Functional Roll Bars for Convertibles?
 

In light of the recent accident that hurleysurf24 had with his vert (https://www.rx7club.com/se-rx-7-forum-35/rx7-t2-vert-totalled-708249/), I was wondering who makes a stout functional roll bar? Not just one for looks. I was planing on buying one from Kirk Racing, but am not convinced that the upper seatbelt anchor points that they utilize as a mount point are entirly sound. What are your opinions and what other options are out there?
Keep in mind, I want the top to be completly functional which pretty much negates the use of rear angled bars.

There's also the Autopower one available through I/O Port Racing. As you say the top negates the possibility of having any rearward bracing. The only other feasable thing is a petty bar which goes from the middle of the bar to the passenger side footwell. This won't be as good though. You can also add door bars, but that won't really help support the top of the bar.

It'll be better than nothing, but obviously not as good as a full cage or a proper bar with rear legs.

You may not be able to escape those rear bars and keep functionality. You need cross bracing to prevent the roll bar from folding forward or backward in the event your car is sliding at a good clip when it flips over. A workaround might be possible but I don't know the interior dimentions of a vert well enough to offer any ideas outside of linking two roll bars, one in the back and one behind the windshield, which wouldn't be very pleasant to look at when the top is down.

I wouldn't worry about the seatbelt mounting points, they should be really solid. at least more solid than the freaking windshield. i always wondered how it would fair in a rollover situation, and know i know. sucks that hurleysurf had to find out the way he did though :( but at least he is alive and not missing any limbs.
do you have a link to the kirk racing ones?

You will NOT be able to have a truly functional roll bar and maintain full functionality of the top. It simply cannot be done. The only things you can do are buy the kirk bar and add door bars and additional bracing like what RX-Heven did.


Kirk racing does not show them on their site. I have emailed them over the last couple days and have just purchased a roll bar from them. I plan to mimic the setup that RX-Heven has in his car, but I want to try to have a similar harness bar for the passenger side as there is on the driver side. I dunno if that will work out though.

Images thanks to RX-Heven:
https://www.rx7club.com/forum/attach...d=185536&stc=1

https://www.rx7club.com/forum/attach...d=185537&stc=1

https://www.rx7club.com/forum/attach...d=185538&stc=1

https://www.rx7club.com/forum/attach...d=185539&stc=1

https://www.rx7club.com/forum/attach...d=185540&stc=1

https://www.rx7club.com/forum/attach...d=185541&stc=1

Kirk offers 2 flavors of roll bar for the FC vert. One which is just the hoop, and one which has a horizontal bar in the middle. RX-Heven started out with the Hoop with no horizontal brace. I asked Mark at kirk racing if they had pictures of the hoop + horizontal bar but he said they didn't have any. The Hoop is $250, and the Hoop with the horizontal bar is $295.

Thanks for the input guys and for the pics Juiceh. I have seen the amazing work that Rx-Heaven did with his bar setup. I too would like to integrate a harness bar for the passanger side seat as well as the driver. Perhapse a continuous harness bar without the diagonal brace? That would act similar to a standard horizontal bar.
As for the addition of the door bars, (correct me if I'm wrong) they don't offer any protection from upper hoop colapse in a roll-over situation. They are only there for side impact protection and lower cage support, correct? ( think I just answered my own question)
A petty bar is another option, but this is a street car with full interior that often has my wife in the passanger seat. I would rather not loose the use of it.
What about reinforcing the upper (seat belt) anchor points of the Kirk roll bar? Or perhapse the "B" pillars themselves?

Mine was custom made by Mitch Piper at www.pipermotorsports.com. He does superb work. The rollbar was SCCA Solo I legal when he did it (1997), but not race legal. So far, I've been able to use it at D/E events sponsored by NASA and others. His original design limits passenger seat travel a bit, so you can't date any tall girls, but my wife says I can't do that any way. She's 5'3", and the allowable seat travel is OK for her. The president of the Mazda Sportscar Club of Washington, DC had the first rollbar, and his 5'7" wife couldn't handle the lack of leg room. Mitch modified that rollbar to allow more seat travel, though he complained about the loss of strength compared to the original design.

http://www.cris.com/~Asam/20B.html for pictures.

George, it's a bit hard to see the roll bar in most of those pics. Where do the rear legs attach to the floor? It also appears that you had to make a custom boot cover to allow for the targa top sitting on said legs. Is this correct? If you could post any detailed pics of this setup that Mitch crafted, I would greatly appreciated it.

Yes, more pics please.


Without the diagonal brace you lose the protection from hoop collapse. So having a single harness bar may prove difficult.


Yup, side impact and lower cage support. I can't see them helping the rest of the hoop much.

Same here. Must be able to keep passenger seat, and as much passenger seat mobility as possible.


Thats an idea, dunno what can be done there except welding the anchor points themselves though, and that may not be a good idea..

Custom is the way to go. Try a shop that can make a bar that meets Sanctioned racing regulations.

You could have a cross bar on the rear legs to free up some room and still have some rigidity, but it's best to have one on the main hoop.

and make sure you're buying a ROLL BAR and not a STYLE BAR

Im pretty sure you could get some rearward triangulation while maintaining full function of the roof by running possibly two thinner (1 or 1 1/2" dia) tubes in parallel (one on top of the other) down around the edges where the hard tonneau cover sits, and then tie them into the rear shock mounts where the extra shock tower bracing in the verts already attaches. Depending on where you choose your attachment points, a slight kink may be necessary, and you'll need to cut some of the panels that cover the motors and stuff, but there should be room.

wouldnt rotormind be NotM this time?

I have a vert chassis outside my shop, and a tube bender inside. If anybody wants a custom bar without risking having welding done in their car PM me.

The area for mounting the shoulder point of a stock belt is VERY strong. There is always a few extra layers of steel and the metal with the threads for the bolt is usually thick and covers about 6-8 sq. in. around the hole. I have cut up quite a few cars to see this.

One of my first race cars was a FIAT X1/9 that I ran in IT. My rear hoop supports were triangle shaped plates that followed the length of the tube axis and bolted to the shoulder harness bolts. It passed anual tech for years in SCCA(early 90's) I don't know about current rules.

post up the pics. NOt everyone is as lucky as hurleysurf.

By saying "hoop collapse", do you mean the sides being drawn into the middle of the car from the force of the harnesses pulling forward? If so, wouldn't the fact that the harness bar being tied in near the seat belt anchors prevent this from happening?

This wouldn't be possible unless you had the ability to install rear legs. But I do agree with you.

toplessFC3Sman- I'm not quite following you. Can you please elaborate on what you were describing?

This is reasuring. As for triangle gussets to support the hoop above the seatbelt anchors; I don't think it would work in this instance due to how close the bar is to the anchors (i.e.- too acute of a triangle), but I may be wrong.

phoenix7-- The actual customization of the bar isn't the issue. Personally, I know a few people who have more then enough skill to build a proper bar/cage. It is the issue of designing a bar that is unobtrusive and still functional. As I mentioned, my particular car isn't, nor will it be, for track use; So meeting sanctioned racing regulations isn't a top priority. But those regulations are a good set of standards to shoot for if at all possible, I agree.

true, but as you mentioned : if it meets their criteria then it's more than enough for rollover protection. That's just my line of reasoning.

What I did forget was that some RACE vert cages are too large, at least to the point that the top is no longer usable.

tough cookies with the vert.

If you are doing a weld in bar you could go to the support beam across the width of the car instead of the floor.(you can always cut it out flush with the mounting plates later) Then you might be able to move the hoop behind the belt mounts. From the pics above it looks like the top function may be an issue, I don't know. I never saw the vert race car we have when it was a complete car with a roof.

i highly recommend john, the roll bar that he made for my coupe was totally awesome, beefy as hell
hopefully i'd never have to test its strength tho

fuck i cant find any pics

The problem with no diagonal bracing is that it can collapse sideways in an accident, sort of like how the rear legs help stop it from bending over when sliding along the ground. I know that cross bracing on the rear legs won't work with the top, but it's just to show that there can be other options. Miata bars do it that way.

A bar bolted to the seatbelt towers will be better than nothing, but having rear legs and a cross bar is much better.

Damn! After seeing Hurlesurfs' accident, I'm afraid to to drive my car without a fully functionable roll bar. I'm going to look into the Kirk roll bar like mentioned. My car is more like a... weekend warrior type thing (when its running). The passenger seat doesn't need to be all that functional. I figure if someone wants to ride in it. They'll make the sacrifice of not having much room! :)

Be sure to post up what you do decide to go with lov-2-rev.

^Ditto. I'd wondered about one a few times but now I think I might quit wondering and get thinking. If someone comes up with a working answer there's probably more than enough of us now who would be interested!

Yep, if they want it enough, they will accordian themselves in. You should have seen me in my uncle's Caterham 7. I'm 6'2 and there wasn't enough room in the footwell for my legs, so I had to put me knees up on the dash. Fun stuff!

Ahh. Got it. I had the whole "mouse trap" thing picture in my mind, but didn't consider it collapsing sideways, as in a rollover. Is it possible to connect the diagonal brace through a full width harness bar(i.e.-out of plain with the hoop) and still have it structural? If that doesn't make sense, think of it this way. A diagonal brace that angles backwards slightly, intersects with a full width harness bar, and has its own seperate mounting point just behind the passanger seat. I know it would be stronger if it tied back into the hoop at the bottom, but it would allow for a 2 seat harness bar, would offer some lateral stiffness and still allow full top and seat opperation. Or even make it a X-frame instead of a single diagonal.

I was planing on a bolt-in setup.
Hmm... If The hoop was moved farther back, wouldn't that give you less protection for your noggen? As for Rx-Heavens pics above........I know the top is still full opperational including the articulation of the targa top. It only clears the harness bar by about 1/8", but it works.

I'm starting to get the "thinkies". My brain is working overtime on this one and is starting to shut down. I'll come back to this with a fresh mind tomorrow.