Mark's roll cage question list

I'd say that my roll cage is officially underway and with the very strong possibility of screwing something up, I figured I'd ask now so that you guys can yell at me before hand as apposed to after everything is welded in place....and maybe it will help someone else down the road. When I ask is it legal, I primarily am going for legality from both a NASA and RA standpoint. If it isn't legal in both than it is not desired (i.e. the halo). I have read both sets of rules several times along with the FIA rule set but after a while it all gets mashed together.

Question 1. I'm not planning on doing the door x but is this legal?



Question 2. Is the front A pillar support gusset in that picture legal? It looks like it is just a triangle of sheet metal welded to cover up the open triangle that would be there otherwise.

Question 3. Is there a preference to the orientation of the gussets on the A pillar support bar? I've seen top bottom, back top, bottom front, front back and I'm not sure of the preference of any of them. Does having it opposite the other make it stronger?

Question 4. From what I've read it seems like a door x is better for transitioning force from the front suspension tower to the main hoop. Is it unwise to tie into the front suspension tower if you run the traditional (253-11) sill bar and single door bar? Single bar ok, triangulate those SOBs, or F it get on stage already?

Question 5. When going to the rear suspension tower, should you go to the very top of the tower (like sean did in his merkur) or is it a "just get it close" kind of a thing?

There will be more I'm sure. Thank you all for the help.

I have never seen a door X done that way, but I believe they need to intersect, with one continuous tube. The boxed in area on the a pillar support is not needed, just the gusset the taco gusset.

I personally would do as much in the door opening as you can, that is one area where you are likely to get injured in a big hit, so protect yourself. I opted for the X with an additional sill bar.

I had the cage put in at Izzy's Custom Cages, in St. Louis, MO. I know he does a *lot* of the local RA cages (and some not-so-local), so I'd trust what he did was right. That picture is from my XR4Ti - so if you need any more pics, I can get them for you. Next month, I'm going to have it logbooked, so I can tell ya if it's legal when that happens

Although, according to the RA book:

Door Bars
Structural member(s) connecting to the Main Hoop and Front Hoop in a
straight or 'X' pattern to prevent intrusion from side impact. This
structure is vertically above the sill bar.

I don't see a requirement for an intersection. That boxed in area is a pretty thick plate - I couldn't tell you offhand how thick, but it's serious (serious business?).

Here's what he had to say about it on a bookface posting:

John Huebbe Interesting X design.
May 31, 2011 at 3:47pm · Like

Izzy's Custom Cages, LLC It's how I've done almost all of them when I can. Keeps both tubes as short as possible and uncut.
May 31, 2011 at 5:53pm · Like

John Huebbe Is there any benefit of this method vs. bending both bars?
May 31, 2011 at 8:15pm · Like

Izzy's Custom Cages, LLC Less material to deform and ultimately intrude into the cabin over the 2 bend X and no cuts to fail like the 3 bar X. Another side benefit is that it moves the rear upper bar outward away from the elbow

Officially the door bars are fine and I would have no issues with the gusset as is, and this is for either RA or NRS.

You can tie to the strut towers with any of the door bar configuration. The X bar does provide a path for some of the energy of a strut hit. If you hit hard enough the car will be junk anyway. There is a theory that energy absorption and structure deformation has some benefit. I worry about getting in and out of the car as much as anything, so personally I would do a level sill bar and a sloped single door bar. I really suggest a low sill bar even with a door X.

Rear tower..the bars must be as close to the perimeter as possible. That usually means terminating at or around the rear strut tower. This has a benefit of absorbing loads from the rear suspension if done properly. I usually put a plate on the front of the tower. Top or inside of tower can work also.

I would suggest either taping the bats in place or tacking them and send me pics as you go. You can email or text them. I'll respond pretty quickly .

Gene

mrmagic@olynet.com
360-580-1377

I gusseted the a pillar support bar the opposite of the way you have pictured to allow more area to swing your feet in and out of the car.

Set your seat inside, it made a big difference on mine.

Mark,
The way the side bars are done is actually a very good way. The desired side protection is provided without the weakness of the cut&reweld. I would actually encourage this and not require any gussets; although gussets are good as they spread loads, their main purpose is to prevent the welds at welded tubing intersections from separating. You don't have that issue with 2 complete separate tubes. The downside of 2 separate tubes is the extra side space used up; so it might be a problem in narrow cars.

You are correct on the X and taking loads from the front struts to the main hoop and back of the car. With the sill bar and single sloped side bar, tieing the front strut brace tubes back to the A pillar is OK, but you do risk some bending of the A-pillar verticals in a front impact. You can add a small tube between the A-pillar tube and the A-pillar brace to spread the strut brace tube load. If you ever had an issue at tehc from someone who did not understand or who was an ass, take a hacksaw and cut it out for that event.

There is no real good definition of where the rear barces go in a car. I prefer them to go to the floor for best strutural integity of the cage. If they go to the strut tops, then I would stongly recommend also adding the additional lower bars from the strut top to the lower ends of the main hoop. This triangulates the rear brace area and converts any impact from the front of the cage that is carried to the rear strut tops into more of a vertiaclly downward force. This is better because strut tower structures are made to take VERTICAL forces; they are not so good for longitudinal forces (front-rear forces).

Regards, Mark B. NRS Tech Guy in VA

Thanks everyone for the input. I'd like to specifically thank Gene for letting me pester him for a week. I appreciate it greatly. Thank you for your imput too Mark B. I'm under the understanding that I'm legal and heading in the right direction.

Here are some pictures for others if they want to look.

Here

As far as the back stays go. There are pictures of the original set up and a new "boxed" design. As far as I understand the box is legal even if it might not be optimal. That's ok with me. I'm not going for perfection but rather getting on an actual stage in the relatively near future. Oh and my gussets should have sight holes before they get welded on.

Mark, where's a spreader under the main hoop box. You realise how thin the floor is and youse has a box ON EDGE which may see soome serious force..
Come on!
Where's a tube from base of main hoop rearwards and upwards to the shock mount junction? Not require for the rules but smart for shell life

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Where are we going!

Could you explain that first bit there? Spreader?

And those bars from the main hoop to the towers might get put in but I'm not 100% sure at this point.

Oh, and does anyone in New England know where to find good deals on large alluminum sheets?

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MarkHille
Where are we going!

Could you explain that first bit there? Spreader?

And those bars from the main hoop to the towers might get put in but I'm not 100% sure at this point.

Oh, and does anyone in New England know where to find good deals on large alluminum sheets?

we're all going to hell!

and a spreader is a hunk of plate to spread the forces of a 1250kg car landing on the hoop, moving thru the tubes till they concentrate on the narrow edges of steel resting on the floor which is about 1mm thick
a spreader---or footer, something to disperse the point load..

And just draw the tube in and ponder it..
Then put the damn thing in...should be no doubting its usefulness, it should be self evident.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Rear hoop boxes are ok. Looks like over 50% of the actual plate rests on the sill and the rest of the load is spread pretty well. Idealy you would plate the floor first and then build a box, but many people dont and as long as cage is tied into sills (as yours is) we haven't seen any issues.

I'll concur with Gene. The box is the 'spreader' and connects over half to the sill side, part to the pan and part to the cross strengthening memeber. Only the floor part would benefit any from another spreader and that looks to be in a position to carry maybe 5-10% of the load any way, the sill with take most of it in any hit and the 'box' will really just stablize the flat plate and take a bit of the load. The vertical connections to the sill box and cross strength member are 'spreaders' in themselves.

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john vanlandingham
Where's a tube from base of main hoop rearwards and upwards to the shock mount junction? Not require for the rules but smart for shell life

Why and how?

---

Grant Hughes

Quote
NoCoast

Quote
john vanlandingham
Where's a tube from base of main hoop rearwards and upwards to the shock mount junction? Not require for the rules but smart for shell life

Why and how?

I've said a bazzillion times that everything you do to understand stress to draw arrows..

Sometimes I can't explain too well that which is so self -evident that I can't understand not understanding...

Draw arrows on a photo there going UP which are the nasty forces.
Look.
Open your eyes.
Breathe.
Don't squint, eyes open, relaxed and look at the piccie and the arrow going up.
Now draw the tube from foot of cage to backstay junction---which I would do on the car, not a welded on bar...

Should be obvious.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

I see two other bars from the top of the roll cage holding that strut top pretty firmly in place.
Now I suppose that could bend upward and the rear half of the car could tear off?
Shell longevity? I thought we were supposed to get on stage and rally ASAP and wreck the first car. Those two bars cost $100 for the pair and none of the six customers I've done cages for these past few months have requested it.

---

Grant Hughes