Hitches 101: The Mechanical Doo-Daws

I'm just starting to learn about trailer hitches and all that, and I need to organize and cement that knowledge by writing about it. So, at the risk of a blind-leading-blind scenario, here's a post on what I know so far!

In the following, I'll only talk about hitches and accessories for bumper pull trailers, the most common type of trailer for tiny houses, where the trailer couples with the tow vehicle in the vicinity of the vehicle's rear bumper. Some tiny houses are built on gooseneck trailers--for example, Clothesline Tiny Homes and MiniMotives--and I have not even wet a toe in the sea of gooseneck trailer hitch knowledge. All I know is that they couple with a receiver in the pickup truck's bed, over the rear axles, and this setup allows for a much heavier trailer. (Bonus info: gooseneck trailers are not the same as fifth-wheel trailers, but they are often confused with one another, I guess because they both extend over the pickup truck's bed.)

Essentials
There are three mechanical doo-daws that you need in order to connect your tow vehicle to your trailer. The trailer hitch, or receiver hitch, bolts onto the frame of your tow vehicle and is visible beneath the rear bumper (see post: Trailer Hitch is a Go!). The hitch is more or less permanent. When you want to tow something, you use a pin to attach the ball mount to the trailer hitch via the square-shaped receiver; the ball mount can be swapped out to suit the trailer. The ball mount has a hole in it where you screw in the hitch ball, which can also be swapped to suit the trailer.

The part of the trailer that cups over the ball and couples the trailer to the tow vehicle... um... also seems to be called the trailer hitch, for which I apologize.

(When I was first learning all this--like, last week--it just seemed like random, endless recombinations of the words "hitch," "ball," "mount," and "trailer," with some "receiver" thrown in for good measure. Trailer hitch... ball mount... hitch ball... hitch mount? Trailer ball? Ball hitch? Trailer mount? Ball... receiver?! Oh dear. I did finally comprehend the basic setup, and the terminology is slowly working itself out in my head, too, but it's not the easiest process ever.)

Weight Capacities, Sizes, and Other Variables
All of these components, plus your tow vehicle and your trailer, come with different weight ratings or capacities. The key point to remember: every component of your towing system must have a weight rating/capacity that meets or exceeds the weight of your trailer. If you want to tow a 10,000-lb tiny house on wheels, everything, from the truck to the hitch ball to the trailer, must be rated for 10,000 lbs or higher.

Hitch Ball:
For the job at hand at time of writing--getting the trailer home from Iron Eagle--we're looking at towing a relatively light trailer (since it's empty) that nonetheless belongs to a heavy, 10,000-lb weight class (since will have to support a house built on it). This means we need a heavy-duty 2-5/16" hitch ball to fit its trailer hitch, but everything else can be lighter-duty. Hitch balls come in three standard sizes, depending on the weight class of trailer they will fit: 1-7/8", 2", and 2-5/16", which haul trailers rated for up to 2,000 lbs, 8,000 lbs, and 30,000 lbs, respectively (source).

Hitch Ball Shank:
Our hitch ball has a 1"-diameter shank to fit the ball mount. The shank is the part of the hitch ball that screws into the ball mount; the width of the shank--3/4", 1" (most common), or 1-1/4"--has to match the size of the hole in the ball mount. Heavier trailers need balls with thicker shanks; our 2-5/16" ball with its 1" shank is only rated to 7,500 lbs, so when we're done with the house, I'm guessing we'll need to buy a ball with a 1-1/4" shank.

Ball Mount:
Heavier trailers also need appropriately heavy-duty ball mounts. It seems logical that the heaviest-duty ball mounts will have a hole to fit the heaviest-duty hitch ball shank, i.e., the 1-1/4" shank. Ball mounts also come with various amounts of rise/drop, which allows you to match the height of the hitch ball to the height of the trailer's hitch no matter the height of the tow vehicle. We chose our ball mount based mainly on the fact that it has an adjustable rise/drop, since we weren't sure how far off the ground our Toyota Sienna would put the hitch; it turns out the square receiver is about 10.5" from the ground, and the ball needs to be 18" from the ground, so we need a ball mount that can give us those extra ~8" of rise. Fortunately, the ball mount we bought can give us that much rise. Unfortunately, it is only rated for 5,000 lbs, so again, when the house is built, we'll need to upgrade.

Trailer Hitch:
And, of course, heavier trailers also need heavier-duty trailer hitches. Trailer hitches are classified into five classes, based on how heavy a trailer they can handle. Since the Sienna will only be hauling the empty trailer, we chose a medium-duty receiver hitch that matches the Sienna's towing capacity rather than the trailer's weight capacity. (Make sure the receiver hitch matches your vehicle! The one we ordered is the exact one for the Toyota Sienna, and it fit perfectly. It happens to be called a class III hitch, which would appear to be heavier-duty than the Sienna needs, but... oh well.) My completed house should weigh 10,000 lbs or--hopefully--less, so whatever vehicle eventually hauls it will need a class IV hitch.

Tow Vehicle:
Different vehicle makes and models have different towing capacities, and their towing capacities further depend on certain engine upgrades and whatnot that may or may not have been enacted in your particular vehicle. An investigation into our Sienna's VIN, at a local Toyota dealership, revealed that this particular vehicle has a factory-installed "tow prep package"; this means that its engine can handle a towing load of up to 3,500 lbs, instead of the normal 1,200 lbs. I'll need to use a much heavier-duty truck to tow my completed, 10,000-lb house. To get an idea of what's out there, here's a sort-of handy chart of different trucks' towing capacities.

Trailer:
Finally, the trailer itself will have a weight rating, based exclusively--as I understand it--on the rating of its axles. Iron Eagle's PAD Series trailers have axles rated at 5,000 lbs each, and the standard number of axles is two, bringing the weight rating of the trailer to 2 x 5,000 lbs = 10,000 lbs. Again, the axles can support 10,000 lbs--so that includes the weight of the trailer itself! A 20' trailer should weigh less than 1,600 lbs, according to Iron Eagle, meaning I should be able to put a house weighing at least 8,400 lbs on it. Because the load is expected to be so massive, it needs a heavy-duty hitch ball to connect it securely to the hitch--see above.

Kinds of Weight
Say I build a house that weighs only 8,000 lbs (thanks, SIPs!). It will have a gross trailer weight (GTW) of 9,600 lbs. That is, the weight of the trailer and the house and everything on it adds up to 9,600 lbs. Similarly, gross vehicle weight (GVW) is the weight of a vehicle plus any cargo, fuel, and people the vehicle is carrying. Trailers and vehicles have gross trailer weight ratings (GTWR--see above) and gross vehicle weight ratings (GVWR), which are the upper limits of what the GTW/GVW can be.

Tongue weight is the weight of the trailer that is transferred to the tow vehicle via the hitch. (The tongue of the trailer is the triangular piece in front.) It should be about 10%, and up to 15%, of the gross trailer weight. If you have too much weight on the tongue end of the trailer, leading to excessive tongue weight, it can bend your vehicle-trailer combination into a shallow "V" shape; to a point, you can correct this using a weight distribution hitch. On the other hand, if you have too little weight on the tongue end of the trailer, the trailer hitch may not fully couple with the hitch ball, and/or there will be too little weight on the rear tires of the tow vehicle for them to grip the pavement strongly enough to tow effectively--neither of which is good.

I believe that if a trailer is attached to a vehicle, the tongue weight is included in the GVW. The tongue weight added to the GVW definitely must not exceed the GVWR, since the tongue weight is, in fact, adding to the stress on the vehicle's tires and axles.

Changin' Gears, an RV website, has an easy-to-understand breakdown of the different kinds of weights, and Hitching Up has a good glossary of terms, too.

If any of this is confusing, you know, don't worry about it. Unless you're about to buy towing gear for your own towing project, in which case, study up! And maybe check out some trailer/towing/RV-specific websites for the final word, rather than take mine. Let's be honest, here.

I'll cover the electronic aspects of trailer towing--the wiring harness and brake controller--in another post, once I have the beginnings of a grasp on how they work.