Door bars

#1

The regs call out two door bars but say nothing about where in the door opening they must be located. My roll cage guy has tacked them in as shown. Is this going to be legal?

[attachment=1816]IMG00146-20120401-1733_2012-04-02.jpg[/attachment]

#2

That will never fly. Two unsupported bars with no gussets or anything? That the cage builder would even suggest that solution should encourage you to find a better cage builder.

Note in the NASA CCR the cage pic has bars in an X. If you did it that way with big gussets to reinforce the cross point of the X, that would be a minimum safe solution. Minimum. The cage on Old #6 was designed like this and I was kicking around the idea of putting in some additional bars to reinforce the X.

Spend the extra $$ and do this right. NASCAR bars. This is the wrong place to save a few bucks.

#3

I’m not trying to save money here. Just have no idea what’s required. My cage builder is in the drag industry, he has no real experience with road racers. I’ve seen many designs with variations on this theme including NASCAR style, vertical bracing, gusseted X’s etc. No matter how you slice it in an impact both bars will be under tenstion (except real NASCAR designs) and trying to shorten the distance between the main hoop down bar and the front vertical.

The NASCAR bars change this by adding clearance, putting the door bars under compression, and forcing the verticals apart. Probably a much better design overall but I want to go down this path and fix the design problem by avoiding getting t-boned :wink:

#4

[quote=“RRhodes” post=64596]I’m not trying to save money here. Just have no idea what’s required. My cage builder is in the drag industry, he has no real experience with road racers. I’ve seen many designs with variations on this theme including NASCAR style, vertical bracing, gusseted X’s etc. No matter how you slice it in an impact both bars will be under tenstion (except real NASCAR designs) and trying to shorten the distance between the main hoop down bar and the front vertical.

The NASCAR bars change this by adding clearance, putting the door bars under compression, and forcing the verticals apart. Probably a much better design overall but I want to go down this path and fix the design problem by avoiding getting t-boned ;)[/quote]
This is an oversimplification of how the different structures respond to shear and “moment” forces. Any mechanical or civil engineer will agree that an X is far stronger then two bars supported only at the ends. A gusseted X is far stronger than a non-gusseted X. It’s not so much the stiffness at the anchor points because we all have the same number of anchor points. It’s about the stiffness of the structures between the anchor points and their ability to resist t-boning by distributing the load among the X’s 4 beams. Or, in the case of NASCAR bars, turning what would be moment forces into more easily resisted shear and compression.

Useful additional note. Measure the height of your front bumper and use that as a guide on where to make the side bar structure particularly stout.

#5

This:

[attachment=1817]doorbars.JPG[/attachment]

Note that the horizontal bar along the bottom connects the main hoop to the front leg. The vertical bar to the A pillar adds strength (another bar in compression in a side hit). The overlap of the vertical bars means that the joints are in compression as much as shear in the event of an impact.

#6

[quote=“RRhodes” post=64596] but I want to go down this path and fix the design problem by avoiding getting t-boned ;)[/quote] Say another way pls, I’m not sure I understood.

#7

I’d prefer not to use one of the designs that necessitates the removal of the windows and door panels.

#8

How about a modified version something like this?

[attachment=1818]CageDoorBarMods.JPG[/attachment]

#9

[quote=“RRhodes” post=64616]I’d prefer not to use one of the designs that necessitates the removal of the windows and door panels.[/quote]Your priorities are misplaced sir. Most of us have been in at least 1 serious crash. I can’t even crack jokes on this issue. It’s one of those no-shitter don’t turn your kids into orphans issues.

Spend an evening watching crash videos if that will help. There’s a Miata video out there that shows a guy near the front of a pack losing it (got punted) and ending up sideways. His car sustained multiple hits on the side.

A couple yrs ago at Roebling turn 3 in the IFU race, someone (Damien?) ended up sideways on the exit of turn 3. This was lap 1 so the whole crazed IFU pack was 2 and 3 wide at >100mph right behind him. I, sadly, was watching from Flag 4, but that’s how good signature blocks are formed.

What followed was an absolute miracle of SpecE30 cooperation and skill as the entire pack herringboned to left and right into the grass to avoid Damien. It was a goddamned miracle that multiple cars didn’t plow right into him.

If I was in the cage design stage, I’d do sidebars like Jim Pantas did http://www.wildhorsesracing.com/cars/79AIXCar/tn_tn_20111218%20axi%20mustang%20006_sm_sm.html

“I don’t wanna remove my door panels”. Dude, get a grip on yourself.

#10

[quote=“RRhodes” post=64619]How about a modified version something like this?

[attachment=1818]CageDoorBarMods.JPG[/attachment][/quote]
With significant gusseting it would pass tech. But it would still be as meager as possible from a safety standpoint.

#11

How about we compromise and you use a good design on the driver’s side where it matters. Leave the door panel and window on the passenger side (but don’t be surprised to find that bits of glass will find their way everyfuckingwhere if you get dinked in the door - ask me how I know - and they will be rattling out of nooks and crannies for years to come).

#12

I don’t really care so much about removing anything, it’s just that this will be the only thing with four wheels I’ll have for winter so working windows are a plus. And I know from painful experience that my two wheelers are unsuitable for snow and ice, at least with me as the pilot. As to the orphan thing, they’re already out of the house and it beats the hell out of going out in a rocking chair. But I absolutely cannot tolerate being immobile for any reason whatsoever so I get it. “The life you save may be your own.”

#13

Non-sequitur but I had a Fiat in Dallas some genius shot the windows out of. As you said, everyfrickinwhere.

#14

This is a pic of Old#6 from 2007. Note the prominent gussets on the door bars X. This will pass tech but anyone who has been a a real crash will tell you that it’s not really adequate protection. I was considering adding a vertical bar before and after the gusset, before I mooted the issue at RA in Dec.

I’m just repeating myself in post after post so I withdraw from the thread.

#15

Here is mine, if you want to keep the windows this will work. As others have pointed out its not the safest design ever but I assume that risk.

#16

Add “X”, check.
Add gussets, check.
Add verticals at gusset edges, certainly doable.
This will make it a 4 bar design that is non-optimal w.r.t the door shells, and I will leave the bottom bar at bumper height in place too.
I remember your “piece of art” cage well Simon. Now I understand how you came to it.
Thanks to everyone who responded.

#17

I had the same though until I saw a few photos of cars that had been tagged in the door hard.

The extra strength of bars protruding into the door cavity won out over windows.

Ours isn’t quite as stout as Steve’s, but I’m confident that it’s stronger than having the bars on a single plane.


(Right and left sides are the same.)

Before I designed this layout I heard that the lower bar along the door sill contributes significantly to chassis stiffness. I don’t have any data to back that up, but I like having it down there. I also took a hard shot to the rocker at CMP in February that probably would have bent the door frame significantly if that bar hadn’t been there.

#18

Deleted. Wrong forum (again).

#19

Despite what Ranger says, the two bars you show in the first picture would be legal per the rules. Two bars are required. One on the passenger side. I had my cage built by a drag race guy and when I saw the picture that was what first came to mind. They can do very good work but are trying to stiffen the car in different ways. Now even though it would meet the rules, I would not recommend the bars be used this way. A good X is magnitudes better. My car has an X with an additional horizontal bar across the bottom at the rocker and then a vertical bar from the middle of the X to the lower bar. the X is slightly bent to the outside of the car but I am still able to maintain the windows. Each cage design is a compromise. NASCAR bars are better in a Tee Bone situation, X’s are better in a front, rear, or roll over. As a Tech inspector, I could not fail the cage just due to the shown door bars.

#20

Thanks Michael, this is good to hear from a tech inspector. But we have added an ‘X’, gussets, kept the horizontal bar in place, and added a vertical. Granted still suboptimal but much better than the original. I wonder why, if NASA really wants more bracing at the doors, they don’t just require it. It seems like a fairly easy thing to add in the early design stages.