top of page

I Built a Tire Trailer!

Updated: Apr 5



At the end of this post is a summary of all of the major parts used for this project, including estimated prices and links, where possible.


This is a project I’ve been occasionally working on for the past few months, but I wanted to wait until it was complete to write up a formal blog post about it. My plan for autocross (and eventually track days and such) was always to have a dedicated set of tires for that purpose. What I also wanted was an easy way to transport them to and from these events, along with all of my other tools, without having to cram everything into the car. Yes, technically, all that stuff and more will fit into the the car, but it’s a real pain to have to load and unload everything every time. I wanted something that would allow me to literally “grab and go” and still allow me to keep the car clean, and empty for passengers or other cargo.


So that meant a trailer. And that meant a trailer hitch. On a BRZ. Meh.


What kind of Hitch?

There were two options I had when selecting a trailer hitch for the BRZ. The first was a “standard setup,” which involved bolting a big, heavy hitch to the chassis from underneath, and would result in a permanent installation that added weight and “ugliness,” in return for something that I was, realistically, only going to use every few weeks. The second option was a temporary hitch that installs into the rear tow points on the car, and can be easily installed and removed in basically 90 seconds. You can guess which solution I went with.


The Slambert Performance Engineering Twin-Hitch is a fantastic solution for people who want to tow something behind this car, or mount a bike rack or whatnot. It’s a bit on the pricy side ($300) considering that you’re basically buying two bolts, two bolt pins, and a bit of metal tubing, but it is well built, and everything fits together beautifully. Installation is something that literally takes less than two minutes: Remove the rear bumper caps, screw in the two pins, then screw in the hitch and you’re done. It’s stupid simple, as you can see in the video below. This hitch is rated to tow up to 1,000 lb, with up to a 100 lb tongue weight; both numbers realistically being more than you’d probably want to tow with this vehicle.



I also made two changes to the hitch once I had purchased the appropriate ball mount. I wanted to eliminate all of the clunking you get with the ball mount moving around inside of the hitch, because that noise gets transmitted straight through the unibody of the car, and is very audible from inside. First was to replace the ball mount pin with a standard nut and bolt. Unless you plan on swapping ball mounts, or changing between a trailer and a bike rack, you don’t need a quick-release pin. A standard nut and bolt can be tightened down to eliminate some of the clunking . The second modification was a hitch silencer (essentially a u-bolt and a metal backing plate) that snugs the ball mount up against the receiver, removing the rest of the movement. This completely eliminated all of the hitch noise that gets loudly transmitted into the cabin as loud clunks, and made towing the trailer a much more enjoyable, and less noisy experience.


A look at the Slambert Performance Twin-Hitch.
Here’s the hitch setup, complete with silencer.
This u-bolt and backing plate eliminates movement between the hitch and the ball mount, which in turn eliminates the clunking noise.

Building a Basic Trailer

So, on to the trailer itself. My goals here were simple: I wanted something reasonably small that could fit four tires, along with a box for my jack and the other items I tend to bring with me to an autocross. There are all sorts of options available, but in the end I went with a basic HaulMaster trailer from Harbor Freight (40.5″ x 48″). That seemed to be what just about everyone uses for tire trailers, and for the most part people don’t seem to have many problems with them. This is a trailer that comes in two boxes that can fit into the back of the BRZ, and which you must assemble yourself.


Assembling the standard Harbor Freight trailer.

For the most part, the assembly of the Harbor Freight trailer is very straightforward. The directions are pretty clear, and I feel like you would really have to try hard to screw something up. Basically you bolt the frame together, then you install the leaf springs and the axle, then you install the wheels (bearings first), and finally you install the lights. While most of the assembly process is fairly straightforward, there were a few annoyances that I’ll share here:


1. One of the wheels is slightly crooked. The axle and hub appear straight, so it’s the wheel itself that is bent. I might see if I can find a shop that can help me bend it back into alignment. In its current condition, the wheel wobbles back and forth about 1/4″ as it travels down the road. If you weren’t looking at the wheel itself, you wouldn’t notice, and I’ve towed this trailer many miles at over 70 MPH without any issues, but i do want to sort it out eventually.


2. The trailer won’t be square when you assemble it. Unless you have a proper jig to hold everything at exact right angles, you’ll assemble the frame and realize that the whole thing is slightly crooked. I actually only noticed when I went to fit a sheet of plywood as the floor, and my square piece of plywood refused to align properly with the trailer. This isn’t difficult to fix. In my case I loosened some of the bolts, and used a ratchet strap going from one corner of the trailer to the other to compress it until it was square, and then tightened the bolts again. This is only a temporary problem because once you properly fit a piece of plywood to the frame, it will serve to keep the trailer in the proper shape. In other words, the FLOOR of the trailer (which it is up to you to separately purchase/make/install) is what really provides the rigidity.


3. Harbor Freight’s engineers don’t understand how electricity works. The trailer kit comes with some side marker lights and some tail lights for you to install. I’m sure the lights themselves work fine, but I wouldn’t be able to tell you this because I blindly followed the wiring instructions in the Harbor Freight Manual, which make no sense. Essentially they have you ground the trailer near the tongue, and then they have you ground the lights themselves to the trailer frame. In theory, this would work because the trailer frame would act as a conductor and complete the circuit (much like how your car’s chassis acts as a ground.) However, this isn’t a “real” trailer that is welded together and then painted after the fact. This is an assemblage of individual parts that were all painted FIRST, and then screwed together, and that means there is no proper path for the electricity to take between the various pieces. Maybe it would work if you sanded down the paint before you put each bolt in, but that’s a lot of extra work that wasn’t mentioned anywhere in the Manual during assembly. In the end, I wound up rewiring the entire thing by actually running a ground wire directly to all of the lights, as well as the trailer, to ensure a proper ground. When I did this re-wiring, I also took the opportunity to swap the cheap bundled light assemblies with LED units (not the units you see in the above images.)


Conversion to Tire Trailer Duty

With the basic trailer itself fully assembled, it was time to turn this into a proper tire trailer! I decided that I would paint the trailer blue to match the car. Admittedly, I should have ordered a few cans of World Rally Blue paint off of Amazon ahead of time, but I didn’t, and then I spontaneously started this project one weekend and decided I would make do with whatever blue color Home Depot had, which turned out to be a lovely Sky Blue (HyperBlue?) No, I didn’t repaint the entire trailer. I figured there was no need to do extra work for no reason, so I just repainted the parts of the trailer frame that would be visible.The trailer also needed a floor. I got some nice, 3/4″ thick plywood from Home Depot to use as the flooring, cut it to size, drilled some holes for the bolts, painted it black, and bolted it to the trailer in 12 locations. A bit overkill, but since the floor is what gives the trailer most of its rigidity, I wanted it to be as solidly secured as possible. With the floor installed and completely bolted down, the trailer goes from being a wobbly collection of metal parts, to a very solid platform for loading heavy objects.


Semi-painted trailer frame. Also painted the fenders and the wheels matte black.
Half of the bolts installed. There were two more each for the front, center, and rear frame rails.

With the floor completed, it was time to mount the toolboxes. Most tire trailers I’ve seen seem to go with one massive box, but I decided to go with one big box, and one smaller box. This way I can carry all of my necessary fluids and other things in one box, without worrying about them spilling or stinking/greasing up everything else I take along with me. I like being able to put all the messy stuff in one box, and everything else in the other. I wound up getting a pretty big Husky toolbox, and a smaller Ridgid box. Both were originally rolling boxes, but I drilled out the axles and wheels on both (and removed the collapsing handles on the smaller box, which is why it looks, perhaps, a bit strange.) Installing them on the trailer was easy-peasy. Basically lined them up where I wanted them, and then drilled four holes straight through the bottoms and through the plywood underneath and bolted them into place.


With that done, it was time to figure out a solution to mount the tires at the rear. Eventually I do want to come up with a setup that allows me to slide a bar through the center of the wheels and lock them into place, but I want to plan that out properly, and perhaps get something welded to the frame rails to serve that purpose, so for the time being I just went with some ratchet straps. However, I still wanted something to properly cradle the wheels in order to make loading them easier, and also to ensure that they were always located at the same point on the trailer (to maintain the proper weight distribution.) I found that the simplest way to do this was with four sets of wheel chocks. I simply measured out where I wanted them to sit, and I bolted them right into the plywood floor. This is great because it keeps the wheels from rolling off the trailer when you remove the straps, and it makes for a slightly more presentable appearance than just a bunch of wheels strapped onto the trailer. I should point out that when the wheels are strapped down, they do not move a millimeter. They essentially become a solid part of the trailer, so there is no worry about them coming loose.


One cargo box, and the chock blocks installed.
Completed trailer with tires secured.
Note the addition of a second, smaller cargo box for fluids.

The trailer at this point was complete, but there was one other modification I wanted to make. In the configuration above, with the boxes full, the weight distribution results in a 60 lb tongue weight. This is well within the limits of the Slambert Engineering hitch, but my goal for the project was to keep the tongue weight under 50 lbs. This trailer is rated for 1050 lb of payload capacity, and I am carrying nowhere near that amount, so it is very tightly sprung. It isn’t so much an issue on the highway, but at slower speeds, it bounces around quite a bit because the leaf springs are very stiff. Therefore I decided to kill two birds with one stone, and add a bit of weight to the rear of the trailer, both to improve its low-speed road manners, and to bring the tongue weight down a bit. In the end, what I did was take two 25 lb exercise weight plates, drilled some holes into them, and bolted them underneath the plywood floor at the rear of the trailer. This 50 lbs added towards the back made a noticeable difference in how the trailer behaves on the road, and also brought the final tongue weight of the trailer down to 48 lb. That includes the tires, the small box full of fluids, and the large box full of tools and stuff, including a 100 lb floor jack!


(By the way, while you can use a standard scale to measure tongue weight, I highly recommend purchasing a digital hanging scale. It’s tiny and portable so you can keep it in the trailer to easily measure the tongue weight.)


Two 25 lb exercise weights as permanent ballast.

Driving Impressions: How does the BRZ handle a trailer?

First-off, let's clear some things up: Yes, the Owner's Manual says that you shouldn't tow anything with this car. No, that doesn't mean the vehicle can't tow anything. Certifying towing capacity for any vehicle is a lengthy, and expensive endeavor, and if towing capacity really isn't something that matters to buyers, the OEM isn't going to go out of their way to certify it. As a result, instead you have the kind of CYA language in the manual that, if you read between the lines, basically says, "Look, we didn't put this car through our towing certification program, so we're just going to tell you not to tow period."


In reality, every vehicle has SOME sort of towing capacity. Take my 2015 BRZ. It has a curb weight of 2,778 lb. and a GVWR of 3,682 lb. That gives you 900 lb to play with. Subtract driver weight (130 lb in my case) and I still have over 750 lb of leeway, which is more than this entire setup weighs. What that means, in practice, is that even with this trailer hooked up, the total weight of the vehicle still does not exceed the GVWR. Sure, there is added aerodynamic drag, but this is a relatively small trailer that doesn't contribute a ton of drag, and with only 50 lb of tongue weight, the trailer is doing most of the actual load-bearing.


With that said, how does it actually handle? Well I wasn’t sure what to expect because, at the end of the day, this car isn’t meant to tow anything, but truthfully, most of the time you’d be forgiven for forgetting you’re even towing a trailer entirely. It doesn’t pull the car oddly in turns, and it doesn’t move the car around at speed. In fact, the only time when the trailer is really noticeable is when you are accelerating or engine braking. And I don’t mean that you have to mash the throttle to go anywhere. The total weight of this trailer is no different than a rather large passenger, and some cargo in the trunk. It’s that same sense of, “Oh, right, I’ve got more than just ME today,” where you can tell the car is a bit slower than it otherwise would be.


Other than that, though, it really doesn’t make its presence known. It’s nice and quiet thanks to that hitch silencer, and I’ve done some rather spirited driving with the trailer with no ill effects. I've done 80 MPH around entrance ramps, and even swerved rather aggressively at 70 MPH on the highway, and the trailer is very stable, and if anything happy to drift around a bit behind the car. It also doesn’t obstruct your vision that much. You can see it in the bottom portion of your rear-view mirror, but you can see over it just fine too, so you aren't blind to what's going on behind you.


The only difficulty with this trailer, which is just a result of my inexperience, is reversing it. Put me in a 60′ articulated bus, and I will reverse it through a slalom and into a garage parking bay with ease (I used to actually do that), but this thing is so damned short that it’s an entirely different experience. I’ve gotten to the point now where I can reliably back it into my storage unit, but I still don’t feel comfortable backing it up anywhere where people are watching because I know I’ll wind up looking like an idiot. I’ll need to practice a bit more on that front…


LONG TERM UPDATES!

I wanted to come back to this blog and update it with some lessons learned after many years of utilizing this trailer. So here are a few key things I feel are important to point out:

  1. Re-pack the bearings! As it turns out, the bearings (at least at the time I purchased this trailer in 2016) were very poorly greased - to the point that really the grease it comes with should only be considered "shipping grease" meant to keep the parts from rusting during shipping. Buy quality grease, and re-pack the bearings!

  2. Make sure you use nylon lock nuts, or Loctite on all of the key bolts. After a year or two of bouncing around on the roads, bolts will come loose. I also recommend checking every single bolt at the start of every season just to be sure nothing is loose. In my case, the bolts securing the tongue to the frame had all come loose!

  3. If your trailer is going to be carrying far less than the loaded capacity, remove one of the leaf springs! In the case of my trailer, the leaf spring assemblies consisted of a small, medium, and large leaf spring. The large one is required since that's how everything works, but removing the middle leaf made a monumental difference in the trailer's compliance over bumps in the road. No more bouncing!

Parts, Links and Estimated Costs (prices as of 2016)

Below is a list of most of the parts needed to build the trailer that I’ve shown you in this post, along with the current costs of these parts. I’ve tried to provide links directly to as many of the parts as possible (the items in blue are hyperlinks, obviously.) I’m sure some of my non-Amazon links would be cheaper on Amazon, but I’m just linking to the actual items I bought at the places I bought them.


580 views0 comments

Recent Posts

See All

Kommentare


bottom of page