Roll Bar for 73 Blazer

[DevilDog67]

Hi everyone,
I'm looking to get a roll bar installed in my 73 blazer. I understand that for it to be a proper roll bar it needs to be attached to the frame and that's what I'm looking to do.

That said I'm also trying to figure out what diameter the pipe should be in order for it to safely sustain a rollover should that ever happen.

Aesthetically I like the look of roll bars that are thicker in diameter...I've seen some in these forums that are 4 inches or maybe larger in diameter but I believe those are just light bars and are attached to the bed.

Most shops fabricate roll cages and work with smaller diameter piping and my concern is that it's not able to handle a roll over.

For looks I can add padding to increase the diameter of the roll bar so that's not an issue I think.

I also need to find someone in/near Houston that can fabricate it and install it.

Any advice on the diameter and anyone familiar with someone near me that can help?

Thanks

[andrewmp6]

If you want just a normal old school roll bar http://www.offroadltd.com/K5.htm If your going to have one made the size of the tubing don't matter anymore,Its more about the wall thickness and the type of tubing DOM,HREW and ERW.DOM is the strongest and as a price to match it.Then HREW is a step down and last is ERW.As roll bar DOM or HREW would be best.DOM will take a beating and few roll overs,HREW i would replace after a roll over just to be safe.ERW i wouldn't use on anything my life may depend on one day.

[DevilDog67]

Thanks for the great information. I checked out the roll bars at the website but it looks like they're bolt-ins to the truck bed.

I'm hoping to get someone to fabricate one that goes through the bed and attaches to the frame.

I saw this posted on a racing forum regarding roll cages:

Cars over 2500 lbs.
Mild Steel - 1.75" x .095 or 1.50" x .120
Alloy Steel - 1.50" x .095"

Am I correct that the Alloy Steel above is what you refer to as DOM?

Do you know what the two measurements refer to? Is it the tube diameter and thickness?

At this point I'm trying to find someone that can do this in Houston. I'm finding a bunch of guys that do roll cages for racing cars and I'm guessing they'd be able to do it. Getting ready to start calling them today.

Thanks

[andrewmp6]

Alloy steel is another name for ChroMoly and its a step above DOM.In a drag car that could slam a wall doing 150mph+ you want the ChroMoly.Most rock bouncers and tube buggies are made out of DOM and they take a beating just fine.On the 1.50x.095 the 1.50 is the tubing diameter in inches.The 0.95 is the wall thickness of the tubing.

[special-K]

Race vehicles mount roll bars/cages directly to the frame. Road vehicles you need to fab brackets under the floor mount that link to frame. That's how you keep from cutting big holes through your frame. You'll want the 1.75 - 2" tube. Larger is not only overkill but will present clearance issues and be extremely hard to work with. If you decide you'd like to pad the bars (if interior) you'll want the smaller pipe. It works just fine, always has.

[DevilDog67]

Awesome information thanks guys.

[Mike C]

Just to add a little to the other guys comments, DOM is drawn over mandrel meaning they pull an oversize "ball" (the mandrel) through the tube when it's made to strengthen the seam. The CroMo tube will also be DOM. The DOM basically starts as HREW steel but undergoes several more processes including the mandrel draw that strengthens it. And about doubles the price per linear foot.

[ryanroo]

the drawing process includes dies on the outer diameter as well as the mandrel for the ID. a513 DOM (the stuff you will be using for a roll cage) is just a513 ERW (ElectricResistanceWelded) tube. HREW is ERW tube. it is just hot rolled material. CREW would be the cold rolled counterpart. the only difference is material finish. the post process of cold drawing DOM through the dies/over the mandrel cold work hardens the steel. this gives you the additional yield and tensile strength and obviously makes the material harder. these sound like good things, but it depends on your usage. it also gives a better surface finish on both hot rolled and cold rolled tube. as well as making the tube more concentric and dimensionaly accurate.

i like to use DOM in roll cages and rock sliders. it really depends on what it will be doing. the work hardening helps relieve the stress of the welding, and in certain circumstances that the tube will see twisting forces, helps keep the integrity of the seam intact. rock sliders, because the surface hardness (rockwell hardness) is greater and can handle being dragged over stuff without gouging as severely. since DOM is harder due to its cold working, it looses some ductility. that will lead to cracks in a member that sees more flexing under load. so if you are planning on something that will see cyclic elastic deformation, it may crack sooner. this applies to CrMo even more.

CrMo was mentioned and labeled "alloy steel". that is a little misleading. CrMo is alloy steel. but all steel is an alloy. DOM, ERW, and CrMo are all alloy steel. CrMo just has Chromium and Molybdenum alloyed as well. the advantage to CrMo is the increased tensile and yield strength as well as hardness. it is used because these properties allow a thinner wall tube to support the same load as a thicker walled carbon steel. thinner wall is lighter. there is no advantage to CrMo in a basic safety cage. in fact, it requires a little more expertise to weld not to mention it is notably more costly...

I built the cage in my M715 from 1.75" x .120" wall DOM. i would have no issues trusting a cage properly built from ERW tube as well. i like DOM for the additional strength properties, but mostly it is easier to order one kind of tube and use it rather than try to sort out the high abrasion areas and remember what stick of tube goes where. DOM is also handy because the drawing process removes the flash from the welded seam and it is dimensionaly accurate so you can sleeve tube over tube or use it as a bushing or pivot in other projects.

2" is the max diameter you will likely be able to use in your cage. most shops that do that kind of work use benders that only accept tube up to 2". i would also consider it to be a step down in overall durability as the tube gets bigger. it is easier to deform a bigger diameter with a high concentrated load. i.e. in a rollover if the cage hits a pointed rock and it dings the tube, it looses a lot of its resistance to plastic deformation. so, while i have no advice on your local shops i recommend a 1.75" or 2" diameter .120 wall cage constructed of ERW or DOM. this will likely be the suggestion you get from any reputable shop that does that kind of work.

[DevilDog67]

Thanks for the great information.

Ryanroo,
Does all that also apply to a roll bar?

If not what would you recommend for a roll bar? I'm looking to have a roll bar fabricated that will attach to the frame of the truck.

I don't plan to go rock climbing...I'm more concerned with the fact that my '73 does not have a cab and I imagine that with the higher center of gravity a roll over has a higher possibility. So I'm just trying to make it as safe as possible. Here's the kind of roll bar I'd like:

[ryanroo]

Yes, all the same for a roll bar vs a cage.

if i was going to the trouble of doing a bar as pictured, i would pony up for a little more tube and few more hours and have the shop run some a pillar tubes and make it a cage. a roll bar is definitely a step up from nothing, but a cage could be the difference between a bunch of stitches in your noggin and no real damage if the truck goes belly up. this also adds the opportunity to mount the seats and seat belts to the cage, so if you do have a bad turn of luck, you, your seat and seat belt are all tied firmly to the safety structure. that is another level of involvement, and if i was doing a street rig and just going for safety i dont think i would take it that far.

another thing to consider if you are going to connect the bar/cage to the frame is the current state of your body bushings. i would make sure they are new and polyurethane. the frame connections to the bar should be mounted on some form of bushing, the most likely candidate will be poly t-bushings. they will essentially act as additional body mounts. if the current mounts are old and smooshed, if you ever go to replace them after the shop builds the bar, nothing will fit the same as it should. also, given the likelihood that the bar will tie to the frame via poly bushings, you will want to match that so the body bushings dont start to wimp out over time while the poly bar mounts are still sturdy. that will create a bind and a lot of stress on the sheet metal where the bar to frame tie ins are.