.

Have a Tech Question?

Email [email protected] and include your full name and hometown. Selected letters will be answered in the monthly RV Clinic column, but time does not permit individual replies.

Jeff Johnston served as technical director of Trailer Life for 20 years and has been an RV enthusiast, mechanic and writer since he could hold a wrench. In his monthly RV Clinic column, Jeff replies to Trailer Life readers’ technical questions about RVs and tow vehicles. He also serves as associate producer of Rollin’ On TV, a nationally syndicated television program for RV enthusiasts.


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