Roll cages

[ERC]

The personal history.

Original cage built in 2006 to MSNZ rules/materials into a steel shelled 1950’s saloon car weighing less than 1150kg, but sadly, cage builder(s)/owner never lodged any official paperwork, though pics and details were submitted prior to painting and provisionally approved November 2006.

End 2012, request engineer’s report as MSNZ wouldn’t pass it, but they stated that as long as the engineer’s report was satisfactory, it could be homologated. No guidance was offered as to the potential for the cage to fail the freeform test requirements, so the question has to be asked “Are/were MSNZ aware of the potential test results using the older spec steel?” Equally, are/were they also aware that even if built to the required steel spec, the cage would still fail their own tests?” If not, why not?

At the risk of repeating what was published previously on another thread – this is the cage as built to the old specs and submitted to the engineer. A basic cage only was required as this is not an out and out race car, but it would be nice to race in the MGCC series for example. Equally, side intrusion bars were deemed unnecessary as access was compromised in what is still a road car and the car is quite narrow and there is insufficient space for side bars without stripping out the heavy, steel, doors, compromising the interior totally.
An extra diagonal to the hoop would also mean moving the driver's seat forward - which is also not possible given that my build and physique is rather more more Angus Fogg than Ray Williams.



After a wait of four weeks, this is what was received:

Fabricator: Finally received engineer’s response and not good news, he wants many bars added, see his e-mail below. Some of the bars (the roof diagonal especially) would be extremely hard if not impossible to 360° weld in situ to also meet the regs.

Engineer: To get the cage to meet the stricter current safety cage rules, we will need to add extra tubes as shown below:
A pillar support, a door bar, x in main hoop, a connection between x and harness bar, a roof cross, and base of rear stays to main hoop.
This is major work, it may be easier to just build a new cage to the current rules?

Engineer's demands to conform to MSNZ requirements for homologation:




After a challenge – Engineer’s response: If you look in the new manual, it has three load cases that the alternative design must meet.

These include a vertical and side load on main hoop, case (i)
a side lateral and rear load on lateral at windscreen joint (ii)
and finally a side load on the main hoop (iii)
These load case also have maximum deflections of 50mm, 50mm, and 100mm.
I think these load cases are more than the standard designs shown on pages 298-303 in the book. Especially load case ii, which will require a pillar support and roof diagonal. That is why I recommend that you build a new one as in the standard designs.

ERC:Apparently, the outer bodywork is not included in the calculations. That means that even if you installed the cage in a Sherman tank, it is only the cage performance as a stand-alone structure that counts.
Like with Dave Silcock's, removing the front cage, suddenly makes the car legal, as you do not need homologation just for a rear hoop and back stays.

Would you want to wreck these door trims to accommodate an unwanted side extrusion bar, having spent so much time and effort in making them? Not to mention that a side intrusion bar would then make the window winder inaccessible and according to T & C (sic) window winding mechanism has to remain standard.