1.5" vs 1.75" DOM for a cage
07-13-2008, 03:04 AM
#16
Race Car
Join Date: Sep 2005
Location: TEXAS
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Chromoly is a certain weight advantage as the thinner wall and weight per foot gave me around a 30% weight reduction (calculated about a year ago.) Down side is it is a little more brittle than mild Steel. The steel seems to give a little more and not just break away like chromoly.
If you can't weld it up correctly or are able to cut the tubes to line up joints fairly close. Don't do the cage. Just too damn important - expecially if you're going through all that trouble anyway. Please have someone else do it for you.
If you can't weld it up correctly or are able to cut the tubes to line up joints fairly close. Don't do the cage. Just too damn important - expecially if you're going through all that trouble anyway. Please have someone else do it for you.
Last edited by 95ONE; 07-14-2008 at 11:55 AM.
11-26-2008, 11:00 AM
#17
Rennlist Member
From the SCCA 2008 GCR
E. Material:
1. Seamless, or DOM (Drawn Over Mandrel) mild steel tubing (SAE 1010, 1020, 1025) or equivalent, or alloy steel tubing (SAE, 4130) shall be used for all roll cage structures. Proof of use of alloy steel is the responsibility of the entrant.
2. Minimum tubing sizes (all Formula, Sports Racing, GT, and Production Category automobiles, and all automobiles registered
prior to June 1, 1994) for all required roll cage elements (All dimensions in inches):
Vehicle Weight ----------------------------------Material
Without Driver -----------Mild Steel ---------------------------Alloy Steel
Up to 1500 lbs. ----------1.375 x .095 ------------------------1.375 x .080
1500-2500 lbs. -----------1.50 x .095 -------------------------1.375 x .095
Over 2500 lbs. ------------1.50 x .120 -------------------------1.50 x .095
-----------------------------1.625 x .120
------------------------------1.75 x .095
3. Minimum tubing sizes for (all Showroom Stock, Touring and Improved Touring Category auto-mobiles registered after June 1, 1994) for all required roll cage elements (All dimensions in inches):
Up to 1500 lbs. 1.375 x .095 DOM / Seamless / Alloy
1501-2200 lbs. 1.500 x .095 DOM / Seamless / Alloy
2201-3000 lbs. 1.500 x .120 DOM / Seamless / Alloy
1.625 x .120 DOM / Seamless / Alloy
1.750 x .095 DOM / Seamless / Alloy
(American Sedans may construct to these specs regardless of weight.)
3001-4000 lbs. 1.750 x .120 DOM / Seamless / Alloy
Over 4000 lbs. 2.000 x .120 DOM / Seamless / Alloy
Note: ERW tubing is not permitted in any car registered with SCCA after 1/01/2003.
Main hoop: 4 bends max., totaling 180º ± 10º
Front hoop: 4 bends max. or
Front downtubes: 2 bends max.
Rear hoop supports: No bends.
If any of the above bend requirements cannot be met, all components
of the roll cage shall be fabricated from the tubing size(s) listed for the next heavier category of automobiles.
From the 2008 PCA Club Racing Rule Book
Minimum Roll Cage Tubing Sizes
All required tubing must have the following minimum diameters and wall thicknesses:
Car Weight without Driver
Under 2500 lbs -------------------------- Over 2500 lbs
Mild Steel 1.50" x .095" -----------------1.75" x .095” or 1.50" x .120”
Alloy Steel 1.375 x .095" ----------------1.50" x .095"
E. Material:
1. Seamless, or DOM (Drawn Over Mandrel) mild steel tubing (SAE 1010, 1020, 1025) or equivalent, or alloy steel tubing (SAE, 4130) shall be used for all roll cage structures. Proof of use of alloy steel is the responsibility of the entrant.
2. Minimum tubing sizes (all Formula, Sports Racing, GT, and Production Category automobiles, and all automobiles registered
prior to June 1, 1994) for all required roll cage elements (All dimensions in inches):
Vehicle Weight ----------------------------------Material
Without Driver -----------Mild Steel ---------------------------Alloy Steel
Up to 1500 lbs. ----------1.375 x .095 ------------------------1.375 x .080
1500-2500 lbs. -----------1.50 x .095 -------------------------1.375 x .095
Over 2500 lbs. ------------1.50 x .120 -------------------------1.50 x .095
-----------------------------1.625 x .120
------------------------------1.75 x .095
3. Minimum tubing sizes for (all Showroom Stock, Touring and Improved Touring Category auto-mobiles registered after June 1, 1994) for all required roll cage elements (All dimensions in inches):
Up to 1500 lbs. 1.375 x .095 DOM / Seamless / Alloy
1501-2200 lbs. 1.500 x .095 DOM / Seamless / Alloy
2201-3000 lbs. 1.500 x .120 DOM / Seamless / Alloy
1.625 x .120 DOM / Seamless / Alloy
1.750 x .095 DOM / Seamless / Alloy
(American Sedans may construct to these specs regardless of weight.)
3001-4000 lbs. 1.750 x .120 DOM / Seamless / Alloy
Over 4000 lbs. 2.000 x .120 DOM / Seamless / Alloy
Note: ERW tubing is not permitted in any car registered with SCCA after 1/01/2003.
Main hoop: 4 bends max., totaling 180º ± 10º
Front hoop: 4 bends max. or
Front downtubes: 2 bends max.
Rear hoop supports: No bends.
If any of the above bend requirements cannot be met, all components
of the roll cage shall be fabricated from the tubing size(s) listed for the next heavier category of automobiles.
From the 2008 PCA Club Racing Rule Book
Minimum Roll Cage Tubing Sizes
All required tubing must have the following minimum diameters and wall thicknesses:
Car Weight without Driver
Under 2500 lbs -------------------------- Over 2500 lbs
Mild Steel 1.50" x .095" -----------------1.75" x .095” or 1.50" x .120”
Alloy Steel 1.375 x .095" ----------------1.50" x .095"
11-26-2008, 12:26 PM
#18
Drifting
Glen,
Did you decide to get a cage? If so what are you going with? If you don't mind me asking what is the cost of that?
Did you decide to get a cage? If so what are you going with? If you don't mind me asking what is the cost of that?
11-26-2008, 01:35 PM
#19
Race Director
It all depends on the weight of your 911 and the rules for the organization you want to run with....for example I am building a 928 race car....In an ideal world I want it to weigh 2700lbs with cage (no driver)...so 1.75 x.095 tubing should be fine....but using 1.75 x .120 tubing allows me to weigh almost anything and pass tech even for a 3500lb car....the "loss" for using 1.75 x.120 vs .095 is about 17lbs total....but I am 100% confident my car will pass tech ANYWHERE once its done....NASA rules are slightly more strict for example...if you are over 3000lbs then you must run 1.75 x.120 tubing..
11-26-2008, 03:13 PM
#20
Racer
Join Date: Jun 2008
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4130 chromoly tubing has other issues as well, none of which by themselves is any big deal-
As mentioned, 4130 is brittle and tends to break away rather than crumple. this is bad because before it breaks it transfers practically all of its energy into the structure and anything in it (you) in a tremendous shock loading.
4130 should be TIG welded. This has a drawback in that a lot of TIG welds can visually LOOK perfect, but have insufficient penetration or worse, have been over-heated causing the joint to be even more brittle and prone to cracking. Only the welder knows how good the weld is without x-ray or destructive testing. With the popularity of "Monster Garage" "Orange County Choppers" etc. there are more "welders" who got all excited seeing something on TV, thought to themselves "Hey, I can do that" and proceeded to run out and buy a TIG machine and start making heat. The issue is that the cage you install in your car may someday have to protect your life, and you owe it to yourself and your family to NOT rely on your good buddy neighbor car buddy to weld it together. Passing tech is the BARE MINIMUM requirements, not the optimum or best for your situation. 4130 CAN also be nickel or silicon brazed, but there arent many left around using the technique.
Being so stiff, 4130 tends to transfer more energy into the car (and therefore you inside the car) than similar mild steel tubing. SCCA has limited the use of 4130 in Pro Racing because of this following several incidents in World Challenge including the Phil McClure accident a few years back. 4130 is a great material to use in a sports racer or prototype where a lot of analysis has gone into what happens when the car hits a wall, but for your average Sports GT or Sedan its simply not something I would recommend.
One theme I seem to pick up on in a cage discussion is that for some reason racers think they need the stiffest possible cage and materials and that will somehow make thier car handle better. While this is somewhat true, a properly designed and executed mild steel DOM cage will be just as "stiff" as a 4130 cage while being able to absorb energy in an impact. Now I know that the idea of the entire front of your car somehow surviving a bit more intact because you used 4130 instead of mild steel is appealing, I believe it would be less appealing if because the stiffer tubing transfered more impact energy into the car rather than absorbing it your body also took that increased energy and instead of stumbling away a bit dizzy you had to be airlifted out on a stretcher? The entire purpose of a cage IMHO is to be destroyed with the rest of the car in order for me to walk away as unscathed as possible. I can build another car, but my Mom has expressed doubts about building another me at her age.
As mentioned, 4130 is brittle and tends to break away rather than crumple. this is bad because before it breaks it transfers practically all of its energy into the structure and anything in it (you) in a tremendous shock loading.
4130 should be TIG welded. This has a drawback in that a lot of TIG welds can visually LOOK perfect, but have insufficient penetration or worse, have been over-heated causing the joint to be even more brittle and prone to cracking. Only the welder knows how good the weld is without x-ray or destructive testing. With the popularity of "Monster Garage" "Orange County Choppers" etc. there are more "welders" who got all excited seeing something on TV, thought to themselves "Hey, I can do that" and proceeded to run out and buy a TIG machine and start making heat. The issue is that the cage you install in your car may someday have to protect your life, and you owe it to yourself and your family to NOT rely on your good buddy neighbor car buddy to weld it together. Passing tech is the BARE MINIMUM requirements, not the optimum or best for your situation. 4130 CAN also be nickel or silicon brazed, but there arent many left around using the technique.
Being so stiff, 4130 tends to transfer more energy into the car (and therefore you inside the car) than similar mild steel tubing. SCCA has limited the use of 4130 in Pro Racing because of this following several incidents in World Challenge including the Phil McClure accident a few years back. 4130 is a great material to use in a sports racer or prototype where a lot of analysis has gone into what happens when the car hits a wall, but for your average Sports GT or Sedan its simply not something I would recommend.
One theme I seem to pick up on in a cage discussion is that for some reason racers think they need the stiffest possible cage and materials and that will somehow make thier car handle better. While this is somewhat true, a properly designed and executed mild steel DOM cage will be just as "stiff" as a 4130 cage while being able to absorb energy in an impact. Now I know that the idea of the entire front of your car somehow surviving a bit more intact because you used 4130 instead of mild steel is appealing, I believe it would be less appealing if because the stiffer tubing transfered more impact energy into the car rather than absorbing it your body also took that increased energy and instead of stumbling away a bit dizzy you had to be airlifted out on a stretcher? The entire purpose of a cage IMHO is to be destroyed with the rest of the car in order for me to walk away as unscathed as possible. I can build another car, but my Mom has expressed doubts about building another me at her age.
11-26-2008, 09:56 PM
#22
Rennlist Member
It all depends on the weight of your 911 and the rules for the organization you want to run with....for example I am building a 928 race car....In an ideal world I want it to weigh 2700lbs with cage (no driver)...so 1.75 x.095 tubing should be fine....but using 1.75 x .120 tubing allows me to weigh almost anything and pass tech even for a 3500lb car....the "loss" for using 1.75 x.120 vs .095 is about 17lbs total....but I am 100% confident my car will pass tech ANYWHERE once its done....NASA rules are slightly more strict for example...if you are over 3000lbs then you must run 1.75 x.120 tubing..
Can you post a link to the NASA cage rules? I can't seam to find them. I imagine that most 993s run in GTS3 (is that correct)? If that's the case (and my math is correct), that would mean that you'd have to dyno at over 272 hp to need to bring the car's weight up past 3,000 lbs. I don't think that is likely with my stock 993 engine (non-vram, no chip, etc)... I haven't dyno'd my car, but I imagine that best case scenario would be about 250 hp (which would mean the car could be as low as 2750 lbs). Please let me know if my thought process is correct here, or if there is some other compelling reason to go with 1.75" .120 mild steel over 1.5" x .120. The PCA and SCCA rule books appear to be very clear that 1.5" x .120 is sufficient for cars over 2,500 lbs (there is no designation or special requirements for cars over 3,000 lbs from what I was able to read)
Last edited by ninjabones; 11-26-2008 at 10:26 PM.
11-26-2008, 10:49 PM
#23
Race Car
I THINK that's because the site that previously had the GTS challenge rules has been replaced temporarily (that's another story). I can't find it either
my bmw (and most others) in GTS3 or 4 categories were legal with 1.5"x 0.120" or 1.75"x0.095" tubing.
my bmw (and most others) in GTS3 or 4 categories were legal with 1.5"x 0.120" or 1.75"x0.095" tubing.
11-26-2008, 11:12 PM
#25
Race Car
ah, yes. page 63 of the rulebook
11-27-2008, 03:22 PM
#26
Race Director
Okay I found this
http://www.nasaproracing.com/rules/ccr.pdf
Page 63 on the list or 77 in the PDF
Since my cage is built of 1.75 x.120 seamless my cage is over built & good until 4000lbs....but for a weight penalty of maybe 30lbs over a 1.50 x .120 cage...its worth it to me....since I could easily loose 40lbs off myself!!!!! :>)
http://www.nasaproracing.com/rules/ccr.pdf
Page 63 on the list or 77 in the PDF
Since my cage is built of 1.75 x.120 seamless my cage is over built & good until 4000lbs....but for a weight penalty of maybe 30lbs over a 1.50 x .120 cage...its worth it to me....since I could easily loose 40lbs off myself!!!!! :>)
