OUR SHED, OUR CARS, OUR STORIES
DESPITE HAVING driven plenty of race cars over the years, having built my own many moons ago and helped spanner up countless others, when it came time to organise a roll-cage for my hillclimb project, I didnít really know where to start. So I went to the go-to guys for stuff like this; Brown Davis in Melbourne.
And I went straight to the top Ė to the bloke whose name is above the door Ė David Brown. Brown Davis, you will recall, was responsible for the fuel tank in our giveaway Torana Ė amazingly, they still sell about two of these tanks a week. So when it comes to metal fabrication that absolutely canít afford to fail (and Iíll put my roll-cage into that category) itís a brand we trust here at UC. None of which altered the fact that I had no idea what I needed.
Davidís first question was a simple one: What specification was I building the car to and at what level (CAMS uses club, state or national levels while ANDRA uses elapsed times) did I plan to run it? The regulations have a minimum standard for each category of car (Iím building mine to Improved Production specs) which is overlaid by a further minimum depending on the level of the event (the club, state, national thing again).
ďThe last thing you want to do is fit a roll-cage that you think is going to be enough, and then get knocked back at scrutineering because the cage doesnít comply,Ē David explained.
Turns out, for what I want, I could probably get away with a four-point cage, and while David admits a well-designed, well-built four-pointer can do the job, he reckons a six-point cage is a better bet for most people. Thatíd be me, then.
Now, either is designed to keep the roof off your head in a roll-over, but the six-pointer should definitely keep the windscreen and the roof header rail out of your face as well. I like that idea.
ďWith a six-point cage, youíve got multiples of extra strength,Ē says David, ďand done right, a six-point cage can add a lot of strength to the carís existing structure.
Thatís what a lot of people donít understand: Youíre not just adding safety, youíre adding stiffness.Ē
So, having made the decision to go with a six-point set-up, the next decision is easier. Says David: ďFor not a lot more money, you can make additions to the basic six-point layout that hugely improve the safety. You can add a footwell bar (to prevent intrusion into the pedal area
in a shunt) a harness bar and a roof diagonal which drastically increases the cageís ability to deal with loads at the front of the roof. Every time you make a new triangle, youíve made the cage stronger. Think triangles.
ďAnd once you have a sixpoint roll-cage, to not add a side intrusion bar is just silly.
Like the other additional bars, itís very easy and very cheap to do, yet itíll make the car so much safer. But youíve got to have a six-point cage to start with for all this to apply, so thatís why I recommend them.Ē
Of course, even then, side intrusion bars aint side intrusion bars. ďA ladderstyle side intrusion bar is far superior. With the X-type bar, you end up with all the forces of a side impact going through a single point (the centre of the X). And thatís a point youíll already have compromised by welding it. The ladder-style side intrusion bar actually gives 48 per cent more impact resistance than the X-type.
And if you tie the intrusion bar into the carís sill, it increases even further.Ē
So what else do you need to think about? Well, David reckons cold-drawn seamless steel tube Ė not black pipe Ė is the right stuff for building cages because itís consistent in metallurgy and wall thickness. No nasty surprises, in other words.
But donít forget that not all roll-cages are CAMS (or ANDRA) approved, and to be approved the cage really shouldnít protrude past the limits of the front and rear axle line. ďThatís so the cage doesnít compromise the carís existing, engineered crumple zones,Ē David explains. Also, all joints need to be fully welded right around, not halfway or even three-quarters round.
Speaking of welding, that brings me to my final question: Weld-in or bolt-in? David reckons the weld-in cage offers the most additional stiffness, but a bolt-in cage also has advantages. It gives you the ability to swap the cage to a new shell (should that be necessary) and provided itís still in good nick, a bolt-in cage can be removed and sold on to finance the next project.
Every roll-cage is a bit of a compromise, to be honest.
I mean, youíve got to leave space for a big lump of a driver (Mother says I have big bones) and that same driver has to be able to get in and out and see out of the car when he or she is inside. But I reckon climbing over a side-intrusion bar is a small price to pay for knowing that should it all go pear-shaped, Iíve a much better chance to crawl back out over that same intrusion bar in one piece.
So now that lotís decided, itís time to bolt her in.