Tubing Thickness fo Chassis Cert.

[D. Miles]

I have started on my 65 LeMans tube chassis car, got the floors and firewall all cut out, got the body all level on stands. I bought a 1 5/8 round tube four link strut front suspention kit from ALSTON Race Cars a few years back and I just wanted to know for sure what the minimum tube thickness is for an NHRA chassis certification... Thanks! D. Miles

[D. Miles]

I have started on my 65 LeMans tube chassis car, got the floors and firewall all cut out, got the body all level on stands. I bought a 1 5/8 round tube four link strut front suspention kit from ALSTON Race Cars a few years back and I just wanted to know for sure what the minimum tube thickness is for an NHRA chassis certification... Thanks! D. Miles

[warriors revenge]

what chassis cert. are you looking for???

[all_ryze]

.083 for Chrome Moly
.143 for Mild Steel

[D. Miles]

All_RYZE, do you mean .134? for some reason that's what's stuck in my mind... Kal Schultz, I need a NHRA chassis certification down to 7.50 I guess that would be a super gas cert. Thanks! D. Miles

[all_ryze]

.134 is what I meant! Dyslexic I guess!

[tikiklubracing]

try this

[tikiklubracing]

another

[tikiklubracing]

and this

[69v8tr6]

I built my cage with .120 wall DOM tubing and it passed just fine. When the tech guy looked at the car he measured many spots all on straight tubes for thickness. He also had a whole book full of cage drawings, so it might be a good idea to talk to the certification tech prior to building the car, so you have it built right. The few simple drawings in the nhra book won't be enough for a sub 8.5 car.

[tikiklubracing]

Just use these for reference, or ignore them, who cares. http://forums.performanceyears.com/groupee_common/emoticons/icon_eek.gif

[johnta1]

69v8tr6, was that a IHRA cert?

[69v8tr6]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by johnta1:
69v8tr6, was that a IHRA cert? <HR></BLOCKQUOTE>
It was NHRA cert, I have heard of people having trouble getting a .120 wall to pass, I talked with the steel company and the tubing they had in STOCK was .120 wall but meastured a little thin, they order some new stuff that measured good, right at .120.
The main reason I posted before was to let people know about the SFI cage drawings. I built my car using just the NHRA rule book and had to add a few extra bars to pass tech.

[D. Miles]

Tiki! Thank you very much, I can breathe a little easier now. I went to my shop after work tonight and cut some samples and also found the peices from the bottom of the main hoop, measured them and they were all in the .127 to .135 area. If the minimum was .134 I would have been up the creek. I have the blueprints that I am going by so I'm not too concerned about tube placement although I did have to make some revisions of my own because the kit I bought was for an intermediate car as I first was going to build a 90 Sunbird, the kit was universal for cars with a 95 to 115 inch wheelbase and the Sunbird was 101.5". The blueprints are for a 105" wheelbase, 65 GTO's are around 110" so I had to add a little length to the rear of the frame and add a second rear crossmember one for the 4-link and one for the front framerail hoop as I want the front a little longer to put the fuel cell up there to minimize fuel line (restriction). I have to pick up some batteries for my camera and will post some pics of progess this weekend... Thanks guys! D. Miles

[Brian Baker]

NHRA's minimum wall thickness on mild steel tubing is still .118", nothing has changed. The reason most chassis shops use .134" tubing is because of production variances in the tubing wall thickness. Depending on quality of tubing, a .134" wall tube may measure as thin as .120" in spots, which will still meet certification, but if the same variance was in place on .120" tubing, it would not.

[johnta1]

And if your thickness is .120" and it's bent for the loop it will stretch and possibly be less than .118" which won't pass.
It's safer to have the thicker tubing and not get failed.

[tikiklubracing]

Depends on which certification team member you get, to cert. the bars. Some just sonic test the straights and a few, very few, will sonic the bends, these days. In the old days it was mandatory to check at least one bend. But if everything is oversize he most likely skip that test. They are also strick on welds to the top hoop. Some guys can't weld up there because of the roof. You can have an incomplete weld if you gusset the joint. http://forums.performanceyears.com/groupee_common/emoticons/icon_smile.gif

[jdw_poncho]

Just to add to all the good advice that already been given, If you buy the cheap ERW tubing buy .134 if you buy DOM tubing it will hold the .128 thickness much better.
ERW- Electrically resistive weld
DOM-drawn over mandral

Alot of the manufactures of cages will use the ERW tubing but it will be the .134 because of the differences in the wall thickness. I believe I was told the spec on ERW wall thickness could vary .011". When I bought my DOM, which wasnt that much more than ERW, I believe it came in .125 or .128 cant remember right now. The whole reason I bought DOM was because it doesnt have that weld seam. How much confindence do you have in a piece of tubing covering your head with a seam that could split. DOM can be identified by the black like coating on it and it doesnt have a seam, its as smooth on the inside as the out, not sharp edges to crack when, or if, you turn your car upside down.

[69v8tr6]

I don't think I would go with a .120" again, because of the chance of not passing tech. I did build the car with drawn over mandrel(DOM)
tubing which is seamless and also has a higher carbon content. Many cars are built with 1 1/4" schedule 40 pipe, if you measure the O. D. I would guess it doesn't meet the 1 5/8" spec.

[jdw_poncho]

SCH 40 PIPE! What a deal