Roll bar questions-yes I've searched plenty over the past two years

[RebekahsZ]

Getting cage built by local builder next week. Was in Birmingham for business so I went by Kirk Racing, which is a cage builder who advertises in lots of racing magazines. The builder there discouraged me from chrome moly (CM). He described some issues with cracking during welding or during strapping cars down during transport, a requirement for tig welding with CM for any future brackets etc that you might want to add later. He also said that even though a cage might not be required for a DE track day, if you have one and it doesn't pass tech, they might not allow you to drive. Although a cage is not required, it could still be a cause for being excluded. Argh! He stated that SCCA does not allow CM cages to be thinner than their DOM steel counterparts, so that any real weight advantage in weight is gained at the cost of a greater chance of failing tech due to tubing thickness. For these reasons, he has stopped doing any CM cages or bars; he no longer has any CM tubing in stock. I do'nt want to do any wheel-to-wheel sanctioned racing, so i was really only concerned about the NHRA rulebook. But if an un-required device can become an inspection item merely by its presence, i guess i cant totally ignore the more conservative rulebook. I think I'm going to go with a DOM steel bar instead of CM. any thoughts/suggestions?

[JMortensen]

DOM is the easy choice. Simpler and less expensive, meets all SCCA/NASA/NHRA guidelines that your car would be subject to.

[Avernier]

im also in Birmingham and build cages. We use dom, and I just did a rollbar in my z. my roll bar would not be something im interested in replicating due to the fact that I sacrificed some safety in order to be able to fit in the car with a roll bar. however, i can certainly fab one up for you if you're interested. just send me a pm and i can send you some photo's of my work, or feel free to stop by and have a look. i currently have two fully caged race 944's here you're welcome to look at.

[WizardBlack]

I will be doing the same thing. It's a lot cheaper as well. I cut an 8-point out of mine to repair floor pans (and the install was crappy) so I can reinstall a cage later. My 8 point cage turned out to be 72 pounds as DOM.

[johnc]

4130 is not required anywhere in NHRA until you get to the pro classes.  Go with DOM.

[RebekahsZ]

I was only going CM to try to save a little weight. I'm gonna follow advice and do DOM-decision made for ALLl the other reasons than weight. I went with shortie headers for practical reasons, this project should be no different. Thanks for the sage advice.

[Snailed]

I prefer TIG welded DOM for pretty much everything. I have done some pro mod chassis and some vintage dragster stuff in 4130 but it seems like it's not very practical for most types of cars even when allowed.

 

There should not ever be any issues with cracking during welding or strapping down a car with 4130. That would make me nervous about the fabricator and his practices.

[RebekahsZ]

Just got off phone with fabricator, he's ordering 1-3/4 DOM on Monday. Trying to get clarification from the area's NHRA chassis certification inspector to find out how far forward the door bar must contact the floor and if any additional bars are allowed for chassis stiffening. At the end of the day, he's the guy I gotta please. My local fabricator who will be building the setup indicated that he was fine with either material and that he is mostly building in CM these days, but that CM must be tigged. I'd rather have a material that can be migged for the addition of window nets and switch panels, etc in the future. I like how you guys have encouraged me to be PRACTICAL. Good advice. Went to a NASA track day as a spectator today. Lots of carnage. I'm thinking of my car more and more as a drag car and autocross car, and less as a track car. I saw more carnage in two hours today at Barber Motorsport Park than I have in two years of drag racing.

 

 

Edited February 16, 2014 by RebekahsZ

[RebekahsZ]

This was Kirk Racing that made the comment about cracking. He sends made-to-order roll bars and ships all over the world. I have been in his shop, seen his tools, jigs, etc. I have no doubt about his fabrication skills. I wonder if maybe he's had a couple of pieces returned, and with high volume sales, I bet he just doesn't want any problems. And we all have problems. I think after hearing the various arguments, I'm down for DOM.

[Avernier]

Thats because nasa runs their events like idiots. They regged 400 people for that event. We typically reg 150 and its much safer.

[RebekahsZ]

I saw the accidents.  They weren't a result of anything organizational.  Just young drivers going too fast in the wrong places.  It was a well organized event, these accidents would have occurred even if the drivers had been completely alone on the track.

[Avernier]

if those people had accidents, its thr fault of the organization at some level, either wrong run group, pressure from other drivers, no instruction when there should have been, something. people don't wreck on track without somebody lapsing. come to a PCA event for a nearly crash free event. or pboc, or chin, or rezoom, or anything other than scca or nasa really.

[johnc]

4130 is medium carbon steel. It's very weldable and doesn't have a cracking issue unless the fabricator goofs up. The number one cause of cracking in 4130 tube fabrication is poor fitments. The gaps must be no thicker then the filler material. That means no gaps greater then .063" EVERYWHERE around the tube junction.

 

A larger gap requires more heat and filler to fill which tends to work harden the joint. 4130 is less ductile then 1018 (DOM) and can crack if a lot of heat and filler is used. 4130 can be MIG welded if the fitments is correct and the welder makes two or three even and smooth passes around the joint. At thicknesses less then .125" post weld stress relief is not required if everything is done properly.

[Avernier]

^^thats good info for sure!!!

[JMortensen]

Just got off phone with fabricator, he's ordering 1-3/4 DOM on Monday. Trying to get clarification from the area's NHRA chassis certification inspector to find out how far forward the door bar must contact the floor and if any additional bars are allowed for chassis stiffening. At the end of the day, he's the guy I gotta please. My local fabricator who will be building the setup indicated that he was fine with either material and that he is mostly building in CM these days, but that CM must be tigged. I'd rather have a material that can be migged for the addition of window nets and switch panels, etc in the future. I like how you guys have encouraged me to be PRACTICAL. Good advice. Went to a NASA track day as a spectator today. Lots of carnage. I'm thinking of my car more and more as a drag car and autocross car, and less as a track car. I saw more carnage in two hours today at Barber Motorsport Park than I have in two years of drag racing.

Why 1.75"?

 

When I was deciding the SCCA had a reg for 1.75 x .120 for roll bars (not a cage, just a bar) on cars my weight. They were also making noises about changing the spec for a full cage at the time. I ended up guessing the wrong way, as they REDUCED the spec at the time from 1.5 x .120 to 1.5 x .095. My 1.75 x .120 6 point cage and driver's door bars are significantly heavier than they needed to be.

 

If I were doing a cage right now I'd go 1.5 x .095. I know you drag race, so if NHRA wants something bigger that's a good reason, but other than that lighter is better. Also if you get into chassis stiffening members and you end up with a 12 point or something like the rest of us crazy idiots, do the stiffening tubes in something lighter weight. Mine are 1.625 x .065.

[RebekahsZ]

It is little wonder there is so much debate and chatter over cages (there are lots of threads that have started innocently enough and devolve into pissing contests over who is a better welder than who). The guy who is a actually doing my 6-pt NHRA bar was happy to do CM, but I backed him down to DOM. I had a salad for lunch, and if I can discipline myself to only eat lettuce for the next six months, the extra weight in the chassis shouldn't matter-maybe I will get faster as the season progresses! Maybe hybridz will become a health and weight loss sight! 1.75 is required for NHRA in a 6-pt bar. Only 1.5 is required for a full 8 or 10-pt cage. My final plan is to really focus on the main hoop this year. Then next year when I pull the dash to do guages, I hope to do a shorter forward hoop at knee level below the dash, then finish out the foot well protection. As a rabid over-thinker, I really struggle to stay on task, and my goal this year is NHRA chassis inspection sticker. So, I best plan is to comply with the rulebook completely, then ask all my questions about gussets, extra bars etc to the guy who will actually be signing off on the car. What I wanted from this thread was help to avoid painting myself into a corner, and I think that has been achieved. The trip to Barber and all the time I spent roaming the pits looking at every bar and cage was super helpful. Learned a lot about fire systems too, which was a subject on which I was totally ignorant. And in the 8th day, God created zip-ties!

[RebekahsZ]

I am scheduled to drop the car off Saturday; the fabricator has ordered 1.75" DOM.  I think my last issue is differential support-I've already torn the floor at the lap joint between the forward floor and the rear floor where the RT mount bolts up.  I am building a cage that is primarily a NHRA 9.99 second "6-point" roll bar.  The required 6 points are the main hoop, rear legs, and door bars.  For lateral diagonal support of the main hoop, most NHRA cages I have seen as examples in the rule book also use two little semi-diagonal legs below the harness bar, and no diagonal above the harness bar.  I'm really not a fan of that design and I really think the SCCA full diagonal is a better design, so I plan to include both a diagonal and the little diagonal legs below the harness bar.  So my last question has to do with differential support.  I can't just put a plate on the top of the tunnel due to placement of my fuel lines and brake lines high in the top of the tunnel, instead, I plan to put plates on either side of the trans tunnel near where the RT mount bolts up.  Please take a look at these options for differential support and vote for your favorite option (or suggest something better).  My car is way beneath the minimum weight for class which is 2800#, so a few extra bars don't scare me.  Plus, I just finished my second day as a vegetarian (I'm starving).

Edited February 18, 2014 by RebekahsZ

[JMortensen]

If you have to do the braces to the diff mount, I'd do option 1 without the bar across the top of the tunnel. 

 

Have you read "Good Calories, Bad Calories" by Taubes? It's a real eye-opener. Been working for me, in 14 months I've lost almost 30 lbs, from 202 to 175. No starvation necessary.

[RebekahsZ]

Thanks Jon. I KNOW what I should eat, but discipline is my problem. Body by pop tart. I'm trying again.