Roll cage design for review and comments

[TurboShortBus]

This post is mainly intended for Al, Glenn, or other directors to answer or discuss. This comes from somewhat of a cage discussion at another thread:

http://www.camaromustangchallenge.com/forum/viewtopic.php?t=3568

 

I have also posted several photos of the evolution of this design in the "Cage Design" thread on Corner-Carvers.com, which some of you have already seen.

 

Here is a cheesy diagram of the cage layout that I am strongly considering. Green = chassis floorpan/firewall and helmet, while red = roll cage bars. Ignore the setback driver location as shown, as it was determined in the above post (and my friendly telephone conversation with Glenn) that such construction, while some may interpret it as fitting into a gray area, is not permitted in CMC and future rules revisions will reflect that. No problems there.

 

 

While this cage diagram would accommodate a setback driver location, it doesn't mean that the driver can't stay in the stock location. I have found no maximum fore/aft dimension between hoop and helmet in the CCR, so I don't foresee a problem with leaving the hoop where shown and the driver in the stock location. It is my interpretation that this would be legal for CMC competition, as well as being able to take advantage of more liberal AI or TT rules in the future, if desired. However, as I mentioned in the thread above, this construction could conceivably allow me to mount my maximum 150 lbs of ballast nearly a foot further back than other cars (it can be no further back than the plane of the main hoop), but to be honest, this car is a porker right now (3260 lbs with driver, sans cage) and there is no need for ballast, so that's not even a consideration for me, although it could be for others.

 

There are only 6 typical chassis mount/contact points with this layout (hoop, rear kickers, and A-pillars). There will eventually be 2 more chassis mount points, either at the front wheelwells or firewall, for footwell protection bars (as permitted by the CCR).

 

As shown in the diagram, the vertical red line that extends below the green floorpan line is located at the 60/40 balance point of the car and would serve as a jacking pad that is tied into the cage, and will be no lower than the OEM jacking pinch weld. It would be made of 1 3/4" tubing and would pass through a 2" hole (or larger) in the floorpan, making no contact with any other steel chassis member. I would probably seal the hole with silicone or fire-resistant caulk. This bar continues up to reinforce the A-pillar, approximately 3/4 up the windshield, NASCAR-style. This makes more sense to me than an FIA bar.

 

The rocker sill bar, as shown, will pass through the sheetmetal crosspiece that is behind the front seats (it also holds the clips that retain the back seat cushion). There is a large existing hole in the front plane of this crosspiece, but another one will have to be cut in the rear plane for the rocker sill bar to pass through. As with before, a 2" hole (or larger) will be made for the 1 3/4" tubing, and the tubing will not touch this crosspiece.

 

The side bar configuration would form more of a truss than a typical X or NASCAR-style ladder bar layout. There are at least 2 side bars, so this satisfies the CCR. The upper horizontal bar would bend outward to provide additional side protection.

 

The slightly angled, vertical bar next to the helmet (as drawn) would attach to the side bar at its furthest outboard point to help with side protection. It would attach to the overhead halo several inches in front of the main hoop in order to provide additional support for the welded halo-hoop connection (HAZ).

 

Al, Glenn, and other directors: Is there anything about this layout that is contrary to the CMC rules?

 

Thanks in advance,

Mark

[cmc35]

Mark,

 

Great post, thanks for getting this out there.

 

Are you planning to put NASCAR bars in the driver's door? It looks like only a diagonal; if that's the case, then I think you have to keep the OEM crash bar in the door, plus you need to leave most of the sheet metal on the door. Those crash bars are stupid heavy.

 

I'm sure there will be more comments/suggestions/etc. Keep a thick skin.

 

-chris

[TurboShortBus]

Well, the side bars will curve somewhat outward, but not completely into the door (NASCAR-style) since the car still has the glass and PW regulators in the doors. The OEM side impact bars will remain as well. This car sleeps outside, so I need to keep it water and bug resistant.

 

A thick skin, here? This is child's play compared to Corner-Carvers! Besides, Glenn and I yapped for about 45 minutes on the phone a few nights ago, and everything's cool.

 

Mark

[DrC]

I plan to have three door bars where 2 will look like the center example and then a straight bar on the bottom. I am going with three bars because I have been hearing that sometime in the future three bars will be required and now is a better time then later to install it.

Also if I plan to change classes it may be requires. Is my thinking correct or am I smoking some cheap stuff then affecting my reasoning?

Currently I hope to run CMC later this year

[Al F.]

Mark, there are a couple of things on there we'll need to chew on. Give me some time.

 

Dan, I cant remember any time where NASA has changed cage requirements but did not grandfather cars with existing log books for some tremendous amount of time.

[TurboShortBus]

No problem, Al. I don't plan to fire up the MIG for another couple of weeks.

 

Mark

[cozog1548534733]

As someone who is soon going to have the cage fabbed in the car, should I wait a bit to get this done? Are the cage rules for CMC going to be modified any time soon? Just checking...

[jeffburch]

As someone who is soon going to have the cage fabbed in the car, should I wait a bit to get this done? Are the cage rules for CMC going to be modified any time soon? Just checking...

 

No rules creep perceived in this area.

Git-r-done.

jb

[Glenn]

As someone who is soon going to have the cage fabbed in the car, should I wait a bit to get this done? Are the cage rules for CMC going to be modified any time soon? Just checking...

 

The Directors want to find a way to prevent what is being done here - moving the driver back to move weight back. We just haven't found a way to do it.

 

Build the cage according tot he CCR. Focus on quality of fabrication and not exploitation of the rules.

[CMC#11]

Focus on quality of fabrication and not exploitation of the rules.

Agreed, that is for AI not CMC.

[TurboShortBus]

The Directors want to find a way to prevent what is being done here - moving the driver back to move weight back. We just haven't found a way to do it.

 

Build the cage according tot he CCR. Focus on quality of fabrication and not exploitation of the rules.

Well, what is being done "here" is not moving the driver back to move weight back. I am only asking about the design of the cage, not the location of the driver, as it has already been determined that CMC does not want that kind of thing. As I stated in my first post above, the driver will stay put in the original fore/aft position (for CMC use) although the main hoop will be further back. For TT, PT, and AI use, the driver can be moved into the trunk, if desired.

 

Note that a significant portion of my job involves reading and interpreting various building codes; if a gray area can be interpreted in a manner that would benefit the project, then it's my job to confirm that the building department agrees so that we can proceed. So, this kind of thing is just in my wiring. I probably should have been an attorney instead of an architect...

 

Mark

[Glenn]

Still not 100% I like it. I'll go back to the other directors.

Not seeing the "2" door bars.

[TurboShortBus]

Still not 100% I like it. I'll go back to the other directors.

Not seeing the "2" door bars.

Horizontal bar just above rocker sill = 1 bar

Horizontal bar across the top edge of the numbers = 1 bar

Angled bars between them to complete the "truss" = extra support

 

Note that the upper horizontal bar will bend outward to provide more side protection (of the 3 diagrams under the car, look at the top one). IMO, this is better than the unsupported S-bends that many people put in door bars.

 

This exact photo has been reviewed by a West coast fabricator and NASA cage inspector, and he did not have any issues with it.

 

Mark

[Glenn]

I do not have issue w/ anything other than main hoop placement at this time.

 

I understand you have no plans to put any ballest in the car, but others who build based off your designes may. Since this is a loophole that will be exploited by others in the future, it needs to be prevented.

[TurboShortBus]

Well, this may or may not be a loophole. If a driver has freakishly long legs and arms, and genuinely needs to put the seat further back than the stock tracks will allow, while leaving the pedals, steering, and shifter in their OEM locations, then there will be no choice but to move the main hoop as far back as possible, which is right where it is shown in the diagram. The hoop location in the diagram matches the requirements in the CCR, so I see no violations here.

 

Slightly off topic: If you want to limit the amount of weight that is moved rearward in the car (from moving the driver back, moving ballast back, making a 90 lb trunk-mount battery box out of 3/4" steel plate and not calling it ballast, whatever), then it seems to me that it would be simple enough to write a rule that states, "The weight distribution shall be no less than 55% front and no more than 45% rear," or something to that effect (or 60/40, 57/43, etc.). If you are already weighing cars at the track in impound, then it wouldn't be much harder to measure the front/rear weight distribution at the same time. Then, it wouldn't matter where the driver or ballast were located, as long as the front/rear percentages met the requirements.

 

Mark

[Glenn]

So whats to stop someone from placing the main hoop all the way back behind everthing and calling that the "main hoop" and building other bars around the driver to protect them that would normally be done by the traditional main hoop placement? You see how quickly "Its not that big of a deal." turns into a really big deal?

 

Obviously if the directors want to set a placement limitation in the rules, we would also allow exceptions to be granted. I'm 6'3" at 250. I need my seat set as far back as possible, farther even than the OEM seat tracks allowed for. A driver like myself shouldnt need a relocated main hoop as well as relocated pedals and a slave shifter handle. If the driver is large enough to require an exception for main hoop placement, he's not gonna add ballest - well not likely.

 

In your above example you moved the hoop back, and then placed aditional bars forward of the main hoop to protect yourself.

 

As for a battery box built as you describe, it is legal, but not w/in the intent of the rules. Folks who do that are exploiting the rules and not competing on fair ground w/ those who are following the intent of the rules. Dont be surprised if that battery box issue is addressed in the off season. Its been an issue in the past.

 

Also as for limiting weight distribution.... my car has a 53% front distribution. Its mostly due to my size. I'm already coming off track post race in the 3260 range, and now you want me to have to add ballast on the nose to get my front %'s higher? You want to penalize me for being fat in a car that already has issues w/ getting to minimum weight?

Do you now see how a small proposed change has larger than anticipated affects? If would be fine if we were all driving the same platforms that were all able to be way under minimum weight prior to adding ballast, but we are not and it aint that easy.

So do you now understand why I do not like the Main hoop placement you propose?

[TurboShortBus]

So whats to stop someone from placing the main hoop all the way back behind everthing and calling that the "main hoop" and building other bars around the driver to protect them that would normally be done by the traditional main hoop placement?

 

The CCR do not call for a specific fore/aft location for the main hoop. Additional bars can be placed within the limits of the 6 point cage design in the name of safety, but not necessarily for chassis stiffening, so the scenario that you describe is perfectly legal.

 

Note that the angled bar adjacent to the helmet in the diagram is there to support the welded junction where the overhead halo meets the main hoop (HAZ). Rather than running from the overhead halo to the side bar, it could attach where the side bar meets the main hoop (running down and rearward instead of down and forward). I stole that particular support design (as shown) from a Brazilian Touring Car chassis, which seems to have slightly rearward angled bars to protect the driver in addition to the typical side bars.

 

So do you now understand why I do not like the Main hoop placement you propose?

While I understand that you are of the opinion that you do not like it, the location is not in conflict with anything in the CCR (but please advise if I have missed something, and it actually is in conflict with the CCR), which is the basis of design for CMC cages. Maybe the solution is for CMC to develop specific cage rules, if this is the case.

 

Again, I am not proposing the use of slave shifter handles, relocated seats, or extended steering columns in this thread. It has already been determined that they will not be allowed in CMC. My specific subject of this thread is the design of the roll cage.

 

My apologies, but I refuse to build what I feel could be a "dumbed-down cage" if I believe that something better can be constructed within the rules that are available.

 

Mark

[mitchntx1548534714]

...

[cmc35]

Mark - Glenn does NOT speak for the CMC directors. We are discussing this amongst ourselves. Please be patient.

 

-chris

[KiMifan]

The NHRA has a rule that requires the front plane of the main roll hoop to be within 6 inches of the back of the driver's helmet. This prevents a driver from sitting either very far forward of the hoop, or putting the hoop far behind the driver, and it exists because the primary job of the main hoop is to protect the driver in a rollover, not provide an excuse to move ballast weight rearward. The reality is that in most, if not all cars in the series, no matter how tall you are even if you have monkey arms, you cannot physically locate the seat farther back than the bulkhead that separates the passenger footwell area from the rear seat/trunk kickup, so there is really no safety reason to allow the main hoop to be in the back seat. The top of, or just behind, that bulkhead is a good location to land the main hoop onto because that is usually a strong, well-reinforced area of the floorpan, and that position will accommodate even a very tall driver.

 

The diagram in this link shows the 6 inch rule:

 

http://www.nhraonline.com/contacts/tech_faq.html

[Glenn]

Mark - Glenn does NOT speak for the CMC directors. We are discussing this amongst ourselves. Please be patient.

 

-chris

 

The only talking going on amoung the directors is the flogging I'm taking for being the only one willing to talk w/ you publically about this.

My opinions reflect the spirit and intent of the CMC rules. At one time there was just such a rule in place in the CMC rules.

[TurboShortBus]

KiMiFan...I'm well aware of the NHRA requirements, as the 6-point bar that I built in my street/strip 1994 Mustang convertible 15 years ago met those specifications. If I looked hard enough, I could still find my copy of the rulebook I used while building it. However, now that I have moved up to road racing, I am not looking at the NHRA rulebook (otherwise, I could also assume that 1 5/8" x 0.083" chrome moly tubing would be acceptable). I have seen no such clearance requirement in the NASA CCR, and I even called the main office in CA to ask about this, but the person on the other end had no useful information for me at all. Besides, what happens when a 5-foot tall person buys a caged car from a 6'-4" person? Do they have to cut up the cage and move the main hoop forward to match their seating position?

 

Taking the NHRA example, with the amount of layback in my seat, the back of it is within 8" of the front plane of the main hoop with the hoop located in the back seat area (perpendicular to the rocker sills). So, by figuring 1" for the headrest pad, moving the main hoop forward 3" would put me right at the 6" NHRA distance with the hoop still in the back seat area. I could move it as much as 5" forward and still have it behind the back seat crossbeam.

 

Glenn...I'm sorry that this has brought you unjust floggings, as that was never my intent. But, thank you for participating and being a good sport. I'll bring the beer if I manage to make it to the 2011 Nationals. On second thought, maybe we'll just mooch it from my brother.

 

ChrisM...No problem; thank you for your assistance.

 

Mark

[Trevor571548534737]

why can a tall person sit further back than a short person?

[mitchntx1548534714]

why can a tall person sit further back than a short person?

 

I've met CMC racers who are so competitive they would amputate their legs in order to get longer than stock prosthetics just to "legally" move the seating position back ... all in the name of driver comfort, of course.

[Glenn]

Attention CMC'ers.

Contact your local Direcotrs and express to them how you feel about this issue (main hoop placement). Tell them if you are OK or not OK w/ the lack of a limit placed on main hoop placement. Understand the loophole that will be exploited w/ the lack of a limitation. So far the only reason I've been given to not place a limit is "I dont want the rulebook to be 400+ pages long."