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Old 02-07-2012, 06:17 PM   #16
MichaelP
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Default Re: Roll Cage 25.1 Specs

I'll bet that it's not necessarily that the round tube is stronger than the 2x3, it's that they figured all cars getting certified at that level would be weight conscious enough that they would be 4130 round tube construction, and didn't want to run the stress calculations for a mild steel 2x3 version!
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Old 02-07-2012, 08:38 PM   #17
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Default Re: Roll Cage 25.1 Specs

I totaly agree!

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Old 02-07-2012, 08:40 PM   #18
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Default Re: Roll Cage 25.1 Specs

This all stated by asking were to put the seat belt mounts..............next time I'll keep my moth shut!

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Old 02-07-2012, 10:25 PM   #19
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Default Re: Roll Cage 25.1 Specs

.

Trust me, a bunch of us don't think it makes sense.
Now I would never use 2x3, but from what I keep reading, there is nothing wrong with mild steel.
Hell, the roundy round guys use it??

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Old 03-12-2012, 10:49 AM   #20
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Default Re: Roll Cage 25.1 Specs

I have another couple questions, do any of you guys set in front of the main hoop? If so how far in front of you is the funny car hoop? I have a couple questions about the SFI design regaurding the shoulder bar as well, I want to put my shoulder bar across the main hoop were it has a bend not a foot off the floor, can I run the shoulder bar up there? I don't need the suspention to mount to the main hoop like they call for.

Anyways I'll try and post some pictures because they will tell you more then this dam keyboard.

Thanks again!
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Old 03-12-2012, 11:28 AM   #21
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Default Re: Roll Cage 25.1 Specs

"1. Round tube weighs less than square tube."
True - for a given outside dimension there is less material in a round tube.
"2. Round tube is available in stronger steel. There is no rectangular frame made from 1020 cold rolled steel, which is 37% stronger than 1010 square tubing. "
According to my references, A500 (rectangular material) has a yield strength of 58 Kpsi, 1020 cold roll @ 78 Kpsi (as far as I can tell, this is not used in tubing larger than 2"), 4" DOM tubing (the most likely that FF is using) is 70 Kpsi in sizes above 2.75" OD. So the advantage in MATERIAL STRENGTH ALONE is from 21% to 36%. Of course, this does not take into account the shape or size of the tube, only the material. A 4" x 3" rectangular tube put in vertical bending mode will support about 11% less before failure than the higher yield strength round tube. Have you ever heard of a chassis failing in this mode? Me neither...
If a chassis has a structural failure in a main rail, you've got much bigger problems than I can describe here.
BUT, strength is not a big factor in overall chassis design, STIFFNESS IS. For an article on stress vs stiffness from Machine Design Magazine, click here.
"3. In Torsion, (exactly the kind of stress that cross members are subject to) round tubing is more than four times stronger than square tubing."
First of all, see the previous answer about stiffness vs strength. But there appears to be an error in their math anyway. My results for stress/unit torque are:
4" x .125"W Round tubing > Torsional stress (psi) = .35 x Torque
4" x 3" x .125"W Rectangular tubing > Torsional stress (psi) = .39 x Torque
So the "four times as much" difference is really a little over 11%.
Please check my math! Here are the formulae (taken out of a mechanical engineering reference book):
Where the variables are calculated as follows: For a round tube:For a rectangular tube:
"4. Under vertical bending loads, square tubing made from the same steel as round is stronger, but go back and read #2, hence, there is no significant difference between 4" cold rolled 1020 round tube and 4" square 1010 tubing with respect to vertical bending loads (same as thickness)."
Again, see my comments above about strength vs stiffness.

"5. The end result of using round tubing is the lightest ladder frame possible, with superior torsional load rigidity and vertical load resistance equal to any square tube design."
Again, in a complex structure, it is the total design that determines rigidity, not individual pieces. Their claim over "any square tube design" is taking hyperbole a little too far.
"6. Perhaps the most interesting fact is that square tubing is easier for the kit car manufacturer to work with and is half the price."
In order to be a better overall design, our chassis is much more difficult to build than FF's. The difference in material cost is only about $40. Our chassis uses rectangular tubing because it works better in this application. Consider the chassis of the new C-5 Corvette. They start out with a round tube - it's easier to bend. Then they cap the ends and use hydraulic pressure to form the tube into a rectangular shape in steel dies. They do this extra step not for economy, but because it makes a better chassis. ERA gets the same effect by using rectangular tubing from the beginning, although we have the added effort of cutting and welding to get the ideal basic chassis design.
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Old 03-12-2012, 12:19 PM   #22
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Default Re: Roll Cage 25.1 Specs

Quote:
Originally Posted by Biginchmopar View Post
I have another couple questions, do any of you guys set in front of the main hoop? If so how far in front of you is the funny car hoop? I have a couple questions about the SFI design regaurding the shoulder bar as well, I want to put my shoulder bar across the main hoop were it has a bend not a foot off the floor, can I run the shoulder bar up there? I don't need the suspention to mount to the main hoop like they call for.

Anyways I'll try and post some pictures because they will tell you more then this dam keyboard.

Thanks again!
It was discussed in this thread starting at post #937:
http://www.yellowbullet.com/forum/sh...d.php?t=167144

The above info on the square vs rectangular tubing is interesting. Basically rectangular tubing can be both stiffer & stronger in a given direction, but for all directions (both bending and torsion) you will never beat the efficiency of a round tube, which places its mass uniformly as far away from the centroid as possible.
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Old 03-12-2012, 01:21 PM   #23
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Default Re: Roll Cage 25.1 Specs

Thanks MichaelP!

I have been trying to get ahold of NHRA Division 7 Tech but they haven't returned any of my calls. I would love to have some pictures of a 25.4 -25.1E cars with the helmet in front of the main hoop bar #10 and were the funny car cage is in relation to the main hoop.

Thanks again guys!
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Old 03-12-2012, 03:54 PM   #24
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Default Re: Roll Cage 25.1 Specs

I can show you photos of how NOT to do it! Mine was just barely protruding at the forehead area, but I have since cut out that whole section and am redoing it such that the FC bars are in front of the entire helmet, including the chin area.



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1973 Pontiac T/A 455
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Old 03-12-2012, 06:11 PM   #25
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Default Re: Roll Cage 25.1 Specs

Any photos are good, just trying to see a design that will pass. I also need to be able to get in and out of the car.
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Old 03-12-2012, 07:07 PM   #26
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Default Re: Roll Cage 25.1 Specs

On my new cage section (still in progress), both the FC cage tubes (40A & 41B) will sweep forward then sweep back as they go downward, to protect the helmet but allow me to slide under them a bit when getting into the truck.
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1974 Vega bracket car, 350" SBC
1973 Pontiac T/A 455
1992 GMC Typhoon
1973 Chevy Blazer with Pontiac 400
1995 F350 Crew Cab Dually - intake, exhaust, chip, injectors
2000 VW Jetta TDI - Kerma tuning, Der Chimera clutch
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Old 03-12-2012, 07:14 PM   #27
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Default Re: Roll Cage 25.1 Specs

25.5 can be mild, but like stated it is a no faster than 7.50 spec..
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Old 03-12-2012, 08:26 PM   #28
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Default Re: Roll Cage 25.1 Specs

The only thing keeping me from getting a 25.1E is my inner frame rails, the rest is all moly, I'm trying to see if we can run moly inner frames through the cage area only. I'm hoping to get some answers soon. The car has a four link and struts but it has 2x3 .083 MS inner frame rails. If I can't get a 25.1E I guess we will just have to make it a 25.4. I know I'm being stuburn but I don't want to mess with the suspention again.

Thanks for the help!

I keep getting different answers on were the funny car cage goes so once again the helmet will be in front of the main hoop #10

Do you guys know if you have to follow the design in the SFI book to a tee? I'm hopeing you don't because ever car is different.
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Old 03-12-2012, 10:17 PM   #29
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Default Re: Roll Cage 25.1 Specs

with the tech guy down here you have to follow it to a tee to pass. Make sure use the same spec all the way throw your build.
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Old 03-12-2012, 11:01 PM   #30
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Default Re: Roll Cage 25.1 Specs

just got my car certified 25.4 7.50 @ Richmond Dragway . all chrome moly round tube . good for 3 years. i need to make a couple of changes and it will cert. 6.00
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