Roll cage tubing size

#1

Since a couple buddies offered to go in on a tubing bender with me, I’m on the fence again regarding buying a used bolt in cage. Now I’m thinking of building my own cage.

What size roll cage tubing are you guys running?

According to the NASA CCR, a car with a weight bewteen 2201 and 3000lbs (such as a Spec E30) must use at a minimum 1.5x.120 wall or 1.75x.095 wall tubing. 1.5x.120 is about 1.77lbs/ft and 1.75x.095 is about 1.68lbs/ft. I would love to use the heavier 1.5" tubing for clearance and reduced bending radius. From what I’ve read here and on the old mailing list, it appears that most people have no problem getting down to minimum weight. Unless I’m using several hundred feet of tubing, I assume I can ignore the single digit weight penalty of 1.5x.120 tubing. The additional bending strength of 1.75x.095 is definitely something to consider. According to my very dusty memories of my solid mechanics class, the 1.75" tubing will provide a 36% increase in bending strength over the 1.5" stuff. Is this something I should worry about or am I overly concerned, especially since I will run a bolt-in cage if I don’t get the bender?

Ed

#2

EdW wrote:

[quote]Since a couple buddies offered to go in on a tubing bender with me, I’m on the fence again regarding buying a used bolt in cage. Now I’m thinking of building my own cage.

What size roll cage tubing are you guys running?

According to the NASA CCR, a car with a weight bewteen 2201 and 3000lbs (such as a Spec E30) must use at a minimum 1.5x.120 wall or 1.75x.095 wall tubing. 1.5x.120 is about 1.77lbs/ft and 1.75x.095 is about 1.68lbs/ft. I would love to use the heavier 1.5" tubing for clearance and reduced bending radius. From what I’ve read here and on the old mailing list, it appears that most people have no problem getting down to minimum weight. Unless I’m using several hundred feet of tubing, I assume I can ignore the single digit weight penalty of 1.5x.120 tubing. The additional bending strength of 1.75x.095 is definitely something to consider. According to my very dusty memories of my solid mechanics class, the 1.75" tubing will provide a 36% increase in bending strength over the 1.5" stuff. Is this something I should worry about or am I overly concerned, especially since I will run a bolt-in cage if I don’t get the bender?

Ed[/quote]

Ed, we have all of our cages done by Mark McMahon in Akron, OH. He has some specs of the tubing on his site:

http://www.rollcageguy.com

I don’t recall mechanics of materials very well either but for me, I’d go with the higher strength. Of course if you can do a FE model then you’ll know the real effects. ; ) I had 1.75x.095 in my previous car and in my current car, visibility has never been an issue. Best thing is to have it done properly by someone skilled, then the tubes will not interfere with line of sight. If you go with bolt in, which I HIGHLY RECOMMEND AGAINST for many reasons, I would definitely go with the higher strength tube. Safety first!

Jack Money
Elephant Motorsports
www.elephantmotorsports.com

  • SpecE30 Supporting Vendor *

    Post edited by: Elephant1, at: 2005/10/26 14:02
#3

We used 1.75x.095 on the two Salazar coupes (Alex’s has 1.5).
The 1.75 stuff is lighter and stiffer, so it was a no brainer for Vic and I.
Bending 1.75 is not hard at all, just use a long enough bar (5-6 ft) to the bender.

http://www.pbase.com/victorhall/image/37772512

For reference, we used about 80 ft of steel tubing for each car.

Here’s a gallery of my cage building project:

http://www.pbase.com/han_ahsue/spece30_project

Han

#4

Cool pics. What’s the trick to getting into the front footwell area to weld in the doorbar and 7th point bars?

#5

That web site should be stickied. I spent nearly an hour scouring over the pics.

A great resource for those of us who are still in the planning building phase with limited budgets.

#6

What about mixing tube sizes as long as all the main tubes meet the spec? I used 1.75x.120 for the main hoop and rear legs for strength in my old track car and planned on using 1.75x.095 or 1.5x.120 up front to save on weight. A quick scan of section 15.6 of the CCR did not turn up anything forbidding it.

As of right now, I’m leaning towards 1.75x.120 for the main hoop and back and 1.5x.120 forward of the main hoop for clearance.

What do you guys do for gussets? Wrap around sheetmetal seems to be the current rage and is probably the strongest way to go.

Flat gussets along the tube centerlines are popular amongst the roundy round dirt track guys and some still use more conventional tube "kickers" in smaller diameters (1").

Tube gussets:

Some of my previous work, both 4 point bars:
An old track car - http://bucktownspeedshop.com/gallery/e28_rollbar
A friend’s Mustang track car - http://bucktownspeedshop.com/gallery/connectors

#7

In the top photo above, it looks like the cage bars are welded to the door opening. Is this a Spec E30 car?

I haven’t looked at the NASA regs on cages, lately.

Is this legal?

Carter

#8

That’s not NASA legal. Also, I believe that the door had to have been gutted and cut to accomodate the door bars which isn’t legal since it isn’t a NASCAR style doorbar.

#9

Carter wrote:

[quote]In the top photo above, it looks like the cage bars are welded to the door opening. Is this a Spec E30 car?

I haven’t looked at the NASA regs on cages, lately.

Is this legal?

Carter[/quote]

The silver car is a VW Jetta of some sort, World Challenge or Grand Am. Welding to the car there is not legal.