Roll Cage Technical Regulations Question

[AaronBE]

Hi, I'm building up my RX-7 for racing next year and I have a question, or a request for clarification for some of the rules in the WCMA Technical Regulations.

This is regarding the rear stays of a roll cage. In section f.ii it states that rear stays must be attached to a suitably stiff or reinforced area, but in section g.i. regarding mounting plates it states that backstays must be connected to plates on the frame or floor.

Here's the conflict; in a FD RX-7 the floor is NOT suitably reinforced (in my opinion). I want to have the backstays connected to the tops of the rear strut towers, with another transverse tube tying the two strut towers together. This also seems to be a very common configuration for this type of car. Can I build the cage as so with the justification that the backstays are connected to a suitably reinforced area?

Thanks in advance!


Below are the sections of the spec at I'm referring to:

APPENDIX 1 - ROLL CAGE SPECIFICATIONS

f. Bracing
i. In the case of the twin lateral hoop design, the front and rear hoops shall be joined by a piece
of equal dimensioned tubing on each side.
ii. Rear stays must attach to the rear hoop no lower than 20.32 cm (8") from the top of the hoop
and at an angle no steeper than 35 degrees from vertical. These rear stays must be made from
a straight piece of tubing and be attached to a suitably stiff or reinforced area.

g. Mounting Plates
i. The four lower hoop tubes and backstays must be connected to plates welded or bolted to the
frame or floor of the vehicle.

[Spec Volcanic]

Hi Aaron,
While we have made case by case exceptions to this rule, when the junction of the Backstays and the transverse bar are within 100mm of the base mounting plate, this is not preferred and your case not necessary so it should be avoided.

I would suggest you run the backstay to the front of the rear strut tower.  Attached is the Design used by one of top UK FIA cage Manufacturers, and photo of the cage where you can see the backstay mounting point if you look closely.

I would highly recommend modeling your cage after this design, with the following changes as it for a right hand drive
Run the continuous tube in the X-brace from passenger side floor to drivers main hoop top corner
Run a continuous tube for the roof bar from passenger rear to drivers front, and run a single bar not a X as there will be no co-Driver.

Gary

[AaronBE]

Perfect, this is exactly how I wanted to do it. Thanks Gary!