Elan Rollbar Design For Trackday Use

[type26owner]

Planning on using 2"OD x .13"Wall DOM steel tubing for the main hoop but haven't any resources which list the midplane radius for the typical mandrel tubing bender. Anyone know that value for 2" and 1.5" tubing? Using current SCCA criteria for the rollbar strenghts in each designated direction as the baseline. The only real guess work is predicting the tearout strenghts of the typical Elan chassis bobbins and mounting points. Anyone know those values by chance?

The commercial units are a joke at the height with which they typically extend up unless you are only 5' tall. At 6'2" none of the premade units are acceptable I've determined. Anyone wearing shoulder harnesses will be in harm's way. Mine is going to extend 2 inches above my helmet or 20" above the bodywork and to accomplish this I've thought of a way to construct it so the regular hood (softtop) can be slightly modified to fit through the hoop and still be somewhat water-tight. This design is not completed and the FEA has not been done yet. Just realized how to do this in a simple way while motoring into work yesterday.

Has anyone tried these seat belts with the trick switch activated inertial mechanism for the shoulder harnesses? <a href='http://www.autotech.com/autocntrl.htm' target='_blank'>http://www.autotech.com/autocntrl.htm</a> Are they worth the extra cost?
Keith :blink:

[LotuSport]

Hi, Keith -

I had a rollbar custom-made for my Elan ('70 S.4 SE DHC) that meets your criteria and is an elegant solution. I'm 6'-3"+ and 200+ lbs, so a rollbar height that will protect me is critical. I don't have specs or other criteria (mine was done by a pro who serves local SCCA and vintage racers), but my only stipulation on his design/fitment other than safety was to match exactly the height and curvature of the rear top bow (so I can use it to properly substitute for the top bow on the rare occasion that I have to erect the top -- it's a perfect fit).

I have a surprising amount of headroom in the car with the top up, and I measured a clearance of nearly two inches above my head to the top of the rear bow. My fabricator is an artisan and craftsman of uncommon talent, and he not only met my request perfectly, but he mounted the completed, triangulated rollbar solidly to chassis at six points. You can see the pics of my car with this bar on the Yahoo! Groups Lotus Elan List site in the Photos Section. Look at: <a href='http://photos.groups.yahoo.com/group/lotuselan/lst?.dir=/Bob+M%27s+%2770+S.4+SE&.src=gr&.order=&.view=t&.done=http%3a//briefcase.yahoo.com/' target='_blank'>http://photos.groups.yahoo.com/group/lotus...case.yahoo.com/</a>
…and the fourth pic “Quality…”

Hope this gives you some useful ideas. Notice that this is a stout roll bar and that the bends are large-radius. BTW, I didn’t ask my fabricator, but I’ve been told that mandrel bending has been largely superceded by wet-sand-packing the tubing and bending ‘round a properly sized form.

Best regards,
Bob
[email protected]

[type26owner]

Bob,
That's the nicest rollbar installation I've seen yet. I'm going to borrow the curvature of the top of the hoop because it's very pleasing to the eye.

It's just not quite tall enough to make me totally comfortable wearing shoulder harnesses though. Years ago I had the foresight to add a substantial attachment bracket to the chassis where it splays out to the strut towers when I did the standard chassis stiffening modifications. With this bracket I've won't need to attach the lap belt attachment points which intuitively seems to be a better way to go. Had the bright idea if the forces acting on the rollbar bend it then it should be designed to actually deform slightly and make contact immediately onto other places which can spread the load substantially. The final design is still only an idea and nothing more. 3D modeled four variations already on how I'm not going to do it though. I'll share the design when it's done.

Thanks,
Keith