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Matching Your Tow Vehicle & RV Trailer

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FOR    YOUR    SAFETY
Matching a Tow Vehicle and Recreation Vehicle Trailer
By John Anderson, Executive Director of the RV Safety Education Foundation

How much can a customer tow? What tow vehicle does my customer need for their trailer?

These are common questions that require honest, factual answers, as SAFETY is at stake! Although a subject that evokes much speculation and a plethora of opinions (frequently wrong), the answer is quite simple if we assume that the desired outcome is to operate the rig in compliance with the manufacturers' limitations. Before we start, we need to understand a few definitions:

GVWR: Gross Vehicle Weight Rating: the maximum permissible weight of the vehicle when loaded for travel.
GAWR: Gross Axle Weight Rating: the maximum permissible load on an axle. The GAWR is based on the assumption that the load is equal on both sides.
GCWR: Gross Combined Weight Rating: the maximum weight of a combination of vehicles, i.e., a tow vehicle and trailer(s). GCWR assumes that the trailer has functioning brakes.
MLTW: Maximum Loaded Trailer Weight: The maximum weight that a tow vehicle is rated to tow. Hitch Ratings: The hitch on a tow vehicle will have two distinct and important ratings. The TOW rating, which defines the maximum weight of a trailer in tow. The VERTICAL or TONGUE rating, which defines the maximum vertical hitch load that the trailer can impart to the tow vehicle.


With these terms understood, let's use a few examples and see how we determine the correct match.

Example 1: We have a trailer, and we want to determine what tow vehicle we need.

All RV trailers have a data plate attached by the manufacturer that supplies the information that we need, located somewhere on the left front corner of the trailer, either on the body or on the hitch/tongue. It is here that we find the GVWR. We MUST ASSUME that we will load the trailer to GVWR! RVSEF has weighed more than 15,000 RVs since 1993, and the majority are loaded to GVWR and over!
With the GVWR in hand, we need the tow vehicle manufacturer's specifications. These are found in the Towing Guide published by each tow vehicle manufacturer. Here we will find the two critical numbers that we need to ensure safe towing; Maximum Loaded Trailer Weight and GCWR.

You will note that Towing Guides do not indicate how much a vehicle can PULL! Pulling is only one of several factors that must be considered when towing. Stopping is critically important. The relationship between tow vehicle weight and trailer weight is important, as too much trailer will have the "tail wagging the dog." Tow vehicle manufacturers consider all of these and more when they establish ratings.
To determine the maximum loaded trailer weight from the Towing Guide, you will simply enter the chart at the GVWR of the trailer, and follow the table to the required tow vehicle. The Towing Guide will define what size truck is required, and how it must be equipped, i.e., engine, rear axle ratio, body style, etc.
But we are not done! The Towing Guide will also define the GCWR. If we want to assume worst case, we simply add the GVWR of the tow vehicle to the GVWR of the trailer, and ensure that we select a tow vehicle rated for this combined weight. If the selected tow vehicle is a? ton truck or passenger car, its GVWR should be used. However, many tow vehicles are not loaded to GVWR by the owner, in particular, those towing trailers with ? and 1 ton pick-up trucks. In this case, it will be necessary to calculate the weight of the truck when equipped and loaded for towing.
The empty weight of the truck can be obtained from the truck dealer. To this, we need to add the weight of any accessories including the hitch, a full load of fuel, the weight of passengers, and the weight of any cargo. Now we add this calculated tow vehicle weight to the GVWR of the trailer, and ensure that it does not exceed the GCWR of the selected tow vehicle.

Example 2: We have our tow vehicle and we want to know how much trailer we can tow.

This process is essentially the reverse of the above example. Referring to the Towing Guide of the tow vehicle, and using the truck specifications indicated (engine, rear axle ratio, etc.), we simply follow the table and determine the maximum loaded trailer weight. The trailer we select must not have a GVWR greater than this number!

Since we have the tow vehicle, we do not have to calculate its weight to determine compliance with GCWR. Simply take it to a scale, loaded for towing, including passengers. Add this weight to the GVWR of the trailer, and compare the total to the GCWR of the tow vehicle. The total weight must not exceed GCWR!

Hitch Loading

Selection and proper installation of a hitch that is rated properly is an essential part of matching a tow vehicle and trailer. The hitch must have a tow rating at least equal to the GVWR of the trailer. The vertical rating of the hitch must be at least equal to the vertical load imparted by the trailer to the tow vehicle.

Verification

In our two examples we have analyzed the weight of the two vehicles to ensure that we operate within all limitations. For most cases, if we adhere to the limitations, we will not encounter other issues such as exceeding tire and axle ratings of the tow vehicle. However, it is important to verify the safety of the rig after it is set up and fully loaded for travel. To do this, we take the rig to a truck scale and measure the load on each axle of the tow vehicle, and the total load of the trailer axles. (If possible, individual axle loading on the trailer should be obtained, but this is not practical on many truck scales.)
After weighing the rig, disconnect the trailer and take the tow vehicle back to the scales and get another set of axle loads. Now we can calculate the loading of both vehicles and the hitch to ensure that all limitations are respected. First, add the axle loads obtained from weighing the total rig. This will give you're the Gross Combined Weight, which must not exceed the GCWR of the tow vehicle.
Next, add just the axle loads of the tow vehicle when the trailer was attached. This will give you the Gross Weight of the tow vehicle, which must not exceed its GVWR.
Now, add the axle loads of the tow vehicle when the trailer was not attached, and subtract this number from the axle loads of the tow vehicle when the trailer was attached. This will give you the vertical load imparted by the trailer to the tow vehicle, which must not exceed the vertical rating of the hitch.
Finally, add the total load of the trailer axles to the vertical hitch load calculated in the above step. This will give you the Gross Vehicle Weight of the trailer, which must not exceed its GVWR, and ALSO, must not exceed the tow rating of the hitch.
As a final verification of safety, compare the axle loads obtained above to the GAWR posted on the data plates. The Gross Axle Weight must not exceed its GAWR.
We have not addressed tire loading and inflation here, as it is another subject unto itself To ensure optimum tire life and performance, tire loads must be individually measured on each vehicle, and the results compared to the tire manufacturer's specifications. This process will reveal the correct inflation pressure for the tires, and verify that the correct tire is being used for the application.

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John Anderson is the Executive Director of the RV Safety Education Foundation, a non-profit corporation dedicated to providing the RV industry with accurate, positive, industry approved information. Information about RVSEF is available on its web site at http://www.rvsafety.org Questions on this subject and other RV safety education related matters are welcome. John can be reached at john.anderson@rvsafety.org , or (423) 257-4940. Tax-deductible contributions to RVSEF are encouraged, and contributors are recognized both on the web site and at the RV rallies shown on the web site Seminar Schedule.


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