Way To Check Roll Bar

Simon T.

Simon T.

New member
I have a Miata with a roll bar welded in, the guy I got it from said the bar is SCCA legal (material and size tubing), I WANT to add a front section, and try to make an ITR car. But I want to make sure my bar is good, anyway to tell if it's legal?
 
Look in GCR.

Find minimum thickness and diameter for your car's weight.

Measure diamter, drill test hole and measure wall thickness.

BUT, no Miatae are classed in ITR....so....you mean S? or A? Not that this matters to the allowed tubing sizes.
 
Oh, oops, is it ITU or something? Regional class for cars that are not classified in any other IT class. My car is not legal for SM or ITA
 
No problem. Yes, it will either be in ITO/E or U.

Shouldn't affect cage thickness though. Check the GCR on that for yor car's weight and then check your diameter and wall thickness.
 
How to measure tubing thickness

Simon, to measure the thickness of a tube, drill a small pilot hole. then with the "stick" end of a vernier caliper, measure the depth of the hole when it hits the other side. Then take the "fork" end and measure the outside diameter. Subtract the first measurement from the 2nd, and you get the tubing wall thickness.
 
Sounds like this car doesn't have a log book. Someone please correct me if I'm wrong, but IIRC, to get a log book now the tubing must be DOM, not ERW. Not sure if there's a reliable way to tell the difference.
 
Thanks Tim, I will do that :)

As for it being DOM, that is also a concern, I think he said it's DOM, when I got the car the rules were for DOM only anyway for new cars, so hopefully that's what it is. Worse case I could just sell this bar and get a new cage...:(
 
Simon, if I rember correctly you are a teenage young man.:D < That's good struff. In the future if you have time before buying something ask questions on this site so that you don't end up buying stuff thats' not usable or that's illegal.

Trust me there is plenty of stuff that I look at that I think:shrug:
 
Yes, well I am twenty now, but have been posting here since I was sixteen under a different name I dont know why I can't log in anymore. Simon Tibbett was my old user name (even though that's me! :) ) I got the car to autocross and do PDX stuff, but I just cannot hold back, I HAVE to go wheel to wheel!!!
 
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Eagle7 said:
Sounds like this car doesn't have a log book. Someone please correct me if I'm wrong, but IIRC, to get a log book now the tubing must be DOM, not ERW. Not sure if there's a reliable way to tell the difference.
Click to expand...

The only way I know to tell for sure is to look at the inside with a fiberoptic borescope. I've done that before, but not everyone has access to that kind of gear.
 
Good private garages (non-dealer) with a decent assortment of tools should have a borescope. My son has one, but it is in Bakersfield CA.
 
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Simon,

ERW usually has a seam that you can see and feel running down it's length. DOM should be smooth all around. And be careful drilling the inspection hole. If you hit the inside of the bar when you drill through, you could put the measurement off.

Good luck.
 
A paper clip can be used when you don't have a boroscope...

1st thing to do would be to sand off the paint around the entire tube. If you see a line, you can be 50% sure it's ERW. I've had DOM with an exterior line before, so now it's time to drill your 3/16" inspection hole - on the oposite side of the line. Stick the paper clip end into the hole & feel around. ERW has a pronounced weld seam. You'll know it if you hit it.
 
Just for reference, DOM (Drawn Over Mandrel) tubing *IS* ERW (Electric Resistance Welding) tubing, cold-drawn run through a die or mandrel after the ERW process in order to improve inner surfaces and dimensional (primarily wall) consistency.

Seamless tubing is a whole 'nother animal. CDS (Cold Drawn Seamless) is made from a solid bar that is cold-drawn over a die/mandrel.

The process that Scott describes is valid, as you're looking for any evidence that the welded area at the seam is not consistent. ERW tubing will be slightly different where the rolled strip was welded, whereas DOM will be consistent all the way around.

GA
 
Simon T. said:
Thanks Tim, I will do that :)

As for it being DOM, that is also a concern, I think he said it's DOM, when I got the car the rules were for DOM only anyway for new cars, so hopefully that's what it is. Worse case I could just sell this bar and get a new cage...:(
Click to expand...

Simon,
You should be able to find the type of tubing used (DOM/ERW) in the rollbar by asking the previous owner where he purchased the rollbar from. Call up the vendor and ask them what the material is. The correct tubing size, from the GCR (9.4.F.2), is 1.50 x 0.095.
 
Well I bought the car over a year ago, and don't know how to get in touch with him, the bar was custom made, he said by a guy who does SM cages. It looks good, and the welds look good.

But here is the deal, it did not have a harness bar, and I got one welded on, meaning I have the one that he cut off sitting here, so I have a piece of the tubing off the car with two open ends. So can I just look in it, and look for a weld down the middle? Or is it just a line?
 
If the wall thickness is consistent, and there's no indication of a weld other than visible discoloration, then it's probably DOM.

If, however, you can run your fingers around the inside and you can "feel" where the weld is, it may be ERW.
 
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