Hey Gene,

I started the thread over on SS. I have asked my local scrutineer this very question and have not yet received a direct answer. I need to know within the next 40 days, or it will cost me $$$ to make changes. I will have a different cage design based on the answer.

CARS seems to have allowed welding of the gusset right up to the intersection - at least that is the way they have it written in the rulebook...

Daniel Buehler Wrote:
-------------------------------------------------------
> Hey Gene,
>
> I started the thread over on SS. I have asked my
> local scrutineer this very question and have not
> yet received a direct answer. I need to know
> within the next 40 days, or it will cost me $$$ to
> make changes. I will have a different cage design
> based on the answer.
>
> CARS seems to have allowed welding of the gusset
> right up to the intersection - at least that is
> the way they have it written in the rulebook...
>
> First rally car, a '94 Subarat is in progress...

Oh, so you started that thread, thanks for doing so.

I think CARS has stated for years that the gussets must not be welded up to the intersection, I know I've seen that in the CARS rule book several years ago. It was explained to me at that time the rule was meant to reflect the Cnotch in the FIA picture but was not written correctly..I don't know just hearsay on this one. Why would your cage design change over inspection holes?

I should clarify what I said earlier. If I just need an inspection hole drilled into the gusset, the design will remain the same. Notches (may) change my design.

My cage builder has a template for door bar gussets in 4-door Imprezas (that's what I'm building). It's a really nice design with four gussets using the traditional 'x' style with the bars (one complete and two halves) in tension. But, If I have to go with the notches, I'll most likely switch to the 'two bent tubes' design. I like the idea of fully welded gussets, no chance of grit, slime and corrosion in the door-x that I'll be stepping over repeatedly.

Do you have any comment on the 'tension' issue raised in Dave Clark's post?

Gene,

How large does the hole need to be? I'm guess a simple 1/4" bit isn't going to work.

Any preference with regards to the location of the hole? towards the V or maybe a little farther back (almost center of the guesset)

---

-Jason

mack73 Wrote:
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> Gene,
>
> How large does the hole need to be? I'm guess a
> simple 1/4" bit isn't going to work.
>
> Any preference with regards to the location of the
> hole? towards the V or maybe a little farther back
> (almost center of the guesset)
>
> 94 Golf
> www.Mack73.com

I really don't like the idea of drilling anything more than the smallest hole that is feasible in the door bar gussets and roof corner gussets for that matter. Gene, here's a suggestion. Maybe invest in one of those video camera probie scopie things like you use for looking inside of engines and what not. I think the Snap On guy was selling them for around $300, you might be able to find one cheaper somewhere else. Then all you would need is like a 3/8" hole at most in a gusset to inspect the welds. THose things work great.

Something like this?

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100608589&N=10000003+10401010

Not that I'm endorsing buying anything at HD...

Not sure how small the scope head is, but I've seen some CARS officials with something that's at least the same brand at events this year.

---

Andrew Steere
Lyndeborough, NH
KB1PJY

Dave , I have one of those new "scopes" and it is way cool. I'll check on the size of a needed hole that allows angling the lead enough.

RA doesn't want to demand holes in all gussets but reserves the right to request inspection holes if the scrutineer suspects a problem. Seems a fair compromise to me.

It might be nice to take pics of the welds pre-gusset to show scrutineers also.

heymagic Wrote:
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> Dave , I have one of those new "scopes" and it is
> way cool. I'll check on the size of a needed hole
> that allows angling the lead enough.
>

> RA doesn't want to demand holes in all gussets but
> reserves the right to request inspection holes if
> the scrutineer suspects a problem. Seems a fair
> compromise to me.
>

That seems reasonable to me.


> It might be nice to take pics of the welds
> pre-gusset to show scrutineers also.
>

That's a good idea. Maybe with the date stamp on the camera so they don't suspect you're just using the same photos over and over again.

Doivi Clarkinen Wrote:
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> Did I miss somewhere in the FIA rules where it
> says there must be holes in the gussets for the
> welds to be inspected? Because I don't remember
> seeing that. Could someone maybe quote that rule
> or post a link, please? I'm not trying to be an
> asshat, I just wanna know if I missed something
> because this is the first I've heard of it. Maybe
> it's a new rule I haven't seen yet.
> In the case of X style door bars made with two V
> bars (as opposed to intersecting bars) I think
> it's a bad idea to have holes because the only
> thing holding the two bars together in a side
> impact is the gusset. There is not enough weld
> contact between where the two bends meet alone to
> hold them together. Mike Hurst likes to go on
> about how Nascar style doorbars are bad because if
> you hit a tree sideways the bars will bend far
> into the cockpit until they are in tension. He
> wants a bar to be in tension to prevent this. Yet
> he favors the two V bent bars for the X style door
> bars. These are not in tension! They will bend
> even farther into the cockpit in a side impact
> with a tree! You are completely relying on the
> gusset to hold those two bars together. That's
> why the gussets I use on that style of door bar
> are the same thickness as the tubing and have no
> holes. If you look at other cages I have done
> with intersecting tubes I have used thinner
> gussets with nice dimpled holes. And if you think
> I'm hiding unwelded tubes underneath closed
> gussets then I just don't know what to say.

Hey Dave,

As Gene notes, the FIA rules spec that the 'bites' out of the corners of the gussets be there. Being a requirement is all that is needed; the reason to do so is not needed to be in the rules. And, anyway, the corner area is the place most likely to be burned through, and adds practically nothing to the function and strength of the gusset. So it does no harm to have them, IMO.

I agree with you in great degree about the double-vee side bar. I advise people to weld a 1/8" thick plate on the inner side of the vee junction, several inches wide (like 4-8" wide), wrapping halfway around the top and bottom of the central vee section, and welded all around. You are quite correct to say that a very large portion of the strength in the joint between the 2 vees is in the gussets; if they or their welds break, the 2 bars are free to rotate inward on the occupant. However, again, leaving a small section of the gusset area open for weld inspection will not have any great effect on the overall weld strength of the gussets between the 2 vees.

Now for my pet peeve on the side bar issue while we we are all batting this around: A single side bar in tension has 2 signficant points of failure that have not been discussed in the posts about side bars: the end welds. When the bar goes in tension upon initial impact, the bar HAS to deflect to take the impact load; this immediately puts uneven tension on the end welds about their circumference. In reality with any serious impact, the side bar will proceed past the state of deflection and into deformation. The uneven-ness of the tension around the welds can become wildly uneven, with the very highest tension forces on the outer side of the weld.

The 2nd best way to reduce this problem is to have double side bars (x or otherwise), for the simple reason of having some chance to spread the loads and thus reduce the individual point loads. The best way (that I can think of at least) is to have multiple side bars interconnected like a NASCAR sidebar set, with the bars bent outwards. The interconnections between bars acts to make the bar set act more like a solid plane, and the outward bends act to place the welds in compression, where they are much more likely to not fail.

Mike Hurst's point is that a SINGLE outwardly bent sidebar is a bad solution, as the bar has the excess length available to bend inward before there is any tension force on the bar to limit this inward bend. But, to your point, a poorly
interconnected x-bar system of any type is also bad.

Regards,
Mark B.

Thanks Mark, good insight on door bars. Speaking of door bars, I think the double X has some function of transfering front strut loading into the rear floor. If a cage isn't connected to the front towers thru the firewall I don't think the X is particulary functional. It's weak point is the near single tube at the center of the X. Also hinders egress in some cars, especially with A pillar supports.

If we're looking strictly at side protection, 2 seperate straight bars should be stronger. One at the sill and one angled down , rear to front. I also like to run a straight sill bar with a V upper bar, gusseted at the common point. This allows easy entry/exit and manual window cranks to work.


For discussion,I wonder if a single door bar outwardly bent in a gutted door is weaker than the factory door beam, which is stamped sheet metal in many cars. The inner sheet metal of a door provides little or no protection, so the outer skin and door beam are it. Maybe an outwardly bent hoop in addition to proper door bars might be better? Yes it would bend but maybe not as bad as tin. The only tension provided in a door is from the striker (held in with two very small bolts), and the hinge mounts. A real bar should offer that much or more. I kind of like Lanes door bars. I remember one of Iorio's Subes with an elaborate "nerf" bar setup built into the sills and floor.