You want to build a cage that is as far toward the outer edges of the passenger compartment as possible. This increases chassis rigidity as well as driver safety. In order to do so, you need to strip the whole interior.
When we brought the car in, the first step was to strip the interior. As we removed the carpeting, we discovered the previous owner was kind enough to Dynamat the whole car. Woodford smiled, handed us a scraper, some acetone, a chunk of dry ice and said: "Have a party." It took almost two days of knuckle busting to get that crap off. Not removing the material from the car would have caused problems when welding onto the floorpan, as even Dynamat becomes combustible under the heat of a welding torch. We weren't looking to add 'burned to the ground' to a project history that includes vandalism and theft.
The cage starts life as a confusing pile of bent tubing, pieced together multiple times, then removed for welding, adjustment, or perhaps just for our personal aggravation. This process ensures the best possible fit.
In the event of a rollover, the pedestals supporting the cage need to distribute the weight into the chassis rather than punching a whole straight through it. The pedestal thickness and mounting, in addition to the cage itself, all have to be made to the sanctioning body's specifications.
As driver safety and chassis strength is paramount and non-negotiable, we elected to fit AWR's standard door bars, requiring the removal of the driver's window. The door bar protrudes a couple of inches into the door area to give added deflection space before the cage intrudes into the driver's pelvis in the event of a side impact.
If it's steel or chromoly, a cage adds weight in exchange for improvements in rigidity. We originally intended to build the cage to NASA class regulations for Spec Miata, but this falls outside, because of the additional attachment points that make it as stiff and safe as possible. With what we have planned, it won't meet the requirements for this wheel-to-wheel class anyway. The cage has eight points, as well as being attached on all three edges of the door sills with gussets reinforcing both A-pillars, and above and below the windshield. Per the NASA rule book, the seventh and eighth points attach to the firewall and have 360-degree welds at their mounting plates. These additions have turned our flexi flier into a car that can lift three wheels off the ground by putting a jack under one corner.
AWR has also made provisions for a window net and kill switch. This will be required for the class this car will end up in, but not for NASA's TT street classes.
Padding
Time required to mask off the cage: four and a half hours. Time to apply seven cans of Krylon: two hours. Time elapsed before we scratched it: four minutes.
Most of you have seen a moron driving a car with a cage, a stock seat, and no rollbar padding. For those of you who weren't sure, we assure you that mild steel has more tensile strength than your skull. You should avoid driving on the street in a cage-equipped car with no helmet. Also, when on the track, your helmet needs some help protecting you from the cage. NASA requires use of rollbar padding made of Ethafoam or Ensolite on any part that may come into contact with the driver. It recommend SFI 45.1 spec roll bar padding, so this is what we are using.
Seats And Mounting
With a maze of hard metal bars around you, it is extremely important to have a safe seat working with the race harness to keep your body from contorting itself around the curvature of the cage. We turned to Racetech, a sponsor of the SCCA MX-5 Cup Series, for our mount. Racetech offers seats that fit into every Miata. We used its RT4009 Head Restraint Seat. While it weighs about 20 pounds, it holds a six-foot, 175-pound driver comfortably. Prior to picking the seat, we tested it to make sure the harness holes on the seatback weren't lower than the driver's shoulder height. Often neglected, the position of the holes contributing to the harness angle can be extremely dangerous, as angled shoulder belts cause the spine to compress as the body moves forward in a longitudinal impact.