Hey all, hope this ain't a repost (I DID skim all the roll cage threads but didn't see too much on this particular issue), but when it comes to roll cages, how important is the DOM vs. regular mild steel tubing issue? I ask my local steel shops about DOM and they give me dumb looks, or tell me it has to be special ordered ($$$$$$$$$$), so if I can go with regular old mild steel tubing I'd be happy. I'm not thinking of racing, I just want something between me and the sheet metal when Dana Durango bumps into me. In some of the posts it says that something is better than nothing, but if non-DOM tubing isn't worthy, I don't want to make a bad situation (no roll bar) worse (dangerous material roll bar). Thoughts?
Thanks for the link. I did read that thread earlier, but it mainly dealt with pipe vs. tube. I certainly wasn't thinking of using pipe, I was concerned with the suitability of the different styles of tubing vs. tubing for my application. From that thread I gathered: "ERW/HREW 1010 grade tube is usually around the same price/lbs as Sch40 blackwall pipe. That means it should be cheaper (or at least, no more expensive) per foot than Sch40 pipe. 1020 DOM tube is stronger still, but double in price. I get 2x.120 HREW for $2.20/ft, and 2x.120 DOM for $5/ft." So basically, ERW tubing is better than pipe, but suckier than DOM. I get that. But what I really need to know, is DOM really that much better, better enough to justify the hassle of getting it, and the over-double cost of ERW?
Just to post experience from out in the world away from theory and drawing boards, I've built many racing cars and had them tested. (not by choice) Several I've been in, and never had a failure, without using DOM tubing. Gone end over end six and a half times, ending up on my roof, and walked away. I'm not saying DOM wouldn't be better, just don't dismiss mild steel tubing as unusable. Unless you're headed for some high speed, heavy duty racing like Daytona, you'll be way ahead of "nothing" with mild steel. Just keep it .090 wall. Hope this helps, Rusty
I think you're getting material and manufacturing process confused. The materials acceptable for NHRA rollcages are 4130 chrome-moly and mild steel. The mild steel is fine for most applications, unless you're planning to go REAL fast. As far as DOM or "seamed" tubing, there is nothing in the rule book about it. I've bought mild steel rollcage kits from Chris Alston's Chassisworks, and Art Morrison. Neither one was DOM. Another thing to think about is that if you use 4130 the cage MUST be TIG welded in. Also the newer rule books say that mild steel must be TIG or MIG welded, so I guess that leaves out stick welding. Larry T Well, I just read your post after I posted this and it looks like you are talking about mild steel. I'd call someone that makes the roll bar kits and see what they say about it.
DOM tubing looks better, but it's still mild steel.... Rusty, as far as keeping it .090 wall, that may be the thing to do with circle track racing, but for drag racing they spec .120, don' they?
Thanks all for the info. Eases my mind a bit I wasn't planning on going 4130, Carroll Smith has me scared to try working with that stuff without plenty of training! And I was probably going to go .120 wall, just because our bender seems to make nicer bends with the thicker wall. Thanks again! I'll be sure to take any pics of the creation, if for no other reason than to say "Do what I say, not what I DO!"
The design of your cage is just as important as the material it's made from. I consider craftsmanship to be a ultimate requirement anyhow. Add some triangulation. I've seen 'square' cages buckle, and honestly that scares me. HREW and CREW makes fine cage material. Use a real tube bender, and either learn to notch with a chopsaw, or invest in a quality tubing notcher (the cheap ones have a lot of deflection) You can purchase bending software pretty cheap, like Bend Tech or EZ Bend where you can model your cage, create an accurate BOM, and lay out your bends to take out the guesswork. Pay attention when welding it up, if you get in a hurry, you can pull a cage out of square and it won't fit worth a damn in your car. My background's in rock crawling, and I've been fortunate not to have been in a nasty roll, just a few flops, but I've watched some guys get in long nasty rolls in the rocks. I've seen cages buckle and bend made of all kinds of materials, I've seen them fail and fold flat too.
HREW is what the majority of cages are made of. I personally don't think that DOM tubing is needed. Just make sure that whatever you pick it will work in the racing class you want to run. I know a guy who built a really nice chromoly (sp?) cage for a road racer and used 1.5" dia tubing which turned out to be illegal in the class he wanted to race (in the wall thickness he used). It isn't hard to pick up a rulebook. Take into consideration that the wall thickness will thin in the bends.
I have built way too many roll cages for circle track and drag racing cars without DOM tubing. If a customer asks for it, or if they bring me a kit with the DOM, I will use it, but for the most part I will use the HREW. I have never seen the HREW fail at a critical joint, and some of my cars have taken some wild rides. The hard part if finding HREW in a wall thickness that will be legal for NHRA competition. I will usually check several joints to find the right thickness as the tubing does vary. Alot of the 1 3/4" HREW comes in .120" wall, which is actually .126", but I have seen it come in at .116" which would not be legal.
NHRA roll bar Mild Steel 1-3/4" dia. X .118 wall. NHRA roll cage Mild Steel 1-5/8" dia. X .118 wall. Chris Alston Chassisworks uses .133" wall for roll bars and cages so it will not 'thin' to less than .118" anywhere, either from manufacturing or bending.Lots of rules about installation, so if you are going to race, get a rule book.
Keep in mind too, that if this is a street car with a cage and you are driving it without helmets and you get into any crash your head will be banging on the cage.
I have seen and driven many rockcrawling rigs using HREW cages. I have rolled more than a few of them over with some rather hard landings. HREW holds up just fine, DOM is not needed in probably 75% of the vehicles that use it.
My own real world testing has shown very little difference in ultimate strength. I have had both crush/deform in violent rollovers. Dom will hold its shape a little better, but not much. The seam on regular hrew has never split on me. I hate to see the seam, so it always goes to the inside of a bend or to the bottom /inside of a visable structure. I have never tested a cage on the street, high/low speed offroad only. I would have no issue building a cage in a modelA out of hrew. 1 1/2 .120wall would be almost overkill on a 2200lbs car. Anything is better than nothing. With a clean halo style cage you could build it to the point that it would be hard to spot from the outside.
shoot, I was going to tell Danny to run 2" .120 wall, but yeah, I think in a car this light 1 5/8 will be fine. We're using a JD2 Model 3 bender and it works REAL nice........
I keep 1.5 in hrew/dom from .095-.219 in the shop. We have a 4" and 6" radius die for 1.5. I only have a 6" die for 1 5/8. The model3 is a nice bender. Been using a Tube Shark for 6years, wish I had one of the newer models, they can bend 3". I have mandrel inserts to do up to 2", but it would make custom mandrel bent exhaust more fun. For the $$$ I will keep butt welding and hand fitting for now.
Thanks to all for the info. Great stuff! The point about a helmet reminded me of something I should have been thinking of, as it is going to be a street car. I was going to pad it of course. Now I just have to decide what's worse, banging my head on sheet metal and whatever piece of the other vehicle hits me, or a padded roll bar. I still think I'd take the padded roll bar, lol. To the bender!
I whole heartedly agree with Blown61 about the roll bar/cage in a street car, padded bars or not. Racing type seats assist the race harness in keeping you well located during an impact. Race harnesses keep you in the seat and away from the cage/bar - something street oriented belts and seats won't do. Helmets keep your head protected from the cage/bar and other near-by objects. Without correctly anchored and worn race belts, seats and a helmet your skull is very susceptible to getting crushed by the cage/bar during a collision. Race car protection can be considered as a "system". Without all of its required peices the incomplete system is more dangerious than nothing at all. Early cars are not crash worthy at todays highway speeds period. Its just one of those risks we all decide to take. Yes, something is better than nothing but just slapping a cage or roll bar in shouldn't be the 'something'. If it were me, I'd design/build a safety cage or a series of reinforced tubes/bars/braces/door braces right into the body cavity area around the passengers behind or as part of the interior panels. If you really want roll-over protection then maybe use a custom bent roll bar (single hoop - well padded) with some triangulating bracing as far away from your head as possible. Good luck with it. -Bigchief.
Drive Em and bobw nailed it... and here's a tid-bit more on the DOM vs EW... With EW, the wall thicknesses do get thin near the weld... so when the NHRA minimum is .118 and you buy .120 or .125, it can be less than .118 in spots and not pass tech for a 9.99 or quicker car. This is why shops like Alston (just bought some this week) use .134 wall tubing... because it is SURE to pass tech. Fast forward to DOM... DOM has a more consistant wall thickness. So, .120 wall DOM is going to meet the .118 NHRA minimum 99% of the time. No need to run the thicker, heavier, .134 wall. Bottom line, DOM will give you a more precise measurement therefore making it possible to use a thinner wall... therefore making it a lighter tube to use. FWIW, I heard that there are some NASCAR teams that actually buy DOM, and turn it (grind it) down to the NASCAR minimum... seems like a lot of time and effort, but they get it as exact as humanly possible. Now... for YOUR application... 1 3/4" EW in a .120 wall thickness will be MORE than adequate. Sam.
Sam, had a chance to talk to a NASCAR chassis fabricator. He told me that they DO reduce the diameter to the minimum. The purpose is to keep the overall weight of the chassis / roll bar cage to a "bare bones" (legal) minimum. Weight is a "parasitic" factor in the design. Extra weight = less speed. (especially out of the corners) On the other hand, our Boneville LSR needs MORE weight! (to counter act wheel slip on the salt surface)
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