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Roll Cage Questions

65AFX

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Installing an S & W 1-5/8 X .134" MS roll cage kit in my 65 Coronet The kit came with 1-5/8 tubing for everything.
1) Can I replace the main hoop cross bar with 1-1/4 X .125"
2) Can I replace the "D" bar legs with 1-1/4
3) I want to add a dash bar. Can I use the 1-1/4"
4) What size tubing do I use for the front frame supports. (1-1/4") Thats the bar that will run from the dash bar, thru the firewall, over the shock tower and bend down to the top of the frame rail.
 
Check NHRA rules carefully. I had problems[with a cert] with the tubing size for my rear driveshaft loop. It was all moly/pro-built, chassis car.....just older.

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Installing an S & W 1-5/8 X .134" MS roll cage kit in my 65 Coronet The kit came with 1-5/8 tubing for everything.
1) Can I replace the main hoop cross bar with 1-1/4 X .125"
2) Can I replace the "D" bar legs with 1-1/4
3) I want to add a dash bar. Can I use the 1-1/4"
4) What size tubing do I use for the front frame supports. (1-1/4") Thats the bar that will run from the dash bar, thru the firewall, over the shock tower and bend down to the top of the frame rail.

If you plan on racing this, check the rules on the class you are going to be in. They mandate the tubing size and thickness. If you're doing it just for looks(yeah, some people do) then i would still want to go by the rules for the size and thickness. Simply because of strength.

Just curious, why you want to go with smaller diameter tubing.
Well, if he's racing and as access to a good TIG welder, most sanctioning bodies allow for a smaller diameter and thickness IF, a big IF, the tube material is Chromemoly Steel. Going one size smaller and a tiny bit thinner wall CAN save you some weight in the change, especially if its a full cage.
 
I didn't realizes how heavy the MS tubing was. So I want to try and drop off some weight. I remember reading somewhere that the smaller tubing I referenced was legal for NHRA, but I want to confirm. Going with CM would have been a big job. I can't weld CM. All I can find on NHRA rules is their reference to SFI specs. So hoping someone has access to the SPI spec.
 
I didn't realizes how heavy the MS tubing was. So I want to try and drop off some weight. I remember reading somewhere that the smaller tubing I referenced was legal for NHRA, but I want to confirm. Going with CM would have been a big job. I can't weld CM. All I can find on NHRA rules is their reference to SFI specs. So hoping someone has access to the SPI spec.

This is off Page 28, 2019 NHRA Rule book for full body cars.

upload_2019-7-3_9-40-39.png


View attachment 793535
 
I didn't realizes how heavy the MS tubing was. So I want to try and drop off some weight. I remember reading somewhere that the smaller tubing I referenced was legal for NHRA, but I want to confirm. Going with CM would have been a big job. I can't weld CM. All I can find on NHRA rules is their reference to SFI specs. So hoping someone has access to the SPI spec.
you can get the whole rule book here.

http://promod.nhra.com/userfiles/file/Tech/2019 General Regulations.pdf

Full body cars start on Page 28 for roll cages. Page 29 talks about some other good useful information
 
Great, just what I needed. But I didn't see anything on the front end frame support. That's the one that goes between the dash bar and front frame rail just in front of the shock tower.
tube
 
Great, just what I needed. But I didn't see anything on the front end frame support. That's the one that goes between the dash bar and front frame rail just in front of the shock tower.
tube
I'll pull it back up, there's a line in the rule book that states dash bars and all cage support bars have to be 1.25 x .118 MS or 1.25 x .083 CM to match the rest of the cage.
 
I didn't realizes how heavy the MS tubing was. So I want to try and drop off some weight. I remember reading somewhere that the smaller tubing I referenced was legal for NHRA, but I want to confirm. Going with CM would have been a big job. I can't weld CM. All I can find on NHRA rules is their reference to SFI specs. So hoping someone has access to the SPI spec.
Actually, same size tube in both MS and Mild is the same. The weight difference comes from being able to use a smaller size MS tube vs the rules saying you have to use larger tube when using Mild Steel tube.
 
Actually, same size tube in both MS and Mild is the same. The weight difference comes from being able to use a smaller size MS tube vs the rules saying you have to use larger tube when using Mild Steel tube.
Um... MS=Mild Steel... CM=ChromeMoly....
 
You'll notice that the min for MS is .118". However ELW tube wont pass this spec unless its .134". However DOM .120" will pass. It can be Mig welded. The cost is more, nearly the same as CM. The nose bars have no spec as they arent considered necessary by NHRA. I used 1.25".
Doug
 
Thanks to all. I got it all figured out. I read the rules on the link that dukeboy_318 sent referenced.
 
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