Choosing a Tow Vehicle - Part I
Choosing a tow vehicle for your trailer is a complex process, the goal of this post is to make it as simple as possible without skipping over the critical details. Anyone looking for a tow vehicle (or looking for a trailer for their existing tow vehicle) should find the information useful. We also go into the factors that informed our tow vehicle choice for our Airstream (spoiler alert: We decided on a 2014 Chevy Silverado 1500 EcoTec3 5.3L V8 4WD) in Part II.
Caveat: I do not have an advanced degree in towing or tow ratings or tow vehicles, so please do not take this as the final word, but rather as a good starting point. I did spend an inordinate amount of time researching this stuff, and have put together the most salient points for your current benefit (and my future benefit, when I forget most of it as I inevitably will!).
Tow Ratings and Towing Capabilities
Before we start, it is important to get some definitions and math out of the way. The single most important factor in choosing a tow vehicle is that it can safely and reliably tow your trailer. In order to do this, we have to talk about weight ratings and towing capacity. Keep in mind that truck dealers and RV dealers are usually more interested in making a sale, and less interested in whether your tow vehicle/trailer combination is safe. It is always best to do the research yourself beforehand, rather than to rely on the dealer providing accurate information. Even if they do not try to intentionally mislead you, they may simply not know enough to help you make a good decision. Also just because you can tow a trailer with a specific tow vehicle doesn't necessarily mean you should. It is best to plan for the worst case (a loaded pickup and trailer up and down mountains) rather than the best case (an unloaded trailer, flat roads, no wind, etc.). Usually those who try and cut corners own a tow vehicle already and want to justify a larger trailer.
We do not talk about hitches in this post (perhaps in a future post), but they also play an important role in safely towing your trailer. In our opinion, a hitch that has anti-sway control is a must, and one that has weight distribution is also very useful especially for smaller tow vehicles.
There are several important weight ratings that you need to pay attention to. These ratings are all maximums - the most weight you can carry/pull/etc - your truck will usually perform better when the actual weights are lower. These ratings can be found in the owner's manuals and brochures for the specific tow vehicles and trailers. We also provide the ratings for our tow vehicle and trailer below.
On the tow vehicle (most commonly a half-ton or larger truck):
GVWR – Gross Vehicle Weight Rating. This is the maximum weight of the tow vehicle and cargo (includes passengers and fuel). Often this value is displayed on a sticker inside the tow vehicle.
GCWR – Gross Combined Weight Rating. This is essentially the GVWR plus (or combined) with the maximum weight of the trailer and the trailer's cargo.
Towing Capacity – The maximum weight of the trailer (including the trailer's cargo) that the tow vehicle can tow. This is the most important number for your tow vehicle. While you might assume this should be GCWR – GVWR, in practice the towing capacity is actually a little higher (there are some reasons for this, but they are rather technical so I will skip over them).
GAWR – The gross axle weight rating. This is the maximum weight that can be placed on an axle (this includes the truck/engine/frame/etc., not just the cargo). There is one rating for the front axle, and another rating for the rear axle. These are usually different, and the rear axle GAWR is usually higher on trucks. Note that the front axle GAWR plus rear axle GAWR is usually slightly higher than the GVWR of the tow vehicle. Neither of the three ratings should be exceeded.
Payload – How much cargo weight the truck can support. This does not include fuel (in other words, this number assumes you have a full fuel tank). Passengers and cargo are counted against the payload.
On the trailer:
GVWR – Gross Vehicle Weight Rating. Like the tow vehicle GVWR, this is the maximum weight of the trailer plus its cargo, including full holding (water/gray/black) tanks. Keep in mind that a gallon of water weighs 8.3 lbs. On our 25 FB Airstream our combined three tank capacity is about 120 gallons or 996 lbs. (though we rarely travel with all tanks full, usually a full gray tank means a mostly empty fresh water tank and our black tank is rarely full).
Base Weight (or Dry Weight): This is the weight of the trailer without any cargo and with empty holding tanks. This is used to give you an idea of how much cargo you can fit into your trailer before you reach the GVWR (GVWR - Base Weight - full holding tanks = approximately how much stuff you can put in your trailer).
Tongue Weight: This is the weight of the front part of the trailer, and it counts directly against the payload of the tow vehicle. Usually it’s about 10-15% of the GVWR of the trailer. Without a weight distribution hitch, the tongue weight will be on the rear axle of the tow vehicle, with a weight distribution hitch that weight will be spread among all axles of the tow vehicle and trailer. Weight distribution hitches are often critical for smaller tow vehicles. There is some controversy over whether using a weight distribution hitch (which actually distributes some weight back to the axle of the trailer) will give you back a little payload. In my opinion, it's safer to assume that it does not, and that the tongue weight, regardless of whether you use the weight distribution hitch, will always count fully against the payload. It's better to err on the side of having too much capacity than too little.
Making sense of the weight ratings
Now that we have the definitions out of the way, here is what you need to know to be safe:
- The towing capacity of your tow vehicle must be greater than the trailer GVWR (the max weight of the trailer fully loaded). While technically they can be equal and still be “up to code”, it is better to have a buffer on your tow vehicle (20% is a number we see often, we have a buffer of about 50%). Also if you are on the fence about what size trailer you want, having extra capacity on your tow vehicle means you might be able to get a larger trailer without having to get a new tow vehicle.
- The tongue weight of the trailer counts against the payload of the truck. The weight of your hitch also counts against the payload of the truck (some hitches do not weigh that much, our ProPride Hitch is pretty hefty at 195 lbs.). Even if you have enough towing capacity on your tow vehicle to tow your trailer, your available remaining payload can be decreased significantly. If you plan on carrying a lot of cargo (kids, dogs, a heavy generator, bikes, tools, etc.) this could become a factor.
- The tongue weight (plus the weight of your hitch) by default will be on the rear axle of your tow vehicle, and you may exceed the rear axles GAWR. We have a weight-distributing hitch so that this weight is spread among the axles of the tow vehicle and trailer.
To only way to accurately measure the weight of your trailer (full or empty), tow vehicle (full or empty), and axle weights is to use a scale (such as a CAT Scale which are located across the US). This will also help you calibrate your weight distribution hitch more accurately than using the time-honored “eyeball” method.
Example Weight Ratings
Here are some real-world examples of these ratings using our tow vehicle and trailer to give you a better feel for these ratings. You can find these ratings in the brochures or websites for your trailer and tow vehicles.
Our tow vehicle (2014 Chevy Silverado 1500 V8 4WD with max-trailering package):
GVWR: 7,200 lbs. (max weight of truck plus cargo plus passengers plus fuel)
GCWR: 16,700 lbs. (GVWR plus max weight of the trailer and the trailer cargo)
Towing Capacity: 11,200 lbs. (max weight of the trailer and the trailer cargo, notice this is higher than the GCWR - GVWR of 9,500 lbs.)
GAWR front axle: 3,950 lbs. (max weight on the front axle)
GAWR rear axle: 4,100 lbs. (max weight on the rear axle)
Payload: 1,866 lbs. (the max weight of cargo that can be placed in the truck)
Our trailer (2011 Airstream 25 FB, just under 26 feet long):
GVWR: 7,300 lbs. (the max weight of the trailer plus trailer cargo plus full holding tanks)
Base Weight: 5,600 lbs. (the weight of the trailer with no cargo and empty holding tanks)
Tongue Weight: 837 lbs. (the amount of weight of the trailer in the front at the tongue, counts against the payload of the truck)
Based on the above weight ratings, you can see that:
- The towing capacity of our truck is 11,200 lbs., and the GVWR of our trailer is 7,300 lbs. That gives us an excess capacity of 3,900 lbs (over 53%), which means we could upgrade to a larger trailer and still have a buffer. If we were really negative, and assumed our towing capacity was 9,500 lbs. (GVWR - GCWR), we would still have a buffer of 30%.
- Our payload (1,866 lbs.) minus our tongue weight (837 lbs.) minus our hitch weight (195 lbs.) gives us 834 lbs. Subtract out humans and felines and we are left with 430 lbs. If we have two full 6-gallon water jugs that's down to 330 lbs. A "small" 2000W generator and that's down to 270 lbs. of payload. The numbers can add up quickly. If you are close on payload you can opt to carry some cargo in the rear of the trailer, as long as you don't go over your trailers GVWR or your towing capacity. For us, we have excess towing capacity so if payload becomes an issue, we can carry more things in the rear of the trailer.
- The base weight of our trailer (5,600 lbs.) plus full holding tanks (996 lbs.) is 6,596 lbs., which means we can carry an additional 704 lbs. before reaching the trailer GVWR of 7,300 lbs.
Now that you have an idea of what all the numbers and weight ratings mean, you can pick the appropriate tow vehicle for your trailer, or the appropriate trailer for your tow vehicle, if you already own a tow vehicle.
For more about our towing vehicle selection process, please see Part II.