Cage design review

[ScotcH]

Hey all,

Here is a cage design that seems perfect for my needs (Solo 1, lapping, racing). Can those in the know provide some feedback in terms of safety and stiffness? Also, any issues with legality in the various series (TGT, OCC, FAQ)? Thanks!

[Dave]

Driver's side NASCAR style door bars would be a good addition, IMO. I believe CASC-OR's roll cage section recommends (but doesn't require) them. Check the regs to be sure. Appendix O, I think.

[CobraStang]

If I look at that drawing a little cross-eyed, I can see a dinosaur! :D

[slucas]

That looks like a good solid design.Have you calculated the weight yet? You may have more rear caging than you need
or want, but that depends on the car. If you are left hand drive
I would suggest moving the "halo" diagonal to the opposite diagonal to give you more head room.

[malcolm]

I'm not an expert on the subject, but I would just make a little change to the front of the cage at the top. I would replace your small bar (shown in red, not sure if you would intend that to be in tension or compression), with the the bar it seems to intersect.

edit: I don't think you need that cross-brace in the bottom behind the hoop. I would put it at the top, or even just run one diagonal.

I also included nascar-style bars, because I think it would be silly to race a car without them. :rolleyes:

[ScotcH]

Originally posted by slucas
That looks like a good solid design.Have you calculated the weight yet? You may have more rear caging than you need
or want, but that depends on the car. If you are left hand drive
I would suggest moving the "halo" diagonal to the opposite diagonal to give you more head room.

Excellent point about the halo bar. As for the weight, not yet, but some of the added bracing (like the X as the back) is stiffness in addition to safety :)

[ScotcH]

Originally posted by malcolm
I'm not an expert on the subject, but I would just make a little change to the front of the cage at the top. I would replace your small bar (shown in red, not sure if you would intend that to be in tension or compression), with the the bar it seems to intersect.


Seems like that might make getting in/out a pita ... I'll have to test it out.

Originally posted by malcolm
edit: I don't think you need that cross-brace in the bottom behind the hoop. I would put it at the top, or even just run one diagonal

In the BMW, this add ALOT of stiffness, and the center of gravity is low. I don't need it, but the stiffness is worth it (according to BMW guys anyway!)

Originally posted by malcolm
I also included nascar-style bars, because I think it would be silly to race a car without them. :rolleyes:

Yeah, this seems to be the way to go. However, for that I would need to scrap my door guts and get some lexan windows. Not quite at that prep level yet, but we'll see.

[sparky]

Hey Scotch, if you need someone to bend the tubing or fabing the whole cage, i can help you out. PM me if intrested:)

[Do It Sidewayz]

here's what i'd delete from your cage....and next picture will be what i'd add in place of it.

I'm not 100% familiar with the race cage rules...but i know the rally cage rules fairly well..as i just did the cage in my rally car myself.

anyways.

In your main hoop, you have all your x-bracing and harness bars...I'd move this all into your backstays...including the harness bar...i know in the rally book it's a no-no to have your harnesses mount right behind your seats...you need some stretch in your belts.. if you look at most if not all pro built rally and race cars. the harnesses always mount as far back as possible. this also allows you as much room to mount your seats as possible....and alows alot more open space inside the car...along with less tubes to whack your head off of.


You have x-bracing going from the bottom of the main hoop to the bottom of your back stays...if you move your x-bracing and harness bar from the main hoop to your back stays this isn't needed...and is just extra weight...and cost.


You have a bar connecting the middle of your main hoop with the bottom of your back stays.....this is not needed...the bar going from the bottom of the hoop to your backstay mounting place is more than enough.

The "top of a-pillar bar" which just bridges the corner....it won't do much for you...this is probably the weakest point of any cage...what you need to do is run this basically straight down, and join with your door bars or your lateral roll bar mounting location.

[Do It Sidewayz]

now for what i'd add/replace with.

First starting at the back....as i said above...move the x-bars into the backstays, and install harness bars at the required height.


The "top of a-pillar bars".....this is a better way of doing it...however it will make entry into the car a little tougher


Now what to add.

i would highly recommend running a "sill bar". Have this bar run directly along your rocker panel, and weld in a few spots. Have the bar "hockey stick" into the lateral bars and the main hoop, This puts the bar under compression and very strong.


In your main hoop...run a bar from the junction of the top door bar on the main hoop down to the tranny tunnel, and install a plate on the tranny tunnel...Do this on both sides....however make it out of 1 piece with a bend in the middle....install a plate on the tranny tunnel, and weld the bar to it.



To change slightly....for the door bars...most people when doing "x-bars" will run one continuous tube from the top to bottom, then have 2 half bars to form the other half of the "X"....make these out of 2 continuous tubes...if you have a 30 or so degree bend in each bar you can construct a top and bottom half.....when you notch the tubes to meet the main hoop and lateral roll bar....have the bars "clocked" slightly so the bends are the furthest point out, and almost touching your inner door skin.. This then puts both bars under compression. Where the two bars join, weld the tubes together....then plate both sides.

[Do It Sidewayz]

sorry pic didn't work.. we'll try this

[rmicroys]

By the rules you MUST have a main diagonal in the main hoop.

[Do It Sidewayz]

ah..ok.. the Rally rules say it can be in either the main hoop or the back stays.

[ScotcH]

Thanks Chris ... good points, but some do not apply:

- the harness bar must be very close to the seat back to use with a HANS device (5" I believe)

- running bars to the tanny tunnel will make it illegal in SCCA, NASA, and BMWCCA (except for modified classes). Not a huge deal, but I'd like to keep the car legal in as many sereis as possible

- I like the down bars from the top of the A-pillar, but I'll have to test to see if this is possible in my car (for getting in and out, and mirror obstruction)

I love slow days at work ... Here is an revised design, based on feedback (thanks all!) The jury is still out on the X location ... bottom, middle, top. BMW guys seem to say bottom for stiffness. Maybe 1 diagonal on top is a good compromise?

[John Powell]

Arek. You have a PM.

[malcolm]

yeah, I would want the belts to be mounted as close behind the seat as possible so they don't stretch as much under load (and if you've seen some inboard footage of rally crashes in particular, they stretch a LOT).

just my thought though. :)

[DEK]

There is some info that says shoulder harnesses can stretch 15%.
A very long belt that becomes 15% longer won't be holding you very well in the seat. This isn't bad in a single impact crash (how rare is that) but in a multiple tumple crash the driver is not going to be very well restrained after the first impact.

[Mike Basden]

I hate to add my comments to this and muddy the waters even more, but here are a few changes I'd make:

1) The angle of your A pillar support is wrong. It should support the A pillar and halo in the event of roll over (compression). Do a Nascar style support by using it as a big gusset from about mid A pillar vertically down to the sill bar. This will give you the strength you need but not handicap you for ingress/egress. Do a similar bar on the passenger side. Which brings me to my second point.

2) If you are reluctant to do Nascar style door bars (God only knows why...) at least add in a full sill bar with vertical support through the center of the doors (sill bar to lowest door bar or frame) to strengthen it should a t-bone occur. Also weld a plate to the external side of the door bars (Harold Fair plate) to prevent debris and/or the other vehicle from encroaching into the driver compartment. This plate should be welded from the mid point of the bar or more. Do not just cut a plate to fill the holes and weld it in between the door bars!

3) You can shorten the gusset on the B pillar but make sure it is at a true 45. This support is just meant to try to maintain the 90 degree angle to the halo in event of roll over. Since it ties into the halo and X brace, you don't need it to be a structural piece, just a support.

4) The brace from the passenger B pillar to the driver backstay should also be present from the driver B pillar to the passenger backstay (full X brace). They way you have it will still allow for some chassis flex and doesn't provide enough support to the passenger side backstay.

5) The sill extentions to the backstays (middle bars) don't add any support; only weight. I don't see any reason why these should stay.

Bottom ine is, do't try to re-invent the wheel when it comes to this. A lot of peope have crashed before you and these designs have been proven to work. Stick with what works, and your car will be safe. If in doubt look for pictures on the web from reputable chassis builders and copy their ideas. Or better yet, if you have the money pay someone who is knowledgable and does good work to build you a suitable cage.

Just my 2 cents,
Mike