The original design may be questionable but I have redesigened this cage to comply to the following rules…
Taken from: http://www.idcracing.com/Rules/2007%20IDC%20Rules%20V1.4.pdf
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13.0 Specifications & Appendixes
13.01 Roll Cage Appendix A
Roll Cage Construction
All roll cage construction should conform to the FIA standards. It is the drivers and vehicle builder’s responsibility to
maintain their cage to any and all updated bulletins pertaining to the construction of the cage. The bellow appendix is only
to be used as a guide. Material and construction specifications and recommended designs are contained in FIA Sporting
CODE, Appendix J, Article 253, Section 8 and any supplemental updates to that standard.
Basic Design Considerations
The basic purpose of the roll bar is to protect the driver if the car turns over or is involved in a serious accident. This
purpose should not be forgotten if the car turns over, runs into an obstacle such as a guardrail or catch fence or is struck
by another car. It must be designed to withstand compression forces from the weight of the coming down on the roll-over
structure and to take fore and aft and lateral loads resulting from the car skidding along the ground on its roll-over
structure. The top of the roll bar must be a minimum of 2 inches above the top of the driver’s helmet when the driver is
sitting in normal driving position (as near the roof as possible on closed cars) and shall not be more than 6 inches behind
the driver.
The roll bar must be designed to withstand compression forces resulting from the weight of the car coming down on the
roll structure, and to take fore-and-aft loads resulting from the car skidding along the ground on the roll structure.
The roll bar must be able to withstand three simultaneously applied loads:
· 1.5 G Lateral
· 5.5 G Fore-and aft
· 7.5 G Vertical
The induced loads being carried over into the primary structure.
The two vertical members forming the sides of the hoop shall not be less than 15 inches apart inside dimension.
It is recommended that the roll bar extend the full width of the cockpit to provide maximum bearing area.
A system of head restraint to prevent whiplash and prevent the driver’s head from striking the underside of the roll bar
must be installed on all vehicles. The head restraint must have a minimum area of 36 square inches and be padded with a
non-resilient material such as Ethafoam or Ensolite or other similar material with a minimum thickness of 1". The head
restraint must be capable of withstanding a force of 200 lbs. in a rearward direction. Forward braces and portions of the
roll bar hoop subject to contact by the driver’s helmet (as seated normally and restrained by his/her restraint system) must
be padded with a protective padding of non-resilient material such as Ethafoam or Ensolite or other similar material with a
minimum thickness of ½”. No portion of the roll bar/roll cage shall have an aerodynamic effect by creating a vertical thrust.
Material
Seamless, ERW (electrical resistance welded) or DOM (drawn over mandrel) mild steel tubing (SAE 1010, 1020, 1025) or
equivalent or alloy steel tubing (SAE 4125, 4130) (T-45). Alloy steels (proof of which is the responsibility of the entrant)
must be normalized to relieve stress after welding. ERW tubing must have the weld to the inside of all bends. The roll bar
hoop and all braces must be of seamless, ERW or DOM mild steel tubing or chrome molybdenum alloy steel such as SAE
4125 or SAE 4130. It is recommended that mild steel tubing be used as chromium alloys present difficulties in welding
and must be normalized to relieve stress. Proof of the use of alloy steel will be the responsibility of the entrant. The size of
the tubing shall be determined by the weight of the car.
Minimum size requirements are:
Vehicle Race Weight Minimum Size
Under 1500 lbs. 1 1/4" O.D. x .090" wall
1500 to 2500 lbs. 1 ½” O.D. x .120" wall
Over 2500 lbs. 2 1/4" O.D. x .120" wall
Mounting Hardware
Where bolts and nuts are used, the bolts shall be at least 3/8" diameter SAE Grade 5 or equivalent aircraft quality.
Fabrication
One continuous length of tubing must be used for the hoop member with smooth continuous bends and no evidence of
crimping or wall failure. It is recommended that the radius of the roll bar hoop be such that the minimum outside width
measured at a point 4 inches below its uppermost point is 12 inches. Whenever possible the roll bar hoop should start
from the floor of the car and, in the case of tube frame construction, be attached to the chassis tubes by means of gussets
or sheet metal webs in order to distribute the loads. All welding must be of the highest possible quality with full
penetration. Arc welding, particularly heliarc, should be used wherever possible. The welds should be inspected by
magnaflux or dyes penetrate after fabrication. Alloy steel must be normalized after welding.
Bracing
Full cockpit width roll bar hoops must have two fore or two aft braces, one on each side of the hoop, of tubing with
dimensions at least equal to the minimum dimensions required for the main roll bar hoop. All roll bars must include a
transverse brace from the top of the hoop on one side to the bottom of the hoop on the other side, or alternatively, to the
bottom of a rearward brace required above. Roll bar hoops on Formula cars and cars with partial width hoops may have
either one fore/aft brace with a minimum dimension equal to the tubing required for the main hoop, or two fore/aft braces
with a minimum dimension of 1.0" x .090" mild steel or .750" x .090" alloy steel. The bracing must be attached as near as
practical to the top of the roll bar hoop, but not more than 6" below the top of the hoop, and at an angle of at least 30
degrees from vertical. If a single brace tube is used, it must be attached to the top of the main hoop. If the fore/aft bracing
must be removable, the connection between the roll bar hoop and the brace-rod must be of the double lug type fabricated
from material at least 3/16" thickness and welded through a double or gusset arrangement to avoid distortion or excessive
strains caused by welding. It is recommended that the fore/aft brace be attached to a rear chassis member through a
double lug connection. If attached to the engine, it must mount to a major component such as a head stud or combination
of head studs.
Mounting Plates
Roll bars and braces must be attached to the frame of the car whenever possible. Mounting plates must be a minimum of
12 square inches. Mounting plates, regardless of whether welded or bolted to the frame, must be at least 3/16" thick.
In case of cars with unitized or frameless construction, or cars with frames where frame-mounting of the roll bar is
impractical, mounting plates must be used to secure the roll bar structure to the floor of the car. Mounting plates shall be a
minimum of 12 square inches. It is recommended that they have a minimum area of 1.5 square inches per each 100 lbs of
Vehicle weight. The important consideration is that the load be distributed over as large an area as possible.
Mounting plates bolted to the structure shall not be less than the minimum required wall thickness of the hoop with a
backup plate of equal size and thickness on the opposite side of the panel with plates bolted together with a minimum of
three each 3/8" grade 5 bolts.
Removable Roll Bars
Removable roll bars and braces must be very carefully designed and constructed to be at least as strong as a permanent
installation. If one tube fits inside another tube to facilitate removal, the removable portion must fit tightly and must bottom
on the permanent mounting, and at least two bolts must be used to secure each such joint. The telescope section must be
at least 8" in length.
Side Intrusion Bars
The minimum side protection must consist of a horizontal tube not less than 1.50" x .095" connecting the front and rear
hoops across the driver’s door opening. Additionally, there must also be either a diagonal tube from the front hoop
bisecting the door opening below the horizontal side tube, or not less than 2 horizontal side tubes not less than 1.50" in
diameter x .095" wall thickness. Additional tubing may be added.
Installation on Cars of Space Frame and Frameless Design
It is important that roll bar structures be attached to cars in such a way as to spread the loads over a wide area. It is not
sufficient to simply attach the roll bar to a single tube or junction of tubes. The roll bar must be designed in such a way as
to be an extension of the frame itself, not simply an attachment to the frame. Considerable care must be used to add as
necessary to the frame structure itself in such a way as to properly distribute the loads. It is not true that a roll bar can only
be as strong as any single tube in the frame. On cars of frameless construction, consideration should be given to using a
vertical roll bar hoop of 360 degrees completely around the inside of the car, and attached with suitable mounting plates.
This type of roll bar then becomes a substitute for the frame.
I hope this clears things up
Thanks James
NCC Performance