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PRI Race Double hoop roll bar help needed

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jhollis Avatar
jhollis Jarrett Hollis
Visalia, California, USA   USA
I had looked for this roll bar for a couple of years and finally found one in 2015. To my knowledge they are no longer made.
I really like the roll bar but I cannot figure out how to get the seatbelt to work well with it. There is a flat plate welded onto each side which I assume offers some sort of re-mounting of the seatbelt. However, it is the wrong angle for the OEM unit.
Hopefully someone else who has one can give me some guidance.

The pic is copied from another thread on this forum.

Jarrett

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rhatchell Ron H
Columbia, South Carolina, USA   USA
1980 Triumph Spitfire 1500 "Charlotte"
My installation. Installed by PO.



Ron
"Charlotte" - 1980 Spitfire 1500


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jhollis Avatar
jhollis Jarrett Hollis
Visalia, California, USA   USA
Thank you Ron. The picture says it all.

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Azoth Shane G
Los Angeles, CA, USA   USA
Would either of you be able to post some more pictures of the roll bar? I really like the way it looks - perhaps it could be an inspiration for getting one made locally.

jhollis Avatar
jhollis Jarrett Hollis
Visalia, California, USA   USA
It will be a while. I’m in the middle of moving.

Herald948 Avatar
Herald948 Andrew Mace
East Nassau, upstate NY, USA   USA
Please educate me, as I know virtually nothing about structural engineering or design. Looking at this setup, I can't help but wonder how well this bar would retain its shape when...er...tested, particularly in the areas I circled. Am I nuts, or am I onto something?



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claytoncnc Avatar
claytoncnc Gold Member Marcus Clayton
Melbourne, Ivanhoe, Australia   AUS
You are not nuts Andrew, like most street rollbars, it would easily hold the weight of the car, and would probably hold several times that figure, but it would collapse at the points you indicate under the instantaneous load that happens in a high speed roll over.
At low speed, on the street, the loading is quite low, so the bar would be fine, in a high speed flip and multiple rollover, it would almost certainly deform, the point of collapse is somewhere between the two.

True rollover protection makes an open car impractical for the street.

I have a bar in my car, that I know will not stand a high speed test, but I feel it provides some measure of protection.

I have rolled 4 cars in the last 40 + years, 2 on rallies, where I have miscued, and the car has near stopped before gently toppling, one on a back road, again the car had almost stopped before the roll. On these occasions, even the flimsy bars being discussed would have no trouble in staying intact.
The other roll was a 100mph job, on the track, the car rolling 5 times including an end for end. A proper roll cage was present that day, and I was unscathed, apart from cutting my finger on a piece of glass while extricating myself.
No way would a street bar cope with those forces.

So you could say, using a sample of 1 person and 4 rollovers, that street bars are useful in 75% of cases.

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Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, Nevada, USA   USA
Ideally, a roll bar would be frame mounted. This one is at the center.

I've seen ones mounted to sheet metal only that are more decorative than practical.

jhollis Avatar
jhollis Jarrett Hollis
Visalia, California, USA   USA
This roll bar mounts at 6 points - 2 center points bolt through the frame with the remaining 4 points bolted to 4 of the 6 seat belt attachment points, leaving the retractable seat belt in it's original mount position. I'm not sure how much more you can stabilize a rollbar unless you custom make it yourself. This car is more of a daily driver and I don't race it so I am not as concerned about rolling the car. I have always liked the double hoop roll bar and this is the only one that I have seen that is (was) available on the market for purchase. It is a bit short, but if it was higher neither the soft or hard top would fit. As it is designed, both the soft and hard top easily fit with this roll bar.

My original roll bar was the single top bar (as seen in my profile pic) that was bolted to the frame on each side with the center point only bolting to the sheet metal on the "hump". This is one of the designs available on the marketplace. However, I had to have it cut down 2" and narrow the width 2" on each side to be able to close the soft top or add the hard top.

I like the double hoop design much better.
It was originally produced by Performance Research Industries, which no longer exists, but there are guys out there that did not finish their project and sometimes have them available. There are also a number of threads here on PRI. They designed a number of performance upgrades for Spitfires as well as my favorite Roll Bar.

Safety is a relative item when you drive one of these. No air bags, very little separation between you and a spinning drive shaft, an eyeball view of the lug nuts on a semi truck as you pass them, the ability to hide from the view of a semi truck driver - or anyone else on the road - even though you are in plain sight, the ability to barrel down the highway at 75mph in a car about the size of a golf cart... need I say more. Drive safe and defensively, stay off the highway as much as possible, even if you take the more scenic route, slow down for sharp curves and don't test out the suspension as if it is a muscle car. It is not. But the Spitfire is definitely a thrill to drive.

Marcus has the experience of rolling one at 100mph...wow. That's fast, and scary. I am sure that if your plan is to race a Spitfire, then you prepare the car for when it rolls over, not if it might roll over, and your choices for a roll bar or roll cage are different.

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Wolfcreek Steve Steve P
Central, Wisconsin, USA   USA
If you are going to fab your own bar, remember to make the "feet" big enough where fastening to sheetmetal, so they don't pierce the metal. I do like the double hump style as it gives an advantage in upper side impact, as in hitting the ground partially upside down.
Edit: I plan to run no top ,either soft or hard, so my design envelope is a bit more roomy.

I like this design (I believe MGcool smiley and will fab mine similar.



Edited 1 time(s). Last edit at 2017-11-15 12:51 PM by Wolfcreek Steve.


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Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, Nevada, USA   USA
Roll bars make Miata seats more acceptable.

clshore Carter Shore
Beverly Hills, Florida, USA   USA
It's also critical to fit a suitable backing plate when bolting the rollbar feet through sheet metal.
Otherwise, the bolts will simply rip out of the sheet metal.

claytoncnc Avatar
claytoncnc Gold Member Marcus Clayton
Melbourne, Ivanhoe, Australia   AUS
In reply to # 1498022 by jhollis

Marcus has the experience of rolling one at 100mph...wow. That's fast, and scary. I am sure that if your plan is to race a Spitfire, then you prepare the car for when it rolls over, not if it might roll over, and your choices for a roll bar or roll cage are different.

None of the roll overs involved a Spitfire, 3 of them were in a Mazda RX3, including the high speed one.
I used to Race and Rally these extensively in the late 1970s.

The other was an Alfa.

jhollis Avatar
jhollis Jarrett Hollis
Visalia, California, USA   USA
I could see a RX3 being much safer than a Spitfire. Good to know.

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