Members Eric W. Posted March 4, 2011 Members Share Posted March 4, 2011 15.6.12 Door Bars / Side Impact ProtectionAt least one (1) door bar on driver side and one (1) on the passenger side must be used. At least two (2) door bars on the driver side and one (1) door bar on the passenger side must be installed in all vehicles that obtain a new logbook after January 1st, 2007. All vehicles, regardless of date of manufacture or date of logbook issuance will be required to have at least two (2) door bars on the driver side and one (1) door bar on the passenger side starting January 1st, 2011. I have a question regarding this. A handful of racers recently went through annual tech and got a note placed in their logbooks that stated Nascar bars are required as per 2011 CCR. When asked about this, I had no idea, so I looked up the CCR and did not find anywhere that said "NASCAR" bars were required. I asked tech about it and they said until National gave clarification, it was their interpretation that "two door bars" (as emphasized in above quote of CCR) meant "NASCAR bars". I believe this to be incorrect. First of all, it is arguable whether "NASCAR bars" are safer than an X. Secondly, it is my interpretation that an X door bar is actually THREE bars and would satisfy the 2011 CCR. Can someone from national please chime in so I can get our logbooks cleared? Thank you in advance, Eric Quote Link to comment Share on other sites More sharing options...
cstreit911 Posted March 4, 2011 Share Posted March 4, 2011 I diagree with this as well. It is the COMMON interpretation but an X bar is also a double door bar. Look at the WRC rally cars. They use the X brace with appropriate gussets and worry about tumbling into trees and down mountains. I'm not an ME bu several top cage designers have told me that based on their analysis, they are virtually the same. Now I have a NASCAR bar ont eh drivers side and an X ont he passenger side only because I wanted the extra room for the driver. Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 4, 2011 Share Posted March 4, 2011 A handful of racers recently went through annual tech and got a note placed in their logbooks that stated Nascar bars are required as per 2011 CCR. I disagree with this as well. 2 door bars could be: 1. An X-bar layout (whether 1 diagonal bar is a single member and the other diagonal are 2 smaller ones, or a pair of V-bent bars that are tangent and welded to each other in the middle) 2. A pair of straight, horizontal, parallel bars that do not curve outward 3. A pair of NASCAR-style bars that curve outward into the door cavity 4. A single, horizontal bar near the rocker sill with an angled bar from the main hoop mid-point to the bottom of the A-pillar bar 5. A single, horizontal bar near the rocker sill with another single, horizontal bar up near the window sill 6. Any other combination of 2 bars that go from the main hoop to the A-pillar bar Of course, some of the above scenarios are better than others; these are not recommendations, but just examples of installations that would satisfy the "2 bar" rule. It sounds like further training and studying of the CCR could be useful for some cage inspectors. Mark Quote Link to comment Share on other sites More sharing options...
JerryW Posted March 4, 2011 Share Posted March 4, 2011 The GCR's on Page 64 show a typical cage with X-Bars. I'd suggest that indicates X-Bars are acceptable. Quote Link to comment Share on other sites More sharing options...
Members Eric W. Posted March 6, 2011 Author Members Share Posted March 6, 2011 The GCR's on Page 64 show a typical cage with X-Bars. I'd suggest that indicates X-Bars are acceptable. That's what I was thinking too. Was hoping someone from nationals would post something definitive though. Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 6, 2011 Share Posted March 6, 2011 Was hoping someone from nationals would post something definitive though. I am in the process of building a cage for my Mustang, and I have probably done more research on the subject than the subject deserves. Paralysis by analysis... I don't do any national-level tech, but IMO, the CCR are pretty clear about the requirements; just count how many bars are in the door area. If you count 2 or more, then pass. If you count less than 2, then fail. The CCR do not specify minimum or maximum requirements for shape, position, style, or routing of these bars, so I don't see how anybody can enforce their own personal interpretation of it. Of course, some designs are better and more logical than others, so use your best engineering judgment here. FWIW, X-bars that connect the main hoop to the A-pillar bars are considered 2 bars. They could be 2 separate, continuous bars that don't quite touch each other, or they could be 1 continuous bar with a 2-piece, non-continuous bar that are welded together in the middle. I have attempted to call the national HQ telephone number with my cage tech questions in the past, but the answers were less than satisfactory. I would start by contacting the head of your region via email or telephone with this issue (as not everybody reads these forums), as the inspector is in error if he/she is requiring that you install NASCAR-style side bars if the car already meets the 2-bar requirement in the CCR. Of course, there could be more to this story, as the car(s) in question may have had substandard side bars, and the inspector could have been recommending NASCAR-style side bars if the existing ones were going to be cut out, anyway. Do you have any photos of the side bars in question? Mark Quote Link to comment Share on other sites More sharing options...
Members Eric W. Posted March 6, 2011 Author Members Share Posted March 6, 2011 Do you have any photos of the side bars in question? Mark Mark: This is one of them: Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 6, 2011 Share Posted March 6, 2011 Mark: This is one of them: Although I can't see the entire A-pillar bar down to where it meets the floorpan/chassis, I would say that I can see 2 door bars (as long as they both connect to the A-pillar bar), which satisfy the CCR. Result: Pass. Based on what I see of the reinforcing of the upper A-pillar bar (with sheet metal and a dimple die) and the gusset bar that reinforces the upper side bar to the main hoop (adjacent to the driver's helmet), I would say that the cage builder knew what he/she was doing. Mark Quote Link to comment Share on other sites More sharing options...
Members Eric W. Posted March 6, 2011 Author Members Share Posted March 6, 2011 Ive since clarified this w/ Cobetto and all is well Quote Link to comment Share on other sites More sharing options...
edhunter Posted March 9, 2011 Share Posted March 9, 2011 This is not in regards to the legality of an X bar, but more along the safety of one... There is an extensive thread on the corner-carvers site regarding cage construction. A recent post was made regarding the failure of an x-brace in a t-bone accident... Something to be aware of. Just thought I'd share, as my car has x bars on the passenger side. If you're a member and want to read more here's the link... http://www.corner-carvers.com/forums/showthread.php?t=27556 The info below is copied from post #1199 of the above thread... the author is a noted cage builder of road race cars. ________________________________________________________________ The 'X' door bar, without a central gusset, is subject to catastrophic failure with a common type of on track incident: a Tbone to the door historical precedent: http://www.improvedtouring.com/forum...highlight=door this cage failure didn't kill anyone because the impact was on the passenger side, but if the hit was on the drivers side it would have caused severe injuries or worse. No photos, but here is an excerpt of Greg Amy's description: "But post-race we all got a good look at the car. As described the door was completely destroyed, hammered well into the car. The passenger-side rollcage/intrusion protection had completely failed. Richie had the venerable "X" bar on the passenger side, one diagonal tube, with two other tubes welded to that to make an "X". That structure failed. Your first thought is probably that the welds failed, but you would be wrong: all welds seemed to hold. The primarily structural failure was on the first main diagonal bar, which simple tore apart at its center in tension. Then, the two triangular "halves" of the X-bar system hinged inwards where they were welded to the main the front hoops, tearing the two tubes partially off. To imagine this, think of the old Western saloon doors that swing to each side; the X-bar tube separated in the center, then allowed the other car to penetrate in the middle, tearing each half at the vertical tubes they were attached to. The door then came off of its hinges and latches, bending as it penetrated through the "swinging door". The forces of the crash were so hard that the main hoop, front legs, and main plane diagonal bar were bent as well. And lest you think this was some big heavy car, it was a Miata, I believe a SMMAITAC. So, what, 2380#...? " At minimum I would add a broad taco gusset to the top of the X bar junction. A better solution would be to redo the drv door bars with a structure that extends into the door space, giving more elbow room for the driver, and some room for deformation before steel gets to the driver. Quote Link to comment Share on other sites More sharing options...
Members Eric W. Posted March 9, 2011 Author Members Share Posted March 9, 2011 Hard to say from pics but here is another reply from a ME friend of mine: 1) I don't think you can tell anything from the first pic. Could be a lousy weld or undercutting. W/o a close up look, its wild speculation. 2) Just to give an idea of the forces involved to bend a bar: 1020 DOM has ~330MPa yield (before welding) 1.75"x.090" has a section modulus (Z) = 3.04x10^3 mm^3 a single 1.2m long door bar (nascar style) w/ a force in the middle only takes 4*330Mpa*Z/1200mm = 3340N (assuming the bars are free on the ends, but since they're somewhat constrained this is slightly pessimistic) 3340/9.81 = 340kg * 2.2 = 750# (1.5x0.120 only takes 675#) A ~750# point load will cave a nascar bar in. So even w/ two of them, most cars couldn't support their own weight slowly rolling over on a rock. Flat X bars go straight into tension too. I think it should be higher (almost 2:1) because the ends much more closely approximate 'fixed' ends. You'd have to know how much the A & B pillars want to try resisting pulling together to compute. They definitely add the most torsional stiffness to the chassis. AFAIK, all factory GT3 cars use a flat gusseted X. That says something. Pyramid X bars are unique as they go into compression. One could calculate the Euler buckling limit, but somehow I think that would be optimistic. For any load thats off center/off angle it would probably approach the flat X. Though if the pyramid is steep enough, the effective length is reduced driving the force reqd higher. IMO, the pyramid X the strongest of the three. We did it in the gts2 car on the driver side. There is a flat-X on the pass side (no passengers when racing). There is an addl tube on each side from the top of the X @ the B pillar to the C pillar plate to increase strength. Ideally, we'd do the same @ the A-pillar to the front shock towers or something but thats a rule issue in some classes (but not gts.) Whats interesting w/ a pure non-gusseted X: When the tubes go into torsion, there is a weak spot @ the center because it has less cross section. Lower cross section = lower force to reach yield. Gussets increase the cross section of the matl significantly. Note: that # seems somewhat low to me but I've run though the math a couple times. I'll check again when I get to work tom as I have a mathcad doc already that computes this. Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 10, 2011 Share Posted March 10, 2011 Of course, there are a million "legal" ways to skin the roll cage cat. Some are better in crash X, others are better in crash Y. All you can do is hope that you covered your bases, and then crash Z will come along and negate your homework. As for me, I do not like the NASCAR-style bars that use unsupported S-bends at each end. This type of fabrication is mainly used for ease of construction, but I wouldn't necessarily trust it in an impact. If you rotate it 90* and use its shape as a bridge, it suddenly appears to be very inefficient and unstable (and nobody would really design a bridge like that). If anything, these NASCAR-style bars should go outward at a 45* angle where they are attached to the main hoop and A-pillar, while running parallel to the door in the mid-section. I prefer the pyramid-X type of side bars, as is installed on many Porsche factory racers. However, I do not like having a symmetrical pyramid with the intersection occurring in the center of the door opening; I prefer that the intersection (which is also the furthest outboard point) is located in line with the driver's torso, which houses the squishy bits that we are trying to protect. There is a ton of good information in that roll cage thread on Corner-Carvers that is worth reading before diving too much further into a separate cage discussion in this thread (although information that is not already in that thread, such as calculations from an ME, would be nice to see here). Mark Quote Link to comment Share on other sites More sharing options...
kbrew8991 Posted March 10, 2011 Share Posted March 10, 2011 there's a reason we add all this stuff in the first place: Racing is dangerous Quote Link to comment Share on other sites More sharing options...
Members Eric W. Posted March 10, 2011 Author Members Share Posted March 10, 2011 I just got an email from National. They have (or will soon) amend the CCR to say that X bars are legal. Quote Link to comment Share on other sites More sharing options...
racecarbuilders Posted March 10, 2011 Share Posted March 10, 2011 most of the time tech inspectors are just someone that likes to go to the races and will commit to being there. they are payed very little to nothing to be there ..so they get what they get ..i have had issues with new tech guys in the past and had to get ahold of people to get them corrected...it puts a huge shadow of doubt on me to my customers when they do things like this .. his assumption that it meant nascar bars is totally wrong..and it is an assumption.. any two bar in any configuration connecting the main hoop to the a pillar suffices the rule.. any of the following are legal.. you will see i almost always put a bar along the rocker and tie the door bar into it but it isnt required even these simple bars.. Quote Link to comment Share on other sites More sharing options...
National Staff Greg G. Posted March 12, 2011 National Staff Share Posted March 12, 2011 The CCR has been updated. Quote Link to comment Share on other sites More sharing options...
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