It came up on another thread but I felt it deserved its own thread.
This is what I made see pictures. Attaches to spec Miata tow eyes.

1) The whole hitch and all the mass associated with it can be installed or removed by 2 bolts in seconds using a crescent wrench.

2) I think it will work with my planned DIY underbody treatment and rear diffuser as well.

Bob

 

A note to others since I see you already have it- Run Grade 5 bolts on your setup. The hitch WILL flex, and grade 8 bolts shatter, while grade 5 will flex with it.

Your setup looks great!

 

Interested in making me one?

 

I used 3/4" bolts they are huge. I welded two washers together for the outer washers. A smaller one fits in the ID of the tow eye and keeps it centered and the larger one clamps down on it.

I got the hitch receiver and tubing from a welding shop that makes things like trailers and hitches.

Bob

 

Resurection per a recent tire trailer thread.

Bob - To be clear, in the attached picture, part "B" slides up in to part "A"? I assume you leave "A" bolted to the tow eye all the time and remove the rest by unbolting the large bolts that pass through the lower hole in the tow eye?

 

Correct. The little reciever parts that remains bolted to the car don't weigh very much though.

The hitch slides up into the two small recievers easily and dosnt slide down while your putting the bolts in.

Bob

 

The more I look at hitches, the more I realize that is pretty damn clever. Maybe Rennenmetal would be willing to build something comparable to be sold with the tow eyes.

 

Sombody should make it for sale that is for sure.

Bob

 

Yeah I need to find someone to build me one for sure.

Happen to have some measurements from when you built it bbundy?

 

I didn't measure anything I built it on the car. The concept is awesome though and a smart vendor should try and copy it. It is not like I'm going to apply for a patent or anything and I'm too lazy to get into producing the Idea myself for retail.

I also have a bike rack design worked out that uses the outboard attachment at the tow hooks. It holds two bikes with fork mounts so no bikes swinging around by the top tube beating against the body of the car nothing touching painted surfaces of the car and you can open the trunk without pulling the bikes off. It is light weight as well.

Bob

 

Sent you a PM.

 

I'm going to make one of these for myself! Thanks Bob.

I wonder about liability if it went into production though. How strong it really is mounted to tow hooks. You know some yahoo would load up way to much weight, use aluminum tow hooks and have things go bad. Said yahoo will just happen to be an attorney.

 

Whoever decided to take on producing these would have to test it to the max to insure safety. You'll stand out enough towing with the miata, last thing you need is to have the ****** snap off and smash the guy behind you.

I have a neighboring welding shop that would make them if I gave the guy the measurements.

 

Have you taken a close look at some of the hitches that are being produced for different vehicles? based on some of the stuff I have seen I don't think the risk of liability is that high with a reasonably well thought out design. The tow hooks Im using are every bit as strong as the brackets used to attach most other trailer hitches. the chassis is the weak link.

Bob

 

bbundy, what you have done there is beyond clever. Very well done. Yes someone should produce this. Flyin Miata decided there is enough of a market that they paid someone to do FEA on a lightweight hitch they now offer. Hard Dog has been selling them successfully. If yours removed 90% or more of the weight and is good for the lightweight track tire hauls we all need, I think it's a no brainer.

Well done.

 

Details on the trailer you will use?

 

My problem with producing this is you're shooting for a market somewhere between the DIY option of roughly $50, and FM's cost of $225. Not much room there.

 

This is appropriate for the little Harbor Freight trailers that are popular with the track day crowd. I've seen this in person and owned/installed the Hard Dog bit for the NB. Bob's design is just as strong but 95% of the mass unbolts when you get to the track. The Hard Dog I carried around for 2+ seasons put ~15 pounds of mass on the car permanently... until I bought a proper tow rig/trailer and took it off.

 

Several companies have gone through the trouble of developing a hitch. FM, Hard Dog, DLan etc.

It's just they have all followed the same design concept in doing so in permanently attaching a big chunk of mass to the car.

With this concept the design doesn't have to be light and wimpy to reduce weight because all the mass comes off in seconds, it’s not permanently attached to the car.

It works slick. I have been using it for a number of years now.

Bob

 

Care to share any details/links for this method? I haven't found a way to reasonably put a hitch together for less than $100 or so.