Just brought a roll bar and it needs some reinforcing base plates, any ideas what size they should be and what thickness steel would be advisable.
My main thought is should they be bigger than the plate on the interior side but how much bigger due to space issues on the external side.
Alex
The spreader plates underneath the floor on my cage are 3mm thick steel and as large as I could make them in the space available. BDC regs said they had to have an area of 5 squre inches, but that seemed terribly small to me. Mine sailed through scrutineering. For the bolts make sure they are grade 8.8 or 12.9 (the grade should be stamped on the head of the bolt) avoid cheap bolts from B&Q or wherever.
I had a quick google for MSA specs as a better guide line for you, but nothing popped up immediately.
Bit late to the party, but MSA cages have to fit to welded mounts
Depends where you look in the Blue Book, and under what regs you are looking at. In the Road-going sprinty/hill-climby section, there is no requirements for rollbars per se, but there is a section (bit foggy, as GerryN went off with my old copy years ago) that goes through a series of recommendations, as a to construction/fitment. Local competition regs may make additional requirements, but sometimes these are pretty loose. I’ve seen camel hump style bars pass scrutineering before, no problem (though the same scruitneers get a bit sniffy about the factory battery mounts). Bolt-in bars aren’t actually prohibited. There aren’t many MSA-approved cages for the MX5 (3?), and none are suitable for road going cars.
Funnily enough, in the JAF equivalent book, there is a section there specifically prohibiting the use of harness bars in Roadsters.
The Captains point was look to MSA regs for more info, there won’t be any for bolt in cages.
However, typically the spreader plate underneath a bolt in cage will be the same footprint as the foot inside the car.
There are lots of differing roll deviced in MX-5’s and lots of different opinions as to how good. As with all these things you have to define what “test” it is ment to comply with before iy can be said to be effective or not.
We have this one
which is essentially one of these, modified to fit under a hood. The idea is that it can be driven to competition if necessary. The vertical’s could be added back in, just he didn’t want to loose the center console.
http://www.msauk.org/uploadedfiles/msa_forms/bluebooks/10/160-195%20Competitor%20Safety.pdf
If a rollbar is required, only the backing plate needs to be welded in, not the whole rollbar. Of course, if a rollbar isn’t required, the backing plate need not be welded. And the guidance on welding standards is rather wooly.
Note, the MSA isn’t the be all and end all if you are looking for guidance for a non-licenced motorsport application. SCCA SOLO rules for instance permit bolt in bars. In Australia, CAM approves a rollbar (Brown-Davis) for road-going motorsport that some here would regard as little more than a style bar (fully bolt in, rear stays on large backing plate, resting on the rear shelf).
Do you have the main hoop dimensions for that “inside soft top” cage Nick?
I’m looking at designing one that replaces the rearmost bar in the soft top (just leave it out and let the soft top rest against the main cage hoop), where the main hoop sits in the “Hard Dog Hard Core Hardtop” position (centred on where the 3rd bar of the soft top is, rather than the 2nd bar). Dimensions (if available) would be grand.
The other thought is to have 3 optional bars between the main hoop and the windscreen surround. Two top bars that mount to the main hoop and the windscreen frame’s soft-top hardpoints, and a 3rd diagonal that joins the corners fo these. Not race legal I’m sure, but plenty good enough to keep the windscreen frame from moving in a light roll and you can store the things in the boot en-route to hooliganism.
An internal-external cage is another option. Main rear hoop for standard work, plus pop some holes through the front wings, and pickup on the bonnet mount points or door hinge mountings for the front structure for hooligan work. Could probably get that one MSA approved too, though it’d be trickier to fit/de-fit.
Hi Mark,
Please don’t take this the wrong way, safety is important to us all, however not a small amount of money, time and effort was expended to get to that first off point and revisions are still required which only a lack of time and a change in circumstances of the car owner are preventing. A fully functional hard top was also cut up to see clearances, so to be fair I am not in a position to give away that info. Obviously there is nothing to stop you measuring a car.
As with all of these things, any product in fact, I come back to the point, to define if it “works” you have to define the test that it has to pass. While I am not aware of any physical practical test that the Blue Book insists on, and by the nature of competition cars, having to write one off just to prove the cage is OK is never going to be a viable option. However experience gained over years is used to define the regulations.
For MSA approval the regulations state that either the main roll bar, the one behind the drivers head and the one around the windscreen must be one piece with no joins or the lateral ones, the ones that would follow the door aperture must comply with this. While cages can pass through dash boards, they have to fit to welded mounts, so bolting to suspension or bonnet mountings is not sufficient and also I very much doubt would comply with the requirement for the front roll hoop the hold the windscreen up, the more horizontal the front legs, the less vertical strength they have. Door bars would also be difficult.
While not pretty, this video shows why competition roll cage design is so strict, and types of joint, quality of material and mounting and fixings required.
Not at all Nick, I hadn’t realised that was a commercial cage. I’m a MechE and the MSA regs aren’t bad at all as design guidelines - follow them (and the spirit of them) and you’ll have a perfectly adequate cage for the purposes of going over onto it. The strength is all in the main hoop/diagonals/stays. Get 'em right and provided you don’t fold the shell in half (not impossible) you’ll be mostly safe. Hitting your head on the tarmac with a helmet on as your head flails sideways isn’t great but isn’t killer, though cracking it against a rollbar tube in say a mild frontal shunt can be. (and there are a lot of MX5s with rollbars too short/seats too high for the occupants who don’t always wear helmets!)
Three bars above the roof would stop the screen folding provided that the shell’s structural integrity wasn’t compromised in the shunt, and reduces the risk of the main hoop digging into soft ground. Not enough where the MSA regs call for a proper roll cage, but very preferable to not having them and possible to stow-away for road use. (the bars can sit above where the roof normally goes, so you go open-only on the trackdays and closed without the bars. The other one I was considering is where you pop the mounts under the front wings (pick up the bonnet/door hinge/suspension mounts - you weld to them, but I’m citing them as the designed in hard points) and have the mounting plate (with captive nuts) just underneath the surface of the front wings. Then you’ve got a demountalbe (single piece) front hoop (without or without bar below the screen) with your longitudinals and diagonal/x-bars that mounts to the main hoop. Again, keep the main hoop for everyday work and have the demountable front end of hooliganism. You’d not be able to comp with the roof up though. Again, once the shell integrity is compromised the windscreen would come down, but until then you’re fine. Only way to sort this would be completing the triangles in the door apertures, rather than assuming that the ‘U’ formed by the shell stays together.
Will snap a photo and do some sketching - I’d be curious what you’d think to it.
50x2 mm alloy steels or 45x2.5 mm cds mild? Ever worked with 1.7734.5/15CDV6 rather than T45 or 4130 - strong yet moves forever before failure.