Fitting a roll cage to a Nd era touring car can be problematic due to often conflicting needs, Schedule J of the MA handbook gives the required technical information on the cage structure which exists on one side of the discussion and on the other end is the consideration of retaining the rear seat as per original Nd era racing classes such as Group C.
Spread between these two extremes that are newer safety requirements and considerations such as HANS devices, Helmet Clearances, Seat belt angles, Emergency Exit Times, Flammable Materials in the cabin space to name a few
The latest requirements for HANS devices has put increased focus on seat belt angles which can mean non-factory seat belt anchor points are needed in some cases. . the cage structure must accommodate this.
Imposing maximum emergency exit times can require some rethinking of the height and style of side intrusion rails and also sometimes the exact location of the front legs of the longitudinal member.
Particularly tall people often struggle with seating fore-aft positions with many cage designs being totally unsuitable due to the location of the main hoop stopping the seat going back far enough. Group Nd is targeting a new cohort or racers and younger generations which are increasingly getting taller on average. Taller people are also negatively impacted by front rails intruding into the door opening.
When the main hoop is moved rearwards, there is often little or no room remaining for a standard rear seat and in some cases, not for any sort of rear seat at all.
Helmet clearance can be problematic with some designs, and sometimes a floor has to be locally lowered to give sufficient clearance to the cantrails.. some "mass produced" cages seen, have been particularly poor in this respect with scant attention paid to helmet clearance. floor shapes and sometimes cantrail designs were becoming increasingly complex in Nd period, compared with earlier historic touring car sub-groups
A lot of drivers prefer to remove the OEM fuel tank in preference for a modern Fuel Cell that is regularly mounted in the boot space and requires the fitment of a rear fire wall that needs to be sealed. This needs to be visible so officials can see its sealed and hiding it behind a rear seat makes life difficult.
Looking at all of these considerations and trying to retain a rear seat and modifying the rear seat to work with a roll cage requirements seems to to have no benefit and add a cost to the vehicle build cost to retain a flammable item within the cabin space. Other group regulations in this era allowed for the removal the rear seat.
These pictures show a recently built bolt-in cage (state racing spec) going into a Nissan BlueBird 910. Of particular note are:-
- the main hoop is mounted to the reinforced box section going across under where the rear seat squab originally fitted.
- the back stay mounts effectively preclude any sort of back seat (backrest)
- the roof side rails are tight up against the cantrails maximizing helmet clearance , but this required conventional hood lining removal
- the front legs penetrate the dash and do not interfere with door opening and thus entry/exit
- harness can be anchored by wrapping around a horizontal tube or eyelet anchors near the back, depending on seat height and harness shoulder strap angles
- the side intrusion rails offer a balance between protection and exit capabilities
