So you have found yourself in the situation of having a vehicle and wanting to know what it can tow, or having a trailer and wanting to know what to get to tow it. There are a lot of factors that go into this grand calculation, so let’s see if we can work through things. A bit of advice right off of the bat: We all love our car dealers, but in all honesty, they will say whatever they need to get you to buy that truck. So if you ask them, ‘Can this tow my trailer?’, they will almost always say yes. Don’t trust what they say, just get the paperwork and documentation on the vehicle you are looking at from them. What I have written here is fairly condensed and hopefully in plain language. For a more in depth read with a lot more information, especially on specific vehicles, I recommend reading Trailer Life towing guides. After clicking on the link, you can navigate to a pdf of the year you are looking at, and get some more specific information.
First off, let us cover some terminology that gets tossed around and flies over peoples heads.
Gross Combined Weight Rating (GCWR) – This is the biggie number. This is the total weight that you can move, including tow vehicle, trailer, passengers, any and all cargo, and any fluids (fuel, water, and anything you have put in the black tank).
Gross Vehicle Weight Rating (GVWR) – This is the total weight for your tow vehicle. This number includes all passengers and cargo in your tow vehicle and the tongue weight of the trailer. This rating is for anything you are putting on the tow vehicles axles.
Gross Axle Weight Rating (GAWR) – This is the total weight that can be applied to an individual axle. This will include the tires, brakes, and axle itself. Note that most trucks should have a higher rating for the rear axle.
Maximum Tow Rating – The manufacturer will give a limit for a towed load. The caution to this is that they are not accounting for all of the weight in the tow vehicle that someone will put in it (i.e. just the driver and no passengers). Usually they will give a different number for a bumper pull trailer versus a fifth wheel.
The trailer will have two different weight ratings. One will be the total trailer weight, or Gross Trailer Weight Rating. The other will be the rating that the axles can handle. The GTWR will be the higher of the two numbers, since part of the trailer weight will be on the hitch. For a bumper pull, this could be up to 10% of the trailers total weight, and on a fifth wheel, it could be up to 20% of the trailers weight.
Very few trucks are created the same, even from the same manufacturer and model year. There are a lot of truck options that affect what the tow rating will be, and here are many of those variables.
Engine and transmission. These are a no brainer, and will be consistent between models of the same year, but from year to year, and especially diesel or gasoline, will affect the rating. My personal opinion is that you should always get a diesel. They have more power and a higher pulling capacity, plus they last a lot longer. Worth the extra expense in my book.
Wheel base. How far apart the front and rear tires are will affect the tow rating. A shorter span means less stability, while a longer span increases the stability. Something to consider before getting that regular cab short bed. As a note, the bed of the truck does not affect tow rating (outside of the different wheel base). A long bed truck does put the pin farther back from the cab, thus keeping the swing of the trailer nose away from the cab of the truck. A short bed pickup may necessitate the use of a slider hitch, but that is a different conversation.
Rear axle. We mentioned this above, but it plays into how much payload can be put on the rear of the truck.
Suspension. More and heavier duty springs/leafs mean that more weight can be put on the back of the vehicle. Some people (myself included) will put after market air bags as a supplement or replacement for the rear suspension. The set I put on is rated for 5,000 pounds per bag.
Rear differential. This is what those guys are talking about when they day “I have a 3.73 on the back”, or, “Man I wish I had gotten the 4.10”. Often, they will say it like ‘Four-Ten’. This number is part of a ratio, and that is where the drive shaft from the transmission connects to the rear axle. This is what makes your vehicle go. As a refresher from our introduction to physics class, the higher the ratio, the more mechanical advantage. So, a truck with a 3.31 will have less MA than a truck with a 4.10. The better the ratio, the more pulling power, the higher the tow rating. The flip side to this, and this is where people have a balancing act, is that the higher ratios mean that the engine has to turn faster to get to the same speed compared to a smaller ratio, which means less fuel economy. For example, a truck with a 3.31 may be able to do 70 mph at 1600 rpm on the tachometer, while a truck with a 3.73 may have to run its tachometer at nearly 3000 rpm to achieve the same speed (obviously transmission and gearing comes into play here as well).Single rear wheel (SRW) or dual rear wheel (DRW). More tires on the back means more weight can be applied. A DRW truck is also referred to as a dually, or as the daughter from Promised Land said, ‘It has hips.’ Now you have your tow vehicle and trailer. It’s time to load things up and get ready to head out. Can you just put all of your stuff where ever you want? Not really. Now it is time to address weight distribution. You have anywhere from 3-5 axles between your tow vehicle and trailer. Each axle is designed to carry a maximum amount of weight. Here is the point where you need to balance out the weight, so that no axle is carrying more than it should. The first thing to look for, and theoretically the easiest to adjust, is to make sure that your tow vehicle and trailer are level.
With both frames level to the ground and parallel to each other, each axle is bearing its own weight. In the top example, the rear tires of the tow vehicle are bearing more weight than the front, and the trailer has more weight bearing on its front tires as opposed to the rear. This type of condition affects the axles, tires, steering, and braking. The bottom example is corrected using a weight distributing hitch, but shifting cargo does come into play. Each tow vehicle is rating for a maximum tongue or hitch weight, so if you are over on that weight you will need to shift come cargo away from the front of the trailer.
On a fifth wheel trailer, the hitch inside the bed of the truck will have some height adjustment. On some hitches this is accomplished by removing some bolts and adjusting the hitch up or down to new bolt holes.
As a note, you will not want to check level with an empty trailer. Put all of your cargo in the trailer first before adjusting level, because the added weight will compress the suspension on the tow vehicle.
Weighing your tow vehicle and trailer.
So now that you have everything loaded up, how do you figure out your weight? Easiest answer is head to the nearest truck stop and use the scales there. The most popular is CAT Scales, and I have found them at most truck stops. There is a charge, but in the long run this $10 (price can vary) can save you a lot of headache and unnecessary expense. It may seem intimidating at first, but don’t worry and follow this process.
- Park and head inside to the counter. Let them know that you would like to weigh your RV/trailer and that it is a private sale. You or the person at the counter may arbitrarily assign a number to the transaction. This is so that the employee can keep track of the weighs in case others are weighing as well.
- If this is your first weigh, you will need to do several weighs. You can let the employee know that you will be doing a few re-weighs (for trucks, this is for when they need to shift some cargo around to balance the weight on each axle). There is an additional charge, but it is at a reduced rate.
- For your first weigh, you are looking for several numbers to make sure that you are within all of your vehicle and trailer ratings.
- You will need to get a weigh of your tow vehicle and trailer connected. Example is from the CAT Scales website. Click the link for more examples.
- You will need to get a weigh of just your tow vehicle.
- From the above illustration, you can see that there are actually 3 separate scales that your setup is sitting on. When you get your print out, there will be a gross weight line, a steering axle line, a drive axle line, and a trailer axle line. With these four numbers, plus the individual weigh of your tow vehicle, we can do some math and figure out all of our weights.
- Immediately, you have your GCWR to know if you have exceeded your tow vehicles rating. This is the grand total on the first weigh from above.
- If you take your GCWR and subtract your tow vehicle weigh (the total from that ticket), you get your Gross Trailer Weight. This is the weight that your trailer frame is rated for.
- If you take the drive axle weighs (block 2 in the diagram) and subtract one from the other, you get your pin weight.
- Each weigh will give you the steering axle weight.
- Block three from the first weigh will give you your total trailer axle weight. If you have a multi-axle trailer, you can do a third weigh and split the axles between block 2 and 3 to get a weigh for each axle to see if they are equally loaded.
- Some notes to consider before you weigh.
- Fill up your tanks before you weigh. You want to weigh in the most loaded up conditions possible. This includes your fuel tank(s), any transfer tanks, and if you plan on carrying water for boon docking.
- Have all of your passengers in the vehicle. Including your pets.
- At the scale, there is a ‘squawk box’. This is how you communicate with the employee inside. It is designed for a semi truck to use, which means it is high off of the ground. Be prepared to lean way out of your window or have a stick to reach the button.
- After your weigh(s), head inside to pick up your tickets.
Any subsequent time you weigh, you only need to do the combined weigh and note any differences.
The above weighing only covers load distribution from front to back on the axles. Unfortunately, the scales are not designed to let you only take one side of your vehicle onto them to get a side to side distribution. For this part, it is up to your discretion to make sure that your vehicle and trailer are balanced side to side. If you notice either one leaning to one side, you may need to redistribute some weight.
I hope that this has been helpful and answered your questions. Feel free to comment or email me with any other questions that I may not have addressed. Safe travels!