so for all you thread bashers, who have nothing better to do than say stupid shit. shed some light and tell me exactly what is wrong with this hoop. I would like to be enlightend by the pros, who know piping, on how "unsafe" my hoop is. Y8s can you tell me why this is crap? where exactly is the weak point in this bar?. Also why is this bar much more inferior than the ones that are made on a jig and are dom? as far as im concerned. this tubing is far more thicker and stronger than what miatacage has.

In engineering terminology:

You are creating stress concentrations. Whether you sleeve it or not, your main hoop endures bending loads. Sleeves are designed for axial and torsion loads. (EDIT: Sleeves are a BAND-AID used to cover unavoidable joints that endure axial and torsion loads).

Make the main hoop out of one piece. Yours wiiillll bend.

in your opinion, do you think that it is still not going to be strong enough even though there is a solid rod on the inside of the bar that connects the two halves, all welded together so there is no seam, then sleeved?

another question about roll bars/ cages. i dont really know how to explain this. or ask the question, but, comparing my seam which is solid on the inside and sleeved, and comparing another portion of miatacage's cage (where the overhead bars,(the bars that go through the dash and up the a pillar), weld to the main hoop) how strong is that seam? granted it is connected by the area of the dead pedal and connected to the main bar, how strong exactly is it that thoes welds just dont break off and you have this bar come crashing down on your face?

The problem is where the outside bar (sleeve) ends....you are creating a moment about that point (on both sides of sleeve) which will cause failure. It is "stronger" in some directions, but could fail -in dramatic fashion- under the right circumstance.

Consider the outside points of that hoop (which bolt to car) as the end of a lever. You have created a leverage point at that joint which would not be there if it were a seamless piece.

The bends at the sides of the hoop are the failure method for a roll bar. A gradual, mandrel bend with predictable failure which can take a lot of energy and do not break violently until WELL beyond their design range.

That sleeve joint in not only a THIRD failure point, but one which has a poor failure mode. It will take a good deal of force to break, but will not deform in a predictable fashion like the bends. It may bend as little as 10* before it shears in fast fracture failure. This would be bad.

In reality it may not happen, but it's a poor design.

Different stresses, different application.

Those bars tie in two members to form a complete frame, and only see axial loads. There are normally not moments created about those until the frame as a whole has already failed it's designed purpose.

Those sleeves are also necessary for assembly....yours are avoidable...and should be avoided.

Just because you can doesn't mean you should.

thanks for some engineering enlightenment godspeed. i appreciate it

Thanks for listening to reason instead of running off puffy eyed like a lot of the ignorant hard-headed newbs we see around here.

It's one thing to have a bad idea, it's another thing entirely to not listen to the advice of others on how bad that idea is.

Stick around...keep learning...all those guys bashing you on page 1 can help you learn a LOT about making a fast Miata.

heres a visual, made by helen keller and her paper helmet

yeh there are some people, like you who are actually willing to give encouraging advice, other than just straight bashing

that's a little better, and honestly would work...but it's bad practice, and easier to buy a longer bar and bend it.

You have just moved the stress concentrations further out in the main hoop. They will see a smaller moment there, and be less likely to fail...but they are still and will always be BAD.

What is worse if if those points get too close to the bends in you hoop...then you are compounding stress there, and could very easily "rip a corner" off that bar as you're sliding down the highway shiny side down.

i mean split time said he wouldnt let it touch his car. I mean after seeing his car i would have said why even run with a front bumper cover?

yes i did think about this^ when it comes to a roll. i didn't want that bar creating any more stress on the bend and rip clean out so i cut and positioned accordingly

but just to put this out there, where the seam and sleeve are positioned, it is completly solid .

Also consider that all this sleeve-jointing and inside-barring is adding a lot of weight at your roofline, which raises the CG of your car, and will have an effect on handling.

If you think that effect is small then you probably shouldn't own a Miata, or atleast not one modified enough to need a rollbar. I just swapped my carpet, and drove a few weeks sans rollbar and passenger seat, almost every day with the soft top down.

It was a whole different car.

oh yes i know. Hopefully being how low my car is, it can offset this. i have to roll onto 2x4s to get scissor jacks under it

but non the less i will take that and many other things into consideration along this build

It looks like you have plenty of tubing...why don't you just make another single bar hoop?

You could use the tubing from the first hoop you made as support bars.

i will probally end up doing that. or if for some odd reason, i am compelled and feel that this is stronger, then it might stay. Being bashed on or not bashed on, i dont really mind. like i said. its just kinda a way for others to see how to make their own. Depends on them if they do one continous bar, or reinforced to the max bar. but like i said. twice as thick as miata cages tubing. we'll see how it goes, should i ever roll, ill be sure to make a post ,if im still alive.

You should redo the main hoop fasho. I wouldn't want that big ugly sleeve on my bar everytime I walked outside to get in my car.

Also, paint it orange when your done.