I recently picked up my 818R kit and am looking at modifying the chassis to allow the upper side bars to be removed.

The general consensus seems to be that these bars would be a head crusher if used without a helmet and I agree. I would like to make them removable so I can drive the car on the street on occasion without a helmet.

The other concern is to keeping the chassis able to pass race scrutineering.

FIA: rules seem to allow for removable elements of the roll cage if using the correct joint type (FIA Appendix J, Art.253, 8.3.2.4)
NASA: Rally would seem to not allow this mod, but I am not sure as they do reference the FIA Appendix J document. Time Trial and HDPE seem to be fine
SCCA: Seems to be fine but the rules are not clear about exact joint requirements. The FIA joints might be acceptable, but I am not sure.

Using the FIA Appendix J as a reference, I came up with the following:

There are three cuts to make. One close to the main hoop that leaves a ~3" stub needed for the joint. One close to the dash leaving about 2" sticking out to allow the removable member to be bolted in. And finally, the vertical support member cut about 3" above the small forward brace.
Removable_door_bar_cuts.jpg

A quick mockup in CAD to show the joints. All joints are made with 1.75", 0.12"wall DOM tube. SCCA rules may require use of a double bolt per joint so the FIA 253-41 style joint would need to be used instead. The overall length of the coupling sections remains the same at 5.75"
Removable_bar_joint_detail.jpg

An overview of the parts of the connection system. The vertical tube connector must be welded to the removable section as there is not enough space for a fully bolted joint.
Removable_bar_exploded_view.jpg

Some areas of concern:
1. The stub on the main hoop sticks out about 3" into the driver/passenger area. I think that this is out of the way and highly unlikely to intersect with a head in an accident. This may also depend on the seating system used.
2. The forward section of tube under the dash may need some bracing to keep it from moving when the bar is not in place.


This seems to meet the needs of a removable side bar system for the 818R but I am not an expert and thought I should get some feedback before cutting my frame