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   However, I feel that a lack of complete understanding on behalf of some of the technical officials at that event led to TGP being pressed to issue instructions to some teams to modify or re-manufacture their roll hoop structures. The respective teams subsequently modified the cars in question. However, in some cases but in others may have created more problems than it solved.

   Two cars in particular have been modified in a fashion that, although fixing the original problem do not now comply with the FIA regulations for Roll Over Structures on other issues.

   Below are some extracts from the relevant Articles of Appendix 'K' relating to rollbars/rollcages and guidelines again from Appendix as to the standard of materials, workmanship and structural requirements.

   Article 10.11 Appendix K - Rollbars/Rollcages
i) Requirements:

Periods F, G, H, & I, (represents potential TGP cars): Roll bars/rollcages providing adequate protection are obligatory, except for series Production Touring cars and Grand Touring cars for which they are strongly recommended. These rollbars/rollcages may meet the period specifications (except with regard to constructions made from light alloy, see below), or if not must be built according to the specifications set out in this article.
Aluminium cages are banned in any period unless they are an original irreplaceable, integral part of the cars structure (eg. Porsche Carrera 6, 908, 917)
ii) Specifications:
For Period F Formula 1 cars, if the safety rollbar is an integral part of the vehicles structure, it may be used in place of the one stipulated in this Article 10.11
For other single -seater and two seater racing cars and open GT, GTS and GTP cars: a rollbar confirming to Art.277 of Appendix J 1993 (see Appendix Vll to this regulation).

   Article 277 of 1993 Appendix J - Rollbars
The dimensions of the rollbars must be as follows:
The minimum height must be at least 36 inches (92cm) measured along the straight line following the driver's spine, from the seat's metal shell to the top of the rollbar. The top of the rollbar must be at least 5cm above the driver's helmet when the driver is sitting in the normal driving position. The width must be at least 38cm measured inside the rollbar between the two vertical pillars of the sides. Measured at 60cm above the seat's metal shell on the perpendicular to the straight line following the driver's spine.

Strength

In order to obtain a sufficient strength for the rollbar, two possibilities are left to the manufacturers:
a) The rollbar, of entirely free structural conception, must be capable to withstand the stress minima indicated in Article 275.15.2.3. with 'W' being 740Kg.
b) The tubes and brace(s) must have a diameter of at least 1.375 inches (3.5cm) and at least 0.090 inches (2.0mm) wall thickness. The material should be molybdenum chromium SAE 4130 or SAE 4125 (or equivalent in DIN, NF, etc.)
There must be at least one brace from the top of the bar rearwards at an angle not exceeding 60 deg. to the horizontal. The diameter and material of the brace must be the same as those of the rollbar itself.
In the case of two braces, the diameter of each of them may be reduced to 20/26mm.

   Article 275.15. Safety Structures
15.2 Rollover structures:
15.2.1 the basic purpose of safety structures is to protect the driver. This purpose is the primary design consideration.
15.2.2. All cars must have two roll structures.
The principal structure must be positioned behind the driver. The second structure must be in front of the steering wheel but no more than 250mm forward of the top of the steering wheel rim in any position.
The two structures will be of sufficient height to ensure that the driver's helmetand hid steering wheel are at least 50mm below a line drawn between their highest points at all times.
15.2.3. The principal structure must pass a static load test details of which may be found in Article 15.2.4.
The second structure must be capable of withstanding three loads applied simultaneously to the top of the structure which are 12kN laterally, 45kN longitudinally and 60kN vertically.
15.2.4 The principal roll structure shall be subjected to a static load test. A load equivalent to 12kN laterally, 45kN longitudinally and 60kN vertically, must be applied to the top of the structure through a rigid flat plate which is 200mm in diameter and perpendicular to the loading axis.
During the test the roll structure must be attached to the survival cell which is supported on its underside on a flat plate, fixed through its engine mounting points and wedged laterally, but not in a way as to increase the resistance of the structure being tested.
Under the load, deformation must be less than 50mm, measured along the loading axis and any structural failure limited to 100mm below the top of the roll structure, measured vertically.

Note

It is not reasonable to suggest that TGP cars are subjected to such tests, subsequently for each competitor who has carried out modifications for whatever reason it must be possible submit a certificate on a form approved by the ASN and signed by a qualified technician to the events scrutineers. It must be accompanied by a drawing or photo of the rollbar in question declaring that this rollbar can resist the forces mentioned in the relevant regulations.
Rollbars must not be modified.

Main structure

One continuous length of tubing must be used for the main structure with smooth continuous bends and no evidence of crimping or wall failure.
Minimum bend radius = 3 x Tube o/dia.

Welding instructions

All welding should be of the highest quality possible with full penetration (preferably arc welding and in particular heliarc.) Although external appearances of a weld does not guarantee its quality, poor looking welds are never a sign of good workmanship.

Materials

When using heat-treated steels the special instructions of the manufacturer must be followed (special electrodes, welding under protecting gas.)
It must be pointed out above all else that the manufacturer of heat-treated steel, and high carbon steels may cause certain problems and that bad construction may result in a decrease in strength (crinkling) and an absence of flexibility.

Conclusion

I suggest that over the winter period everyone takes a look at the regulations and makes sure that their cars comply. It is strongly recommended that if it is thought to be necessary to replace the original roll hoop structure in order to comply with the relevant regulations that the work is carried out, if possible by a repair facility recommended by the vehicle manufacturer or an experienced fabrication company familiar with aero/automotive monocoque fabrication.