Mustang roll cage questions...

Questions and answers about CMC and NASA rules

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85306Fox
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Mustang roll cage questions...

Postby 85306Fox » Sun Jan 18, 2015 7:55 pm

I am having the roll cage installed in my future CMC Mustang and have a question regarding the rear shock towers and the tying of them into the cage.

Would such down bars as those in the picture below be considered legal for CMC?

Image

I read over the 2015 rules as well as the CCR and could not find any reference to the cage being welded to the body of the car in locations other than the specific mounting points. For whatever reason, I seem to recall there being a CMC specific rule stating the cage could not be welding to the body. For example, the main hoop can not have plates extending so that it is welded to the b-pillar and the front bars can not be welded to the a-pillar... Maybe I am just overlooking the rule.

My question is then can the cage be welded to the body of the car in locations other than the mounting points?

If so, are there any restrictions?

Thanks in advance...

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BADVENM
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Postby BADVENM » Sun Jan 18, 2015 8:14 pm

Post removed since original was original one was speculation.
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Postby MHISSTC » Mon Jan 19, 2015 2:44 pm

Is the photo you're showing something that has already been done to your car, or is it merely an example of another persons handy work that you are using as an example?

Re-read ALL of CCR 15.6, and take another look at the diagrams also.

Overall, I believe there is a better way of accomplishing what was intended in the example pictured without using those little vertical stubby attachment points. Those additional attachment points count towards your cage attachment points count, which cannot exceed 8, and are not specifically mentioned in the CCR. The first two mounting points would be the main hoop, the second two would be the front ends of the forward hoops. Points 5 and 6 should be the ends of the rear braces. Points 7 and 8 are intended to be the ends of short bars that extend forward from the front hoops to the wheel front wheel wells/floor to prevent the front portion of the floor from pushing into your feet breaking any bones in your lower legs and feet in the event of a hard front end collision.

I also don't see a diagonal in the main hoop extending from over the drivers head to the lower passenger side.

Now back to the subject of the rear braces. Start with rear braces that go straight from the top of the main hoop back to the rear brace mounting points on the floor of the rear hatch area. If you terminate those braces in a single point on plates that are flat on the floor, and a portion of those plates also extends up the side of the shock mount and those plates meet, but don't exceed the maximum mounting plate area specified, you'll be fine. Then you may optionally add one or two diagonals between those braces. You could also add a single bar between the lower ends of those rear braces to fully close the triangles formed by the bars. You could even go the extra mile and triangulate the lower ends of the rear braces to the lower ends of the main hoop. That's probably beyond going the extra mile and venturing into overkill zone, but it's still legal.

Can you attach the cage to places like the A-pillar or B-pillar? No where in the CCR does it say that you can. Therefore you cannot.

Some individual series rules go beyond the CCR and specifically mention attaching the cage to the A-pillar and B-Pillar. CMC does not.

Now review CMC rules section 4.12. That's the only section in the CMC rules that adds anything to the CCR with regard to cages and specifically address door bars. No where else in the CMC rules does it mention any additional attachment points around the vehicle. Therefore you cannot.

You'll also want to take a closer look at CMC rules section 7.6 that specifically references cage attachment points 7 and 8. You don't want those points coming to close to the attachment points of a strut tower brace that attaches to the firewall, if you use one.

Clear as mud?
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Postby 85306Fox » Mon Jan 19, 2015 8:02 pm

Scott... Thank you very much for the reply.

The car in the photo is not my car. I am in the process of working with the fabricator regarding deciding how to do the rear bars. He stated that on Mustangs he will normally do the rear bars much like those in the photo.

I could have sworn I read sometime ago there being a written rule about the cage being welded to the body. Oh well, I guess old age is kicking in...

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Postby BADVENM » Mon Jan 19, 2015 8:08 pm

I did look at mine last night. My horizontal rear bar is ahead of the shock towers, tying in the 2 diagonal bars.

Scott and I talked about the car you provided the picture for. I knew the NASA CCR had something about cage design in it but forgot about the number of mounting points you're allowed.
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Postby MHISSTC » Tue Jan 20, 2015 12:04 am

Is your fabrication shop familiar with road race cages and the NASA CCR? If not, you may want to find another shop or make sure you provide them with a copy of the CCR and CMC rules to familiarize themselves with it.

Maybe some pictures will help.

Pardon my Paint program skills and focus on the basics. I drew it over your picture, so ignore the installed cage. All bars should also be placed as close to the shell of the car as possible while still being able to make complete welds around the tubing.

Picture #1. Your entire cage is based on your main hoop (shown in black). This is a main hoop with the diagonal bar and the horizontal bars commonly used as a harness bar. Specifics are listed in the CCR.

Image

Picture #2. Add to that the forward bars that follow the roof forward to the A-pillar, down the A-pillar and behind the dash down to the floor where it mounts to a plate or a plinth box. Also included are the header bar at the top of the windshield and the dash bar that is located along the firewall behind the dash. (shown in grey)

Image

Picture #3. Then add the rear support bars and bars that attach between the front bars and the firewall/wheel well. (shown in yellow) I also outlined basic attachment plates in a thin black line.

Image

Picture #4a. Then you can add optional bars. I'm specifically showing the arrangement of two diagonal bars and one horizontal triangulation bar since your original photo showed something similar. Also shown is a bar that goes from behind the drivers head at the main hoop forward and diagonally to the top of the right front bar where it meets the windshield bar. This provides some additional roof protection and triangulation to the cage.

Image


Picture #4b. Another option with the bar across the roof is to mount it longitudinally between the main hoop and the bar at the top of the windshield. This is less desirable than the diagonal bar across the roof because it does not connect at the intersections of other bars to transfer loads, but it does still provide additional roof support while sometimes affording more head room and is a popular choice for t-top cars.

Image

I hope all that helps.

In order to concentrate on a basic 8-point cage design, I purposefully left out things like rocker bars, door bars, and a multitude of other gussets and optional bars folks commonly install There are more variations of that other stuff than I care to try and draw. Look around on this forum, across the Internet, and in person at NASA events for more cage design ideas. If you find something interesting, post a picture and ask more questions.
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Postby 85306Fox » Tue Jan 20, 2015 6:14 am

Scott... Again, thank you VERY much for the time and effort you put into your post and art work. I really appreciate it!!

The fella fabricating the cage has done several NASA cages and is familiar with the CCR. The majority of the cages he has done are mainly for BMW's and Porsches. He has also done several SCCA cars but just recently began doing cages for Mustangs.

He is one of the few folks that offer "road race kit cages" and will be using my car to provide all of the measurements, etc... for the Mustang cage kit he plans to offer in the future.

My car will be the first CMC car he has done which is why we want to make sure everything is legal by the CMC rules.

I am going to forward a link to this thread to him as I plan to meet with him later in the week so we can finalize the design. If there are any questions or concerns I will be sure to post them here...

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Postby D. Francis » Tue Jan 20, 2015 8:27 am

Don't overlook this either:

CMC Rules wrote:15.6.14 Mounting Plates
Each mounting plate shall be no greater than one hundred (100) square inches, and no less than nine (9)square inches. Each mounting plate must be no greater than twelve (12) inches or less than two (2) inches on any side. Welded mounting plates shall be at least 0.080-inch thick. Plates may extend onto vertical sections of the structure. Any mounting plate may be multi-angled, but shall not exceed one hundred (100) square inches total including vertical sections.


Good luck on the build.
David Francis
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BADVENM
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Postby BADVENM » Tue Jan 20, 2015 8:28 am

Don't forget the door bars. Also, what kind of seat are you getting? You may want to add a mount (Scott can "paint" it in) so when the seat expires the mount will allow the seat to be legal. I'm trying to attach some pics I just took of mine to show you but haven't got it to work yet.
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