Roger, our region’s President, has been doing some local autocrosses lately, and I guess he got to thinking about what MIGHT happen if he tried jumping a curb at full-tilt like he did one time (ask him about it sometime) and got it upside down! So he decided to install a four-point roll bar and a racing safety harness. We took some pictures during the roll bar install to help you visualize what’s involved.

The bar that Roger installed in his car is what’s known as a Hard Dog Hard Core Double Diagonal Hard Top. Wow, that’s a mouthful! More often, it’s just called a HDHCDDHT for short. What all that means is that this particular roll bar is made by Hard Dog (HD, actually Bethania Garage, Bethania, NC). It’s the Hard Core model (HC), and it’s made of 1 ¾" diameter tubing which generally meets the requirements for SCCA Solo I racing (timed events with a single car on the course at a time). The Double Diagonal (DD) part means that it has two, shorter diagonal braces, rather than the standard single diagonal, which supposedly provides better rearward visibility.

Most types of roll bars will reduce the visibility through your rearview mirror, but the diagonal braced types limit it even more. The Hard Top (HT) designation means this bar is about 1" shorter than the standard Hard Core model, so that it will fit under the Miata’s OEM hardtop – the standard Hard Core will not. There are many other makes and models of roll bars, to fit many other needs, from style to pure racing. You should do your research before buying a roll bar, keeping in mind what your particular requirements might be. Be aware that for most on-track driver’s schools or driving events, the organizers will require a "four-point" type roll bar for all convertibles, with "substantial rearward bracing". The Hard Dog Sport and Hard Core Models both meet this requirement. Style bars (such as those by Racing Beat) and other two-point mount bars do not. In most cases, an OEM hardtop is not an acceptable substitute for a 4 point roll bar.

All that said, it’s my opinion (and that of many others) that a roll bar is an essential safety feature for any convertible, whether you’re planning on doing competitive events or just driving on the Parkway. It’s not that you intend to get in an accident or roll your car over, but, as the saying goes, those things happen, even on the street.

So, let’s see just how difficult it is to install a four-point roll bar in a Miata:

Here’s a picture of the HDHCDDHT bar before it was installed in Roger’s car. This is looking from the rear, showing the double diagonal bracing and the horizontal "harness bar" for attaching your racing shoulder harness. The double diagonal bracing gives you a small "v" shaped window through which you can hopefully see traffic with your rearview mirror. The standard diagonal goes right through your field of vision, but you can get used to it.
A front view of the roll bar. The standard finish for the Hard Dog bars is black powder coat enamel. Other colors may be available, and it can also be purchased in polished stainless steel.
Here Roger has laid out much of the hardware and pieces that come with the roll bar. Check the parts list in the instructions closely to verify that you’ve gotten all your hardware. You may need to make a run to the auto parts store to pickup some additional Grade 8 hardware if any is missing. Laying out the hardware on a rag, as Roger has done, is a good way to keep track of all your parts. In a few cases, you will need to reuse the original fasteners that come off the car, so don’t throw anything away just yet.
Roger, removing the seat belt retractor assembly and upper guide from the frame. There are three separate bolts attaching each retractor/guide assembly. Note that at this point, Roger had already removed much of the interior carpeting, trim, padding and insulation covering the package tray area behind the seats. To ease the job and give yourself adequate working room, you should remove both driver’s and passenger seats as well. The seat belt retractor will be reinstalled once the roll bar is in place, and the upper guide will be bolted to a tab on the bar.
An interior shot showing the package tray area with the aluminum cover removed. The rectangular shape is the interior sheetmetal covering the fuel tank below – bet you didn’t know it was that close! The small silver cover over the gas tank gives access to the fuel pump and tank level sender, should you ever need to get to either of them. We won’t need to remove it for our roll bar install.
Black marker shows the necessary material to be removed, to provide the required clearance for the rearward bracing of the roll bar. The two brace bars penetrate the package tray here, and run down to mount to the vehicle frame below in the trunk. Don’t worry about making this cut real smooth, as it will be hidden from view once you trim and replace the padding, insulation and carpet around the bars.
Our President, Roger, shown next to his new HDHCDDHT bar. The bar is being test-fit in the car to determine where the clearance cuts need to be made. The bar may need to be put in and taken out several times, to test the fit and make adjustments, so make sure you have a helper. The bar isn’t that heavy, but you need help to avoid snagging wiring, damaging upholstery or scratching paint.
Interior shot, showing the rear package tray with the clearance slots cut in the sheet metal. The cuts are approximately 2 ½" wide by 4 ½" long. Cutting the sheet metal is best done with an electric metal nibbler, but can be done with sheet metal shears or a reciprocating or jig saw with metal blades. A Dremel tool with a cut-off wheel can come in real handy for trimming and difficult cutting situations. Be careful not to scratch or damage the convertible top or plastic window, which will be very close to the work area. Maybe you should cover them? Smooth the edges of the cut, as necessary, remembering that appearance is not critical here since they will be covered up later.
Photo shows trial fitting of the roll bar after sheet metal slots were cut, to verify all clearances and bolt alignments. Careful, as it is all too easy to snag a wiring harness, cut the upholstery or scratch your pristine paint during this step! Be aware that most installers of Hard Dog roll bars report that one or more bolt holes did not align adequately to allow assembly – production tolerances, I guess! Don’t worry, just get out your trusty Dremel tool with a grinder bit, and enlarge/lengthen the holes to fit. This can be done with the bar in the car, saving you the time and aggravation of removing and refitting it one more time. Barely visible in the photo is Roger’s very nice DeWalt rechargable drill, with a long 12-18"x3/8" drill bit used to drill the first mounting hole in the rearward brace bar mounting plates from the top. Be careful to drill this hole so it misses the frame rail under the car. Look under there, you’ll see what I mean. Once this hole is drilled, you can fit up a bolt and nut to secure and locate the corresponding lower reinforcing plate under the car. This allows you to drill the remainder of the mounting holes from the bottom, through the pre-drilled holes in the reinforcing plate.
This shot shows the lower front mounting plate, with the three mounting bolts and washers in place, securing the bar to the bulkhead behind the seats. (See Picture #14 for corresponding reinforcing plates under the car) This area will later be covered by the carpeting and the seats. 1994 and later Miata owners, you will also need to remove and trim the mounting tab for your computer unit, which is located behind the passenger seat, to clear the bar’s mounting plate. Note the re-routing of an existing wiring harness around and behind the roll bar. Once the bar is in place and secured, you will not be able to change this, so get it right now! Be careful not to pinch or cut any wiring. NOTE: Apply some silicone sealant or caulk under each mounting plate when installing the bar for the final time, so that no moisture can find its way up through the bolt holes.
Detail shot from above, showing the mounting plate for the rear brace bar, running down through the clearance slot cut in the package tray. Mounting plates are bolted into the structure just ahead of the upper shock mounts within the trunk. There are three mounting bolts, washers and nuts. (See Picture #13)
Interior shot with roll bar installed and bolted in place, prior to re-installing the aluminum package tray cover. Double-check the fit, routing of wiring, seat belt routing and anything else before evenly snugging up all the mounting bolts. Double-check the tightness of all bolts and nuts.
Trunk shot, showing the lower mounting plates of the back brace bars, mounting to the body just ahead of the shock mounts. These will be hidden from view once the spare tire and metal plate over the fuel fill pipe (if you have one) are replaced. Don’t forget to trim and replace the fiber sound insulation panels around the lower bar mounts.
Shot under the car, near the wheel wells, showing the reinforcing plates and mounting bolts/nuts for the lower front mounting plates located on the bulkhead behind the seats. Coat these with a spray undercoating you can get at the auto parts store. Replace the plastic mud shields that you removed earlier from this area.
Roll bar installed, aluminum package tray cover reinstalled. Still to be done is reinstallation of plastic trim, insulation and carpeting. Some of the plastic trim must be trimmed to clear the new roll bar, which is now occupying the same space previously occupied by the trim. This is a good job for your Dremel tool with a plastic trimming bit, and requires a bit of patience for the necessary cut-and-fit routine. Take your time and get it right! You can finish off the raw plastic edges with some black vinyl door edge trim from Advance or Autozone. You’ll also have to cut your carpet and underlying padding/insulation to fit around the rear brace bars.
Roll bar installed and LOOKING GOOD! Makes a Miata look more serious some how, doesn’t it? Roger will wrap things up, take her (him?) off the jack stands, and take him (her?) for a spin. I predict he will be very pleasantly surprised at the very noticeable added stiffness of his Miata, especially since it’s an earlier one without many of the OEM chassis braces.

SOME PARTING NOTES ABOUT THIS AND OTHER MIATA ROLL BAR INSTALLS:

• Despite what it may sound like, this is not a really hard installation to do, as long as you have the proper tools and an assistant. I think what we found was that having someone who has done at least one installation before makes the process go MUCH faster, as there is less mystery to the instructions and the process ("Why do they do it that way?"). Our install took about 3 ½ to 4 hours, not including the preparation time Roger took to put his car on jack stands, remove the trim and carpeting, and remove the rear wheels. It also does not include the time required to carefully cut the carpet and plastic trim to fit. That time will vary in direct proportion to how careful you are and how good you want it to look afterward! Tools you really should have on hand: Open end and socket wrenches to fit all hardware (OEM and roll bar), a long 12-18"x3/8" drill bit and power drill, a Dremel tool with metal and plastic cut-off bits, and a power metal cutting tool such as a sheet metal nibbler. Other sheet metal tools will do in a pinch, as the sheet metal is fairly light guage (why do you think the Miata is so light?)

• As mentioned earlier, this install was for an M1 Miata. The install should be very similar for 99+ Miatae, but the Hard Dog roll bars for M2’s have slightly different rearward brace bars since they have to clear the non-folding glass rear window. Consult the instructions for differences. NOTE: For those who may have installed aftermarket convertible tops with glass windows on M1 Miatae, there may be a problem with installing a four-point roll bar! Check with the manufacturer.

• Note that in order to use your OEM convertible top boot (or a tonneau cover), you’ll have to modify the boot (or tonneau) to fit around the rear brace bars of a four-point roll bar. This can be done by any upholstery shop, or you can probably do the boot yourself, by simply splitting the sewn seam along the bottom. Fit the boot in place and you’ll be able to see where the seam needs to be split. Once properly modified, your boot or tonneau will fit around the bar, and the cover can be closed around the bar using velcro closures that will allow it to be removed again.

• You should really, really think about installing some type of padding on your roll bar, so you don’t knock yourself senseless in an accident (or near miss). Hard Dog sells a leather roll bar cover with padding that fits their Sport but not their Hard Core bar. Racing parts places like Racer Wholesale sell closed-cell roll bar padding foam in several colors, which can be used alone or you can have it covered with leather or vinyl by your friendly neighborhood upholstery shop. You can attach the foam padding with long zip-ties.

• With the four-point bars in M1 Miatae, you will no longer be able to unzip and lay the plastic window flat when you fold your convertible top, since the rearward brace bars will be in the way. What you can do instead is carefully fold the window as you drop your top, using a rolled towel or foam pool noodle inside the folded window to maintain a 2-4" diameter bend in the plastic, preventing kinking or breaking the plastic. Don’t drop your top when the temperature is below about 45 degrees F, since the cold plastic is more likely to crack when bent. You don’t really drive with top down when it’s below 45F, do you?

• SCCA Legalities: Hard Dog Hard Core bars are listed as legal for SCCA Solo I competition. This is somewhat dependent upon your height, as the top of the bar must clear your helmeted head by at least 2 inches. There also appear to be some questions about the configuration of the diagonals on the Hard Dog bar, since they do not connect into the main loop, as required by SCCA. But, a roll bar is NOT required for most classes of Solo II (autocrossing). Real road racing requires a roll cage, which is something else entirely, so get a copy of the SCCA rule book if you’re thinking about that. As mentioned earlier, if you are considering doing any kind of event on a race track, whether it be a driver’s education school or just an open-track day in your Miata, you will likely need at least a four-point roll bar.

That’s all! Go out and install a roll bar in your Miata, and stop worrying about your head!