We had a fer options. There are racing fabricators who will install cages for $1400+. There is an Autopower weld in kit for about $650 (plus shipping, which can be substantial). Or, I could fabricate the whole thing out of DOM tubing I was planning on using for a different project. The cost of fabricating the cage is less, I was able to start it right away, and frankly I wanted the challenge. Thus we chose to have me fabricate the cage based upon a design in another spec Miata.

The design is to be fairly standard. A triangulated hoop with triangulated bracing to the rear, braces with 2 bends forward down the windshield pillar to the floor, cross braces across the dash & windshield top, NASCAR driver's door bar, x-brace passenger side, then tubes forward to an existing firewall reinforcement. We had to decide how to build the back brace, with some builders having it be straight, and some bending it, which allows for additional room to put the seat backward. This is best considering that a variety of people may drive the car, and it may need the additional legroom or layback. This "basic" design will take a total of 21 tubes and 14 bends.

To get ideas, I took some pictures of a spec Miata built and driven by a friend of ours. The cage is well built, and will serve as a template from which I'll build this Miata cage. Pictures are posted to the right.

The cage is to be attached at each of the 8 points through pads made out of 11 gauge steel. The purpose of these is to distribute the loads from the cage into the chassis more evenly. If you think about it, the tube attaches at about 1.75 square inches. A pad of heavy steel can be much larger. This helps prevent the tubing from "punching through" in an incident, as well as making the attachment more solid. At the most forward & rearward points, it will be a simple flat piece welded to the car. At the hoop, this will be a piece that is bent to follow the contour of the rear bulkhead. Where the a-pillar brace comes down near the door sill, I'll fabricate a wedge, weld it to the sill, and then attach the a-pillar brace to it.

The plan is to build the cage around the hoop. First step is to build the hoop as tight within the constraints of the hardtop that will be on for spec races. This must be precise, as any problems here will cause issues with the whole cage. From there, I'll build the bracing backward, tack things together, and then size and build things forward. I don't plan on welding anything together permanently until at least the hoop assembly is done. This will allow any last minute adjustments necessary.

In future articles, I'll show the car prep, building the hoop assembly, building the forward portion of the cage, and possibly even painting it.