DIY BRZ tire and fuel trailer build

[mkodama]

Warning
If you're trying to save money, this is not one of those DIYs!

Goal of this thread

• Document a build with information I can use in the future, or maybe somebody else too!

Goal of this trailer

• Get stuff from my house to the track where I compete in the Street Class of the NorCal 86 Drive Challenge link
• Carry a set of wheels with mounted 245/40-17 GT Radial SX2 spec tires link (fitting wheels and tires inside a BRZ suck)
• Carry 2 track days worth of E85 (not comfortable having this in the cabin with me)
• I'm space limited where I live so a tow vehicle and car trailer aren't a realistic option (FU too overpriced SF Bay Area property!)

How

• Trailer will be attached using a Slambert Twin Hitch link
• The trailer axles will be BRZ hubs so the trailer uses matching performance package wheels to get to the track in style, plus more spares
• The trailer suspension will be my original front struts and springs that have since been replaced with Annex ClubSpec Pros link
• In hind sight, it would have been cheaper to buy a Leroy Engineering Grid Tire Trailer link

I've got plenty of catching up to do and pictures of progress to get off my phone, but I think everyone likes vaporware CAD pictures, right?

[soundman98]

i understand using the same hubs for consistency a little, but why the struts? that commits you to a a-arm type setup that's not well known for towability due to the variety of alignment issues that can lead to trailer instability

i would suggest getting a solid trailer axle and leaf springs-- will keep the trailer tires better aligned for smoother towing.

there's also the harbor freight method
https://www.seriesblueadventures.com...-tire-trailer/

[mkodama]

Originally Posted by soundman98

i understand using the same hubs for consistency a little, but why the struts? that commits you to a a-arm type setup that's not well known for towability due to the variety of alignment issues that can lead to trailer instability

i would suggest getting a solid trailer axle and leaf springs-- will keep the trailer tires better aligned for smoother towing.

there's also the harbor freight method
https://www.seriesblueadventures.com...-tire-trailer/

Well, if I was smart and better with my finances I would have done that, but I’ve already made the whole McPherson strut setup work.

I also came across that site while doing my research, is that you?

[mkodama]

After a little bit of research and thinking, I just started ordering parts. I was traveling a lot for work at this time so all I could really do was order stuff.

• Practically new performance package wheels and tires from facebook marketplace. Not cheap but these were practically new, and performance package wheels are significantly harder to find. Also made a new friend buying these wheels! $700
  
• The cheapest strut bar I could find on eBay that supported the entire strut mount and had no hinges. This would keep the top of the struts in the right place and handle some of the loads without the chassis. $70.28
  
• Two spindles from a low mileage 86 on eBay. There were cheaper out there but the low mileage part and that they were from the same car and seller seemed nice. $174.78
  
• An 86 steering rack and front subframe from eBay. The fact that a used steering rack is under $100 was amazing to me. The steering rack also mounted to the front subframe to which I already needed to hold the control arms in place. $200.58
  
• I couldn’t find control arms on eBay that didn’t look bent, so I bought the cheapest I could find online from a website called Parts Geek. I don’t think I would trust these on my car, but for a trailer, sure. (They are already rusting they are so crappy) $103.69
  
• And like $100 of fasteners from https://www.subarupartwholesale.com/

[soundman98]

Originally Posted by mkodama

I also came across that site while doing my research, is that you?

no, that's not me. i don't believe he's extremely active here anymore. usually goes by stang70mustang or something similar. i ended up talking to him more on jalopnik than here, but he had the same screen name in both spots.

[mkodama]

All the parts arrived and I started putting things together on my garage floor. Assembling the front suspension outside of the car is amazingly fast and easy. Now a have a floppy semblance of an axle.

[soundman98]

the steering rack might add too much flexibility to the 'axle' might want to consider tying the tie rods straight to the frame later on to eliminate some of that play

[mkodama]

Originally Posted by soundman98

the steering rack might add too much flexibility to the 'axle' might want to consider tying the tie rods straight to the frame later on to eliminate some of that play

I’m not planning on leaving the steering rack with freedom to turn. I’ll get to posting that soon!

[mkodama]

Trying to figure out the layout at this stage of the build. I can see why struts and strut bars are generally a poor idea idea for trailers. I want to use the nice flat subframe to chassis mounting surfaces, but annoyingly this raises the floor maybe 6 inches up from when ground is, making the strut bar too low for tires or fuel jugs to fit underneath it.

At this stage, I’m mainly wondering how to tie the top of the struts to the subframe along with placement of the trailer frame.

[simpleisbest]

I wonder if the trailer will be too weight biased toward the rear and have too little tongue weight with the initial design, which would be bad.

In front you have 245/40-17 tire/wheel combo x4 probably weighs in about 46-48lbs ea.
In back you with full 5gal gas jugs are probably about 32lbs or so each x4, plus your bin with tools, spare parts, etc...rear weight can add up quick so you might need to take that into account.

I've built a couple harbor freight tire trailers over the years, so kinda been there done that

On the last trailer I built to hold a set of tires, large bin, plus 3 5gal jugs, I put the jugs in the middle. Seemed to balance well.

nice and creative design for sure

[ls1ac]

The HF trailer was 299.
As mentioned strait axel is the most stable way to trailer. Indipendeant tends to sway.
I have assembled several of the HF trailers as a basis for utility and motorcycle hauling. They have worked well.
Somehow I feel this is more of a personnel "I can do it " project.
If you look up trailer independent suspensions you will find that none of them use A arms and all use non-articulating axels.

[mkodama]

Originally Posted by simpleisbest

I wonder if the trailer will be too weight biased toward the rear and have too little tongue weight with the initial design, which would be bad.

In front you have 245/40-17 tire/wheel combo x4 probably weighs in about 46-48lbs ea.
In back you with full 5gal gas jugs are probably about 32lbs or so each x4, plus your bin with tools, spare parts, etc...rear weight can add up quick so you might need to take that into account.

I've built a couple harbor freight tire trailers over the years, so kinda been there done that

On the last trailer I built to hold a set of tires, large bin, plus 3 5gal jugs, I put the jugs in the middle. Seemed to balance well.

nice and creative design for sure

Trailer balance has definitely been a big thing on my mind. I’m leaning towards tires on the car side of the trailer axle, so that there is always weight on the trailer hitch for safety. Tools may vary, fuel jugs get used up, but wheels and tires are a constant.

My track wheels and tires are 44lbs each
the track wheels are about 2 feet from the trailer axle and 4 feet from the hitch
59lbs on the hitch with just wheels on the trailer
0lbs on the hitch with 20 gallons of gas and 50lbs of tool on the opposite side of the axle of the wheels.

Thanks!

Originally Posted by ls1ac

The HF trailer was 299.
As mentioned strait axel is the most stable way to trailer. Indipendeant tends to sway.
I have assembled several of the HF trailers as a basis for utility and motorcycle hauling. They have worked well.
Somehow I feel this is more of a personnel "I can do it " project.
If you look up trailer independent suspensions you will find that none of them use A arms and all use non-articulating axels.

I thought I couldn’t make that part any more obvious.

[soundman98]

Originally Posted by mkodama

I thought I couldn’t make that part any more obvious.

yeah, there's doing it yourself while ignoring all of reality, which normally ends up breaking something in a spectacular way, and doing it yourself while learning the how's and why's of established designs.

i'm glad i'll never be near you on the highway while you learn the first way.


i just worked at a house today where the homeowner had a very distinct "i can do everything" mentality. i counted 25 code violations walking between the driveway and the foyer. if he were to ever sell the house, it's likely that no mortgage company would ever take it on for the massive insurance liabilities it's got.

[mkodama]

Next on the list was to make something to replace the strut tower. I needed something to control just ride height, and caster angle, since camber is controlled by the strut bar and steering by the steering rack. I looked into buying sheet metal, but it seemed a bit restrictive and not rigid enough unless ALL the sheet metal was present.

So I decided to make this my first project designing something with spherical bearing rod ends. They would take care of some of the weird angles so that I don't have to measure them. They would connect to some threaded rod, and the other end would have a mount that attached to the T-slotted aluminum framing I planned on prototyping with. Added bonus would be tons of adjustability to change ride height and caster.

Added bonus picture at the end; you get to see my silly dryer-top TIG welding setup because I don't have much space. Aside from the lack of kneed room and uncomfortable chair, it worked pretty well!

1. Plan out manufacturing techniques; laser cut stainless and welding is super affordable, easy for me to assemble since I have a welding machine, and stainless so no need to worry about corrosion while it's sitting outside.
2. Figure out important dimensions and measure them. Get dimensions of pre-manufactured parts, which in this case were the rod ends, bolts, and nuts from McMaster-Carr. I hate mixing metric and inch, BUT using inch products gives me more options and better pricing. I decided to go a bit overkill and use 1/2" grade 8 cadmium plated hardware, because it barely cost anything extra.
3. Model it up!
4. Send part files out for laser cutting. I've been loving https://www.oshcut.com/ for instant quotes and the quality of their work.
5. Check dimensions of incoming parts. I didn't have a picture of me test fitting just the laser cut plate on the top of the strut.
6. Weld!
7. Check to see if the part actually works and you didn't just waste a bunch of time and money. (Pictures of fitment in a follow up post)