TR7 hoop roll bar how to?

[TRip]

Hello everyone, when I have learned how to weld effectively, I would like to design, fabricate and install a double hoop roll bar system for my TR7.  Does anyone have any information about the right way to build one and where it has to mount in the car?

I'd like it serve several purposes.

1. roll over protection
2. structural chassis stiffening
3. side impact protection
4. aesthetic value

It's not intended for race application.  Just general street.

Also, what grade of steel should be used?

I believe that seamless mild steel tubing should be used.  Am I correct?

And be "mandrel" bent.

I'm not too sure I understand what is meant by mandrel bent and how to go about doing that, though.

Thanks

Trip

[WedgeWorks1]

Wow not intended for racing applications with the requirements you have.......thats so not right! Your 3/4 the way there at thsi point with your plan.

[DiDueColpi]

Hey Trip,
Mike's right. You're almost there for a race cage. Check out the SCCA rule book on their  website for roll cage specs and diagrams. Other designs are available but I consider these to be a minimum and a good choice for a street car
Cheers
Fred

[tr8todd]

The problem with the double hoop is the extra weight and difficulty in fabricating.  Each hoop needs to attach on the outer sills, and on top of the tranny tunnel to be effective.  You will also need diagonal down tubes facing rearward to support the main hoop.  When all is said and done, you will blow thru 20 feet of pipe or more.  While the double hoop may look cool, it isn't nearly as safe as a single well designed hoop.  The tubing you should use is called DOM.  That is a fancy way of saying seamless.  You can use cheaper ERW pipe for street apps.  Plan on spending at least $5 a foot for the good pipe and about 10 hours fabrication time to make and install.  There are ready built units available from Kirk Racing Products, but they fit like crap.  I have two of them next to my shop that friends have discarded and had me build better fitting units.  Have to do another one this winter, so soon I'll have three of those things.  A proper SCCA bar will have a diagonal and a cross bar to protect against both rollover and side impact forces.  Drag racing bars usually just have the cross bar.  Here are a couple of pics to show what I mean.  The first picture is one I built in a TR8 that is minimal but very effective.  It doesn't have the diagonal, but it does have a cross bar suitable for mounting belts.  It lines up between the seat top and the headrests.  It is welded in on the rocker tops, the rear parcel shelf and also on the side pillars.  It angles so that it doesn't come in contact with your head or the folding top.  Not built precisely to SCCA specs, but it does the job.  The second picture is a cage in a BMW 200 I recently did.  You can clearly see the continuous diagonal bar and the two piece horizontal bar as well as a small bar for belt mounting all in a single plane.

[77v8]

please make each loop has a rear brace behind it. I have seen them flop over and the guy got killed anyways... If you can go to the track and talk to some people with them installed.

[Bill Young]

Trip, use mild steel DOM (Drawn over Mandrel) tubing. You can check with the SCCA rule book, tubing size and thickness required varies with the weight of the car, but for your purposes I'd suggest at least a .125" wall thickness and no smaller than 1 1/2" OD. Mandrel bending is not required, but the proper type of tube bender that offers the correct support to the tube is needed to get a nice smooth bend without collapsing the tube. In most cases you'd probably need to contact one of the race shops in your area to find someone who could bend the material to your specs. Bending to a tight 180 degree U isn't easy on most benders, so you might have to settle on a modified design using two 90 degree bends with a small flat area between. As already mentioned make sure you install some type of diagonal brace in each hoop and a rear brace as well. As for mounting ideas check out the photos on the Boss Frog web site. http://www.bossfrog.biz/ Note that where the bar mounts to sheet metal the mounting plate is very large and will have a similar plate on the opposite side of the panel.

[roverman]

Trip, "Auto Power" in San Diego, CA. Makes an "approved" single hoop bar. They have been making them for decades. I haven't installed mine yet, so no installation story-yet. Maybe mod a bar from MGB or Jensen Healy / $50. up, in the used market. Good Luck, roverman.

[TRip]

Hello everyone, thank you for the honest reality check.  

I'm definitely not looking for a racing roll cage although I can see how it would start looking like one.  I guess the end result would be similar whether for street or race.

Thanks for all your advice.  

Trip