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Stock roll bar (sport bar) strength - 1983 CJ7

I'm looking to get a full roll cage installed in my 83 CJ7 - ideally as an "add-on" to the existing very sound, very solid stock factory roll bar (sport bar).

The tub is also very sound - not rusted at all where the stock bar attaches to the tub behnd the seats and on the wheelhouses

For strength reasons I want to go with DOM tubing for the additional cage portions - rather than using the cheaper - but weaker - HREW (welded) tubing.

One of the shops I talked with said the factory bar was so weak that he wouldn't recommend additng a cage (front & rear) to the stock bar using DOM, but would do the addition using the HREW tubing.

Opinions about using the factory bar as a part of a full cage made of DOM tubing???

BTW - He said he'd be happy to use DOM for a full, custom cage - not using any of the stock bar - but at a considrably higher price.

Yes - I know I shouldn't pinch pennies too much when talking safety stuff - but .....

Thanks

Reply to
lynnhowlyn
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Reply to
L.W.(Bill) Hughes III

DOM tube is drawn from HREW, the drawing work hardens the tube, increases the yield (bending strength) by around 30%. You have to use the strength of materials tables to get the exact numbers but usually you can get close and substitute one diameter bigger HREW for DOM (same wall) or same diameter and one wall thickness bigger.

If you REALLY need a full cage (tough enough for rolling down the mountainside), I'm much more concerned about the mounts and especially the mounting of the cage to the body tub. The factory mounts are way too small to transfer the load to the tub in a seious roll.

So all the BS at the shop comes down to what strength tube to use, DOM will be slightly lighter for the same strength. If you have a good fabrication shop, he won't use DOM, have him use the HREW one size larger.

The other argument you will hear is that "HREW will split at the seam" I'll conceed that DOM is a premium material, much more uniform than HREW. But good quality HREW tube made in a modern tube mill just doesn't have the splitting problem.

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Reply to
RoyJ

I had a CJ with the stock bar in the back and an add on "full cage" in the front. I rolled down a hill one day (about 1 and a half times) and it held up fine. Granted this was at a very slow speed.

Reply to
83 CJ

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