Trailer Towing

Today we are going to discuss a couple of confusing topics in the world of trailer towing, Understanding Tow Vehicle and Trailer Weights & Trailer Tongue Weight with a  Weight Distribution Hitch. That’s a mouthful.

My goal with this article is:

  • To explain these confusing topics in layman terms, so it is easier to understand.
  • To help you make a good choice when it comes to properly and safely matching a tow vehicle with a trailer, in regards to trailer tongue weight and towing.

With that said, I want to begin with some trailer towing basics. Trailer tongue weight is the amount of weight exerted straight down on the trailer’s hitch ball.  For trailers weighing more than 2,000 pounds, the recommended trailer tongue weight is 10 to 15 percent of the fully loaded trailer.

There are lots of variables that contribute to trailer sway, but perhaps most importantly is the trailer’s tongue weight. Imagine for a moment what happens when tongue weight is applied to a hitch ball. This added weight to the tow vehicle’s rear axle generates friction to the tow vehicle’s rear wheels. But too much tongue weight can affect the tow vehicle’s steering and handling, and too little tongue weight can result in a loss of traction, contributing to trailer sway.

So, it’s important to understand, if you are towing a loaded trailer with less than 10 percent tongue weight it can contribute to trailer sway because the tires lose friction on the road surface. On the other hand, a trailer with too much tongue weight, causes the front tires to lose friction which in turn affects the steering and handling. If the tongue weight (what generates friction to the tow vehicle’s rear tires) is properly distributed to all of the tires on the tow vehicle, most lateral forces you encounter will not be sufficient to start trailer sway. But if the lateral forces do overcome the tire friction, trailer sway can start. We’ll talk more about this topic later.

I won’t sugar coat this, because both of these situations are extremely dangerous to you the driver, your family members, and other travelers on the same road as you.

Now we can get to the good stuff

I mentioned a moment ago there are lots of variables that contribute to trailer sway, and the same applies to the trailer and tow vehicle weights too.

It’s important to understand when you select a tow vehicle you need to research all of the variables. For example: 

  • What brand vehicle is it?
  • What model is it?
  • What is the cab configuration?
  • If it’s a truck, what is the bed size?
  • What size engine does it have?
  • What transmission does it have?
  • Is it a 2WD or 4WD vehicle?
  • Does it have a towing package?
  • And possibly most importantly, what is the rear axle ratio?

Did you know there can be two trucks that are identical to each other except for the rear axle ratio, and the tow capacities can be thousands of pounds different.

Tip: If you use a towing guide pay particular attention to the footnotes. The footnotes will help guide you as to what vehicle configurations can tow what amounts of weight. And, don’t believe everything a salesperson tells you. Verify all of the vehicle’s information prior to purchasing the vehicle. The VIN number, labels posted on the vehicle and vehicle owner’s manuals are helpful in locating some of the information.

I’ll try to keep our towing example simple

Our truck is a Ram 1500 crew cab with a 5’7” bed and it is 2WD. It has a 5.7L hemi engine with an 8-speed automatic transmission. The rear axle is 3.92:1.

Here are the vehicle specs we need to look at

Gross Vehicle Weight Rating (GVWR) 6,900 pounds
Payload 1,840 pounds
Curb Weight 5,065 pounds
Base Weight Front 2,945 pounds
Base Weight Rear 2,119 pounds
Front Axle GVWR 3,700 pounds
Rear Axle GVWR 4,100 pounds
Gross Combined Weight Rating (GCWR) 17,000 pounds
Maximum Trailer Weight Rating (MTWR) 11,530 pounds

Note: All of these weights and weight ratings are important in properly matching a tow vehicle to a trailer. It is not safe to exceed any weight or weight rating.

This probably looks confusing now, but once we start adding things up it will make more sense.

One interesting note is: Ram states that Payload and the Trailer Weight Rating are mutually exclusive. Mutually exclusive means, of or relating to a situation involving two or more events, possibilities, in which the occurrence of one precludes the occurrence of the other. I will keep that in mind.

Payload is all of the weight placed in or on the vehicle. Payload is important, especially if the weight added on or in the vehicle causes it to exceed the Rear Axle Weight Rating (RAWR) or the vehicle’s Gross Vehicle Weight Rating (GVWR).

Note: This happens more often with a 5th wheel trailer, because the hitch or pin weight is directly over the tow vehicle’s rear axle.

So, what this tells us is, the more weight you put in or on the tow vehicle, the less you can tow. I’ll talk more about this in a minute. Payload = GVWR – Base or Curb Weight. So, in our example: 6,900 GVWR – 5,065 Curb Weight = 1,835 Payload.

Note: the weight of the hitch itself is included in the payload calculations.

If we add the base weight of the front and rear axles together, we get 5,065 pounds, which is the curb weight of our vehicle. And if we add the max payload of 1840-pounds, we get our GVWR of 6,900 pounds. Is it starting to make more sense now?

Note: Keep in mind this is a base model truck with no accessories or aftermarket equipment. So, you need to consider any aftermarket accessories like a spray in bed liner, running boards, tool box, or another fuel cell. To keep your numbers as precise as possible, the weight of all aftermarket accessories gets added to the vehicle’s empty curb weight figure and counts as payload.

Now let’s see how much our tow vehicle can tow

One of the most important weight ratings you need to understand, as it pertains to the tow vehicle, is the Gross Combined Weight Rating (GCWR). The GCWR is the maximum amount of weight the fully loaded tow vehicle and the fully loaded trailer can weigh when combined together. Keep in mind I said the fully loaded tow vehicle and trailer.

Our tow vehicle’s GCWR is 17,000 pounds. So, 17,000 – 5,065 Curb Weight = 11,935 Max Trailer Weight Rating. This is how the maximum trailer weight rating is usually figured to determine how much the tow vehicle can safely tow. Notice I said usually; in this particular example the vehicle manufacturer states in the towing guide, the maximum trailer weight rating this truck can tow is 11,530 pounds. So, for whatever reason, the vehicle manufacturer lowered the maximum trailer weight rating by 405 pounds. I’m not sure why.

This is where things start to get interesting

What we know so far is, our tow vehicle, with a full tank of fuel and driver can safely tow a trailer that does not exceed 11,530 pounds when fully loaded. If you recall, earlier I said any weight you put in or on the tow vehicle reduces the maximum trailer weight rating by that same amount. For the sake of this example, if we add an additional 50-gallon fuel tank in the tow vehicle (300 pounds), three passengers (400 pounds) and the hitch weight (100 pounds) the tow vehicle now weighs 5,865 pounds.

 5,065 Curb Weight + 400 pounds passengers + 300 pounds fuel + 100 pounds hitch weight = 5,865 pounds

Now take the vehicle’s GCWR of 17,000 pounds – the truck’s GVW 5,865 = 11,135-pound maximum trailer weight rating. But keep in mind the manufacturer lowered the max trailer rating by 405 pounds, so the maximum weight you can tow now is 10,730 pounds rather than 11,530 pounds.

So, in the real world you need to deduct all of the weight added in or on the tow vehicle, from the vehicles 17,000-pound GCWR (and don’t forget about the manufacturers 405-pound deduction).

Trailer Weights, Tongue Weight & Weight Distribution Hitches

So far I discussed everything having to do with the tow vehicle, now let’s talk about the travel trailer. When you look at a travel trailer’s weight, there is the empty or dry-weight and the Gross Vehicle Weight Rating (GVWR). The dry-weight is how much the trailer actually weighed based on what options the dealer added to the trailer when it was ordered and delivered. Any aftermarket products you add, like a deep-cycle battery, satellite dish, or solar panels etc., the weight gets added to the trailer’s dry-weight.

The GVWR is the maximum amount of weight that can be placed on the trailer’s axles. The difference between the trailer’s dry-weight and the published GVWR is the cargo carrying capacity, or the most amount of weight that can be added before it exceeds the GVWR.

For our example, let’s say the trailer we want has a dry-weight of 8,000 pounds, and a GVWR of 9,400 pounds. This means in a perfect world you could load 1,400 pounds to the trailer. But we already know the more weight added to the tow vehicle reduces the maximum trailer weight rating by that same amount of weight.

Another important consideration is the trailer’s tongue weight. In our example let’s say the published tongue weight of the trailer is 900 pounds. What this means is, with the trailer empty there is 7,100 pounds resting on the trailer’s axles, and 900 pounds resting on the trailer’s tongue jack. When you put the trailer’s coupler on the tow vehicle’s hitch ball the tow vehicle’s rear axle is now supporting the 900-pounds of tongue weight.

This is where things get a little tricky

When the tow vehicle is empty the rear axle has 2,119 pounds resting on it. Now, with the addition of 900 pounds of tongue weight, the rear axle has 3,019 pounds on it. So, there is 1,081 pounds left before the rear axle weight rating is exceeded. And this is without factoring in any payload that might get loaded in the back of the tow vehicle.

Chances are if you step back and look at the truck and trailer coupled together; the lowest point in the line is where the 900-pound tongue weight is resting on the hitch ball.

This is where a Weight Distribution Hitch (WDH) comes in

We want the 900-pounds of tongue weight, because that is a little over 11 percent of the trailer’s weight, but we don’t want  all of the weight resting on the rear axle of the truck. Remember when I said, too much tongue weight can cause poor steering and handling? A weight distributing hitch does exactly what it says, it distributes a percentage of the trailer’s tongue weight to the front axle of the tow vehicle, and a percentage of the weight to the axles on the trailer. This not only levels the trailer and tow vehicle (if installed correctly) it makes the trailer tow better too.

A WDH uses bars to leverage (or distribute) the weight placed on the hitch ball to the other axles in the towing system. In a perfect world, there would be 300 hundred pounds of tongue distributed to the front axle of the tow vehicle, 300 hundred pounds distributed to the trailer’s axles, and 300 hundred pounds remaining on hitch ball, or rear axle. But there is still 900 pounds of tongue weight. The only way to get real weight figures is to go to the scales and have it weighed.

Tip: It’s best to let a professional set-up and install the WDH. They need to take precise measurements, set the angle on the hitch head, and select the right size weight distribution bars for the trailer’s tongue weight.

Now, another wrench gets tossed into the mix

So far, we only talked about an empty trailer. Now we need to see how much the fully loaded trailer weighs, and how much of that weight is resting on the trailer’s tongue. Right now, if we don’t load anything else in or on the truck, we can tow a maximum of 10,730 pounds. Let’s say with the LP gas cylinders full, a half a tank of potable water in the fresh water holding tank, and all of the personal gear and cargo, the trailer weighs in at 9,100 pounds, an increase of 1,100 pounds overall. It’s possible for the trailer tongue weight to increase or decrease, depending on how the cargo weight is distributed throughout the trailer. In our example, we had about 11 percent of tongue weight based on the empty trailer. If you recall, the optimum tongue weight for a trailer is 10 to 15 percent of the fully loaded trailer’s weight. With a loaded weight of 9,100 pounds we could distribute some of the cargo weight towards the front of the trailer to help increase the tongue weight to roughly 12 or 13 percent of the loaded trailer weight.

And once again, you would need to head to the scales, or use a product like a Flash Integrated Scale Ball Mount or a Curt BetterWeigh Mobile Towing Scale to see what the adjusted tongue weight load is. Also keep in mind, unless you are using an Equalizer WDH with built in sway control, you will need to add some type of sway control device to the trailer. A typical WDH does not prevent or react to trailer sway. For more information: Understanding & Controlling Trailer Sway Article 

So in our trailer towing example, with the fully loaded trailer, we are still under the trailer’s GVWR of 9,400-pounds, and when you add the combined weight of the fully loaded trailer and fully loaded tow vehicle together we are well under the 17,000 pound GCWR for our vehicle. 5,865 GTW + 9,100 = 14, 965 pounds. 17,000 – 14,965 = 2,035 pounds to spare.

Keep in mind, this is merely an example. In the real world you would most likely add more weight to the tow vehicle, and you need to consider the terrain you might travel in, and the weather conditions. But, all in all this would be a properly matched tow vehicle and trailer.

Takeaway

What you need to takeaway from this article is, everything in a towing system (tow vehicle, hitch components & trailer) has weight ratings, and the GVWR must be calculated based on the weakest link in the towing chain. This can be the tires, the brakes, the axles or any other component used to construct the tow vehicle or trailer. One fairly common problem is overloading an individual tire. You might be within the trailer axle weight rating, but because of the way weight is distributed you can still overload a tire. The only way to properly weigh a trailer is by individual tire positions, tongue weight and axle weights. But this is hard to do. If you attend large RV rallies, it’s possible they might offer a weighing services capable of weighing by individual tire positions. But at the end of the day, any effort you make to weigh your towing combination, the safer you will be.

For more information on trailer towing, check out our Tow your Travel Trailer like a Pro Video Training Program

For more information on towing a 5th wheel, check out our Tow your 5th Wheel Like a Pro Video Training Program

For more information on trailer sway read my article Understanding and Controlling Trailer Sway

Happy & Safe Towing

Mark J.Polk

RV Online Training

RV Education 101

3 thoughts on “Trailer Towing

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s