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  • Convertible roll bars question

    Hi there, I had a couple questions about roll bars for convertibles, hopefully this is the appropriate place to post.

    I'm interested in participating in OTA this year for the first time and I'm looking at getting my car ready to meet safety/technical. It's an NB miata, so I know I'm going to need some sort of roll bar. Initially I was very close to getting a "hard dog M2" bar, but now I'm unsure if it meets the requirements. I'm partial to the bar since it's the most common and I'd pretty easily be able to get one locally for a good price.

    In particular, from 1.3.4 iii): "A straight diagonal brace running from one main hoop upper corner (typically along the horizontal portion, just inboard of the upper corner radius) to the opposite side vertical tube as close as feasible to the floor mounting plate."

    Now most of the hard dog bars I see locally are the double diagonal like below, which I'm guessing outright don't meet the definition...



    However, looking at the single diagonal it still doesn't seem to fit the definition, as it's not quite at the top opposite corner:


    So my first question is, does this seem (at least design-wise) to fit the requirements? And if not, as a follow up question, what do the other guys racing miatas tend to use? I know I'm not the first guy to show up to OTA with one so hopefully somebody could chime in with that.

    Thanks!

  • #2
    Re: Convertible roll bars question

    Hi thatCamden!

    I can relate since I have a convertible and have been doing OTA for the last couple of years (hilarious story about me almost getting in three years ago) but I went through the same stuff with my S2000.

    According to the ruleset from 2018:

    DESIGN
    .3 The roll bar shall be designed to withstand compression forces resulting from the weight of the car coming down on the roll structure and to take fore and aft loads resulting from the car skidding along the ground on the roll bar
    structure.
    .4 The roll bar will have a minimum of four pieces of same diameter and tubing thickness:
    i) A main hoop formed from a single piece of tube, die bent with no crimps and a maximum of four radiused bends, spanning the full width of the cockpit. Radii shall be at least three times the tube diameter. It shall reach a minimum of two inches above the driver’s helmet or as close to the roof as possible while not deviating more than 10 degrees from vertical. It shall not be more than 254mm / 10” behind the driver’s helmet.
    ii) A straight diagonal brace running from one main hoop upper corner (typically along the horizontal portion, just inboard of the upper corner radius) to the opposite side vertical tube as close as feasible to the floor mounting plate. It is highly recommended that the tube ends be within 100mm / 4” of a backstay and a mounting plate.
    iii) Two (2) straight fore/aft braces attached as near as practical to the top of the main hoop, no more than 150mm / 6” below the horizontal portion of the main hoop. They must be mounted as close as possible to the side panels and form an angle of at least 30 with the vertical.

    I think you're confusing the ii section for the diagonal running left right (driver to passenger side) but I interpret the rule as the diagonal running front (main hoop) to the back (rear floor mounting point). Your NB Hard Dog Miata hoop has this.

    Section iii states that you essenitally need the double diagonal variant of the Hard Dog hoop.

    I specifically run the following Hard Dog Hoop in my S2000 as did a John P. from the CCDB so it's legit. 4th picture to the right on my Instagram.

    https://www.instagram.com/p/BSnAg9GF..._web_copy_link

    Hope that clarifies things!

    Kev
    Kevin Wong
    GT3 / STR / C-Stock Plus Honda S2000 #111
    2020 OTA Chief Timer

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    • #3
      Re: Convertible roll bars question

      Originally posted by LemonJus View Post
      I think you're confusing the ii section for the diagonal running left right (driver to passenger side) but I interpret the rule as the diagonal running front (main hoop) to the back (rear floor mounting point).
      I'm not sure how you're interpreting it that way. It literally says "from one main hoop upper corner to the opposite side VERTICAL tube as close as feasible to the FLOOR mounting plate." How many vertical tubes do you have at the back (rear floor mounting point) of your roll bar?
      Last edited by Snizzoop; 02-11-2019, 09:27 AM.
      TLMC Autoslalom Co-Director

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      • #4
        Re: Convertible roll bars question

        Originally posted by Snizzoop View Post
        I'm not sure how you're interpreting it that way. It literally says "from one main hoop upper corner to the opposite side VERTICAL tube as close as feasible to the FLOOR mounting plate." How many vertical tubes do you have at the back (rear floor mounting point) of your roll bar?
        I re-read that rule again, you are correct good sir.

        I have put forth the question to the OTAO to confirm intent and possibly correct the rules.
        Kevin Wong
        GT3 / STR / C-Stock Plus Honda S2000 #111
        2020 OTA Chief Timer

        Comment


        • #5
          Re: Convertible roll bars question

          Thanks for the follow up guys, I should have attached the provided sketch from the rules for clarity on what I meant, too:



          This is just below the rules in question, the red bar is the diagonal I'm concerned about. Interestingly this one says "minimum one diagonal" so maybe there was meant to be room in the rules for double diagonal or other setups?

          I'll just wait for now till you hear back, it's no rush for me since I'm not really keen on doing any work on the car till it warms up, haha.

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          • #6
            Re: Convertible roll bars question

            I Raced a Miata and I used a double diagonal Hard Dog and it passed the test.

            There are other types out there, but the Hard Dog was useful because it wont take up leg space by allowing you to drop the seat all the way back. This might not be an issue unless your tall like me 6'2.

            I also visited the plant in NC and it really is a well built unit based on what they showed me and it actually looks cool because it makes the miata look harder edged.. if that can be for a Miata.


            What year is yours? Mine was the one you could use with a glass rear.

            I know of a few available so let me know how your hunt progresses.
            BadGer Racing:OTA#97 VW Passat, NB Miata, Infinity G35 6mt Coupe, Volvo C70 HP
            BRC Ice Racing #97

            Comment


            • #7
              Re: Convertible roll bars question

              Mine's a 2001, I've also got the glass rear window in my soft top, though I'd like to eventually go to a hardtop. If it's legal I'm definitely going to go for the double diagonal, but as the others mentioned above, maybe the rules have changed this year on that?

              I'll give you a shout once a know for sure, it would be nice to pick one up used and save a few bucks.

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              • #8
                Re: Convertible roll bars question

                If the rule says "minimum one" then two, three or seven is ok.
                Barry

                Citizen Cone Dodger

                Comment


                • #9
                  Re: Convertible roll bars question

                  If the rule says "minimum one" then two, three or seven is ok.

                  Have run a double hard dog and a double CSC bar before and passed tech.
                  Barry

                  Citizen Cone Dodger

                  Comment


                  • #10
                    Re: Convertible roll bars question

                    Originally posted by Saj5DJ View Post
                    If the rule says "minimum one" then two, three or seven is ok.

                    Have run a double hard dog and a double CSC bar before and passed tech.
                    Exactly double-diagonals are fine. Make sure that the diagonals mount at proper locations per the rulebook. I recall the NB version being fine for that.
                    CASC-OR Time Attack Director

                    sigpic

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                    • #11
                      Re: Convertible roll bars question

                      The graphic you posted would do fine for sedans and coupes. Not much space in a Miata so everything is condensed but still applies.

                      Keep in mind the Hard Dog bar is Legal for SCCA Time Trials and NASA HPDE Events when equipped with at least one diagonal brace.

                      The owner of the company use to race Miata's and is pretty knowledgeable.

                      Have a look at the website and check out their survivor crash pics to bring the message home.

                      http://www.bethania-garage.com/why.htm

                      Saying that, I know our OTA treasurer, Rob H. also just purchased a different one for his street driver which is also an NB (he races a green NB in this series). He took another route on roll bars and you might get him to "pipe" in on his thoughts.

                      Barry who just commented (saj*) was also a great competitor in OTA and auto slalom and has great advice. (Barry did you sell all your Miata's yet?

                      Another competitor in the Champion RX-8, Alex,(and one of the Scrutineers) is affiliated with Dave's Garage who specializes in Miata's (specially if you want to install a corvette engine in it).

                      All these are great resources for your initial research.

                      I also know of a red hardtop for a Miata if interested.
                      Last edited by CarVolvo; 02-14-2019, 12:19 PM.
                      BadGer Racing:OTA#97 VW Passat, NB Miata, Infinity G35 6mt Coupe, Volvo C70 HP
                      BRC Ice Racing #97

                      Comment


                      • #12
                        Re: Convertible roll bars question

                        Originally posted by CarVolvo View Post
                        Another competitor in the Champion RX-8, Alex,(and one of the Scrutineers) is affiliated with Dave's Garage who specializes in Miata's (specially if you want to install a corvette engine in it).

                        All these are great resources for your initial research.

                        I also know of a red hardtop for a Miata if interested.
                        I went this route. Pretty said "SHUT UP AND TAKE MY MONEY AND LET ME IN."

                        Didn't so much as read the rule book as simply 'get me what it takes to get legal at OTA'.
                        Kevin Wong
                        GT3 / STR / C-Stock Plus Honda S2000 #111
                        2020 OTA Chief Timer

                        Comment


                        • #13
                          Re: Convertible roll bars question

                          Originally posted by CarVolvo View Post
                          Barry who just commented (saj*) was also a great competitor in OTA and auto slalom and has great advice. (Barry did you sell all your Miata's yet?
                          Yup! But I seem to co-own an NC now, which is kinda like a Miata :P

                          Will join you guys again some day, hopefully before I'm old and slow. Best of luck with everyone's planing for the 2019.
                          Barry

                          Citizen Cone Dodger

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                          • #14
                            Re: Convertible roll bars question

                            For those of you with NC's requiring roll over protection, you should have a conversation with Perry who was our past chief timer. He figured out retrofit for the car.
                            BadGer Racing:OTA#97 VW Passat, NB Miata, Infinity G35 6mt Coupe, Volvo C70 HP
                            BRC Ice Racing #97

                            Comment


                            • #15
                              Re: Convertible roll bars question

                              Thanks for the info guys, I feel like it's safe to say the Hard dog double diagonal is fine for tech. I'll either grab a used one or maybe give Dave's garage a call if I'm feeling particularly lazy.

                              Hopefully I'll see you on the track in a few months!

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