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      07-24-2019, 06:22 AM   #1
Vanne
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racing cage for Z4?

Hey guys, just putting this out there to make sure I haven't missed something blatant?

looking at this one.

https://www.customcages.co.uk/roll-cages/bmw-z4-coupe



T45 is a must as is FIA approval.

any info/help will be appreciated.

Recommend any other cages? aside from totally custom, this looks like areally good option. ESP with CAMM's being such shitheads back home in oz.

Pic of said cage installed

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Last edited by Vanne; 07-24-2019 at 06:31 AM..
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      07-24-2019, 06:51 PM   #2
Michael9218
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Is your intention to someday go racing with this car? If so, know the cage rules. You can over build the cage and be disqualified from the class you intended to run in.
If not, why so much cage?
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      07-24-2019, 11:33 PM   #3
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GDay Michael,

Was hoping you'd drop in and have a chat.
The intent at the moment is to create a really nice and light track car, but I am not ruling out racing at home in Oz later-on, or possibly here in Dubai. Camms (racing body back home in oz)rules are pretty tough, and any cage must be FIA approved.

It is of course possible to change the cage lateron, which would be cheaper for me in the mean time also, so I am ok to go down that route.

The biggest issue I have with the cage design above is that it hooks into the rear strut towers, which I don't like. Its easy for the cage builder, but could be dangerous.

The other issue I have with the above design is that if I have the strut bars along the sides of the seats, it WILL prevent me from being able to road register the car. (I am actually not completely sure how the body kit and all the other bits and pieces are going to go down at the RTA come registration time, probably not well I would imagine anyways

So I was thinking about designing my own cage, borrowing heavily from this design, but ending at the front windshield and have the side bars being able to bolt in and out for rego. (I know, that compromises the design, but its all a trade off) and having only a single cross member in the roof and having the rear of the cage welded to the chassis at the rear instead of the strut tower.

I would love to hear what you think Mick, I know you mentioned the rules, but at this stage, thats beyond the scopre of where ill be with the car in the next few years.

By the way, shot Sean a message about which SLR kit to grab for this build.
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      07-26-2019, 06:33 AM   #4
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I would suggest looking at the rule book of any potential series you might one day run. They usually have an extensive section on cage requirements, this should help you with the basics... (tubing size, chromoly / mild steel, required layout,...). If you are going for a weld in cage, I would bring the car to a reputable gage guy in your area and work with them on a design.

The cage shown, looks like it’s missing a bar that goes cross the front in the dash area and you might look at tying in the diagonal bars going to the shock towers to the gage.

A good cage can make a real difference on how the car handles.
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      07-26-2019, 08:24 PM   #5
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Well, first of all, I'm not a fan of a prefab cage. This one in particular. I see many issues with this cage. I feel you would be better off finding a good cage designer/builder and working with him on what you want. There's no reason you can't design a cage that can be added to later if you do decide to go racing. Too many cages I've seen over the years have bars that serve no purpose. Clearly added by people who don't understand the physics involved. More bars mean more weight. The E86 is also a very stiff/strong chassis. What is needed in an E46 may not be needed in an E86 for example (such as footwell protection). My particular cage is designed to be added to later if I choose. Perhaps take a look at it again and see if you gain any ideas.

A caged car should not be driven on the road. They are meant to be driven while you're wearing a helmet. Car interiors are designed with soft head friendly materials. Cage bars aren't.

Installing a full cage is very invasive. Best done when the car is stripped down to the bare chassis. More so than a half cage.

I sense you are eager to make more modifications such as the wide body kit and now a cage. If you really think you will go racing in the near future, be mindful of the rules. If you really just want to build the car for fun (which I totally get) and see where it goes, than design a cage (full or half) that you feel comfortable with and don't get hung up on what a "proper" cage looks like.
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      07-27-2019, 01:09 AM   #6
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Thanks Michael, appreciate the comments, you too Booker.

The reason for trying to square s cage away atm is because my car will be in pieces anyways, which will mean easier access. Aside from that there is no rush, hell there is no rush anyways as the car wo t be going in for surgery for at least another 2 months. So I have plenty of time to square a good design away.

Yep, I think I will just get together with my mate Immi, and have a chat with him and see what would be good. Leaning towards a simple design, using t45 steel, which is lighter/stronger. I had a really simple roll over bar, that I did love a lot, however now the bulkhead is coming out, I'll need to come up with a different solution.

Any good pics of your cage hanging around Michael?
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      07-27-2019, 10:06 AM   #7
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Cage designs differ for many reasons that you need to consider.
1. Chassis design - this will dictate what is needed and how to make it fit. Two seaters like the Z4 and Miata/MX5 often need the main hoop to terminate on the shelf behind the driver. Structurally, it's a better place to terminate the main hoop and also may be needed to set the main hoop behind the driver.
2. Rules - rules obviously have a great impact on ones cage design...if you're going racing.
3. Anticipated use and risk tolerance - There does not exist a safe cage. More cage is not necessarily safer. Dale Earnhardt died because NASCAR chassis' are too rigid. Energy absorption is key to survival. Defeating engineered crumple zones can make the car less safe. Having bars run through the firewall to the front strut towers is a good example of this. This is done to stiffen a chassis at the expense of safety (also note that there is no requirement to run bars through the firewall in CAMS). So there is definitely a balance. Understand what you are trying to accomplish before you simply build a birdcage in your car.

Looking at the CAMS cage rules, they look pretty reasonable. The amount of cage depends on the class you plan to run. But looking at the rules, I think it would be pretty easy to build a modular cage that can be added to later. Mine would definitely be easy to make compliant. The only issue may be the main hoop not coming down to the floor behind the seat if I need to add more door bars. I suspect I could add a plinth behind the seat. My cage builder told me this was not an issue as he's done this before and builds cages for SCCA, NASA, and BMW CCA compliant cars.
https://www.cams.com.au/docs/default...sn=7721ed27_10

Of course I have pics of my cage:

Easier to see raw without paint from the cage builder. Note that rather than run the down bars to the frame rail, we brought the frame rail up to the down bars by building the box (aka, plinth) that also serves to create a structural mounting point for the shocks for the option to use coilovers. This also makes a good mount point for a strut bar and diagonal in the downbar plane. Looking at the robust C pillar and roof structure, we felt is wasn't needed on this chassis, but could easily be added if required by rules.


The seat is bolted to the cage for additional structure.


Personally, I'm more terrified of side impact than rollover so we added a single diagonal door bar terminating into a plinth that can be used for the front hoop if added. A single diagonal door bar doesn't impede ingress/egress. BMW Club Racing here in the states only requires a single door bar (most run more). It looks like CAMS also only requires one depending on class.




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      07-28-2019, 11:03 PM   #8
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Thanks Micheal, I contacyted my mate Imi, who used to build cages for Subaru Rally Australia, and hes put me in contact with one of his mates over here in dxb (who also builds/welds a lot of cages), and is providing the cage details and works for his mate to weld, bend and install my cage.

Very simple design, borrowing very heavily from yours lol. more as a 1/2 cage, which can be added on later on. Thanks for the info about the front bars not being required. Thats gonna be lighter. a few other bits not added as not required my mate recons.
The price is a bit higher than i would have liked though. More info when i sit down at the table with the installer.

That cams document is a pretty darn interesting read, very easy to understand and makes good sense.
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Last edited by Vanne; 07-28-2019 at 11:21 PM..
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      08-10-2019, 11:21 PM   #9
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Hmm, well this is going differently. The cage i am looking to add was going to add in another 50kgs or so. Thats WAAAAYY to heavy for what i am looking for. Have decided to modify my current setup. The goal for this project is going to be LIGHT... not going to buy a freaking CF kit and then still come out heavier after installing a huge cage. And as you pointed out Michael, this is a track car, not a full on racing car. If it does turn into that later, changes will be made.

Thanks for making me see that difference mate, think i had poo in my eyes for a bit there.

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