Sticker shock

[rficalora]

Went to visit a guy who makes roll cages to get an estimate on a roll bar sort of like this one.  There were a bunch of 4x4's and a couple of drag trucks at the shop and the work they do did look good... but I wasn't prepared for a $750 estimate.  The idea was to have the basic shape of this one but have it tie in at the floor on both sides in three planes (floor board, vertical panel behind the seats, and side of the frame rail).  In the middle it'd attach to the trans tunnel.  And it'd have angled braces going back to the battery shelf and forward to about the middle of the seats (enough to keep it from folding but not so far forward that it'd make it hard to get in or out).  After thinking about it, the price is probably fair considering the fabrication required for all of the places it'd tie into the car but it's still way more than I was prepared to spend.  Plan now is for me to make the brackets and then have Matt (the guy who does the roll cages) just bend the pipe for me.

[roverman]

Rob, If you do the fitting and welding, should save a substantial amount. Local off-road fabricator, quoted me $5./bend. You may want to shop webbsites like S&W Race Cars, for materials and bends. Good Luck, roverman.

[BWA]

Rob what size of pipe and wall thickness is appropiate for a roll bar?  There are no shops here in Calgary that do  mandrell bends, but there is a shop that has a machine that will do fairly smooth bends and they can do tubing up to 1.5" diameter.  I do not know what the wall thickness is.  Is 1.5" diameter tubing big enough for a roll bar?
If this was good enough for a roll bar I would consider getting them to do the bends and then getting my tig welder friend to weld it up for me; his welds are lot prettier than my welds.

Cheers
Byron

[rficalora]

I'm no expert.  NHRA requirements that I saw are below.  My plan is to go with 2" x .118 (or as close as I can get locally) for the main hoops and 1.5 x .118 for the angled braces.  I'm confident 1 3/4 would be fine for the main hoops, but i think the 2" will look better.

If you're thinking of making one, be sure to read up on them.  A roll at that's not done to where it won't fold over on you can be more dangerous than no roll bar at all.  Also, to protect your head it'd have to be pretty tall.  Pull a string from the fender about 6-8" from the headlights to behind the seats.  Angle the string up high enough to clear your head by a few inches.  That will show how high it needs to be to protect you assuming the windshield collapses and the front sheet metal gets bent down an inch or two.   Net is you're not likely to get the sort of protection you'd have in a race car but can get some margin of safety I think.

NHRA rules... A roll bar is required in any convertible running 13.49 seconds or quicker in the quarter mile, and in other cars beginning at 11.49. The roll bar is accepted in vehicles running as quick as 10.00 second e.t., provided the stock firewall and floorboard is intact, other than for installation of wheel tubs. The rollbar must be constructed of minimum 1 ¾ inch o.d. x .118 inch wall mild steel tubing, or 1 ¾ x .083 chrome moly tubing. If the floor and/or firewall has been modified, then a full roll cage is required beginning at a 10.99 e.t. A full roll cage is required in any vehicle running 9.99 seconds or quicker, and any vehicle running 135 mph or faster (regardless of e.t.). The roll cage must be constructed of minimum 1 5/8 o.d.x .118 mild steel tubing, or 1 5/8 x .083 chrome moly tubing.

[Moderator]

Drag racing rule requirements are quite different from road racing. Frankly, I think SCCA's rules make more sense for a street-driven British sports car. The second part of this article includes a summary of them, plus commentary:

http://www.britishv8.org/Articles/Do-It-Yourself-Double-Roll-Hoop.htm

[rficalora]

I'd forgotten about that article but it's a good one.  I still plan to do a dual hoop one, but want to read the SCCA rules to learn a bit more.

[Jim Stabe]

I have provisions for a roll bar in my car and actually had one made up for it but it was ugly and I thought it detracted from the lines of the windshield and the car. What I found from trying lots of shapes is that for the bar to look good it had to be too short to provide any real protection (especially with no helmet) and that made it too close to my head which could result in serious injury if I were hit. The original bar was well braced fore & aft and diagonally and removable and I still have all the mounting points in the car so I could add a functional bar later if circumstances demand one but for now I will make blanking plates that will close the holes in the body and be flush with the surface and (hopefully) will not be that noticable. Having a restriction that prevents me from taking the car out on a road course as fast as the car should be is probably a good thing.

[Jim Stabe]

Rob, and anyone else contemplating a roll bar

Here is some interesting reading on the safety of roll bars for non helmeted passengers. Lots here but worth going through.

http://corner-carvers.com/forums/showthread.php?t=14061

http://corner-carvers.com/forums/showthread.php?t=20586&highlight=street+roll

[MGBV8]

Yeah, I know. Makes me want to remove my roll bar every time I think about it.

Speaking of bolt-in roll bars, anyone think they can actually be made strong enough to really be useful?

[Moderator]

The problem with these discussions is there's such a broad range of installation variables and also such a broad range of accident scenarios. Even the OEMs can't agree on priorities when it comes to safety.

Almost every car on the road weighs more than an MGB, has a higher center of gravity, and is much taller all around... so I figure compared to other drivers we should worry more about being crushed and less about flipping over. I fear being t-boned in an intersection. That's one reason my cage has three extra side-to-side tubes (in addition to the two hoops and the diagonal behind the seats.) It also has bars across the door openings.  Yes, perhaps in a rollover I might crack my skull. On the other hand, I may have the safest MGB on the planet for in-town driving.  (Bonus: extra stiff chassis!)

SCCA has accepted bolt-in cages in Showroom Stock classes for two decades, so apparently bolt-in can be made to work. Can you fit doubler-plates underneath the floor? Can you weld-in mounting plates (under the carpet) and then bolt to them? Almost any car modification can be done well or done poorly.

[tr8todd]

You can use either 1.5X.120 or 1.75X.095 DOM tubing.  You could actually get away with 1.5x.095 or 1.75X .083, but since it's only a roll bar and not a cage, I'd go with the bigger pipe. Either way it will run you at least $5 a foot to buy and it comes in lengths varying from 18' to 21'.  Add another 5 to 10 for each of the steel plates to make the feet.  NHRA doesn't require DOM.  They will let you use the cheaper seam welded pipe, but I wouldn't use it.  Minimum bend radius is 3 times the pipe diameter to avoid kinking the pipe.  Figure out what radius you need the hoop to be and order the pipe accordingly.  One of the big expenses overlooked in cage building is how you deliver the car to the cage builder.  If he has to remove and protect interior pieces, carpet, etc. and then reinstall them, you have to pay him for that time. If it has to conform to SCCA rules, then read the rule book before building.  Make sure the cage builder has the rules or else he'll build what he wants which most likely won't be what the SCCA wants.  The SCCA has rules about minimum bend radius, brace tube angles, max number of bends etc.  I've built a dozen or so SCCA and NHRA cages over the years.  When I go to cruise nights and see what people call cages, I'm mortified.  Filled with useless strength removing bends, incomplete welds, tubes and brackets in danger of shearing in a direct path at the driver. Worst I saw was a 10 second Plymouth K car drag racer that had shoulder belts mounted to a vertical tab on the cross bar.  Incomplete weld would have snapped with a pair of channel locks let alone a person thrust forward under a heavy impact.  Track official said it was cool.  Here is one I recently built for a TR8.  Not SCCA legal because it doesn't have a diagonal and the main hoop isn't all in one plan.  Also it ties into the side which is a no no in SCCA.  This design works great for what I need.  It stiffened up the car substantially and provided a cross bar for my belts that doesn't prevent the seats from reclining fully.  Here is one that I built in an MGB that isn't legal either for similar reasons.

[rficalora]

You guys are slowly convincing me to forego the whole idea... but right now I still want to do one.

[roverman]

One "might" consider the oem roll bars showing up on roadsters these days ? BMW , Porsche roadsters and even Mopar comvertables have them, and have swapped to other vehicles. Cheers, roverman.

[BlownMGB-V8]

I wanted to put one in my RD but I wanted the height to be adjustable and the main hoop to be removable. It got put on hold when the motor needed replaced. But the only reason I wanted it was to be able to drive it on the race tracks. Aside from that in my opinion it is pretty much a bother.

Jim

[tr8todd]

If you take the time and build it right, they really are not that intrusive.  You have to have everything around so you can measure and test fit to make sure they fit.  I have a couple of the TR8 roll bars that are commonly sold on the web.  Both were removed and tossed aside because they fit so poorly.  I built new ones for the cars owners that actually fit and didn't limit seat travel.

[socorob]

The ones in the oem roadsters these days are all called show bars. No rollover protection is implied. They are mainly for looks.

[Moderator]

The ones in the oem roadsters these days are all called show bars. No rollover protection is implied. They are mainly for looks.

Maybe. However, how they're marketed has more to do with our litigious society than with the design and construction of the bars. They could be made to meet the very letter of FIA, SCCA, and NHRA rules and the sales literature still wouldn't promise lifesaving protection because doing so would invite lawsuits.

[roverman]

Not being a structural engineer, I still suspect these so-called , "show bars" are better than "air", in a roll over ? " Mojave Mile" rules will consider some oem. rollover designs, "if" the engineering is provided by entrants. Cheers, roverman.

[HealeyRick]

Another consideration for street bars is the secondary impact of your head and the bar.  In a race car, you're helmeted and belted in with a 5 or 6 point harness, cinched down tight.  Even still, there's going to be some movement during a rollover.  With a standard street bar, you probably will have a 3 point shoulder belt at best and if your bar is low enough to allow the use of a convertible top, your head is extremely likely to smack the bar when you roll.  And don't think that pool noodle insulation wrapped around the bar is going to be sufficient.

[Moderator]

extremely likely to smack the bar when you roll

That argument makes sense on cars which don't have headrests or that have headrests set way too low...  



The B-pillar (i.e. the steel column between door glass and side window) on an MGB GT is further forward than anyone would put a roll hoop. Just to the side of the driver's head! Maybe MGB GT owners should fear their B-pillars.

[BlownMGB-V8]

Any of you guys actually ever been in a rollover? I mean there are a lot of things you can guess about that might happen, plenty of testing with dummies, and even some video but do you really know what happens? Mainly you bounce a lot and stuff goes flying everywhere in impossible directions. That jellybean you dropped under the seat might wind up in your nose for instance. If you are at all conscious when all of this is going on, (and geez, let's hope so) unless you simply panicked at the thought of going one-on-one with the pavement and lost all body function you are NOT going to behave like a crash test dummy. More likely you will have the wheel and maybe the shifter in a death grip. You will see what is happening at least the first time around and fight like hell to get away from it. The second or third time around it's more like a repeating pattern, and in those circumstances you surely hope you can be a quick study. Does that mean you'll avoid hitting your head? Maybe if it doesn't knock you out the first time, or the roof doesn't come in on you. Which can happen. Let's not forget that the motto: "Safety Fast" means taking every possible conceivable action to avoid the accident and that applies inside the car as well as outside. Once control is irrecoverably lost your focus has to shift. It's all about survival, and that improves your odds more than all the padding you can stuff into the car.

But there is this. The windshield on a LBC and especially an MG is worth almost exactly nothing in a rollover. Almost because it may slightly delay the car landing on your head. What you choose to do about that is up to you. I prefer not to drive on that part of the car, but I can see where it could happen. Still, I would much prefer my rollovers to be in something large and protective like an International Travelall. So if I thought a rollover was likely to be a significant part of my future, I guess I'd have to either put a cage in the B or only drive it in parades. And while I do agree that cages and helmets go together remarkably well, It seems pretty unlikely to me that street driving is going to result in my car hitting something so hard that my head goes towards the roll bar at the equivalent of light speed. Then again I never thought a coal truck would run me off the road at 70mph either.

I guess the point is that you have to decide for yourself. Unless you take it on the track and then we have sanctioning bodies taking over some of the choices. I don't like bumping my head though so if a bar is there, I'd think a pool noodle would be the bare minimum. Shirley, there has to be something better. Shirley? Hello?

Jim

[HealeyRick]

Never been in a rollover, thanks, and would prefer not to be.  I saw this video earlier and it really illustrates how much you'll move around in a rollover.  Note how far back the driver's head extends, not to mention his arms flailing around without arm restraints and how nasty the passenger belts can be as well:

<iframe width="420" height="315" src="http://www.youtube.com/embed/e-9XSOM5eIo" frameborder="0" allowfullscreen></iframe>

Bottom line, the single hoop must have helped or he just got lucky as he walked away.

[danmas]

http://www.youtube.com/watch?v=gNAL44D4-bA&feature=youtube_gdata_player

[BlownMGB-V8]

If the rollbar never touches the ground, did it do anything to help?

[Jim Stabe]

I agree. I didn't see the roll bar come in contact with the ground in either of the videos, maybe it was hidden by the dust in the Cobra video. The GT did roll off the top corner of the B pillar a couple times though.