Roll Cage design questions.
 

I'm finally getting to the point on my rally car project where I need to start figuring out the design for a roll cage. My only problem is I don't really have the knowledge to design a "safe" cage as per FIA and NASA rules, I can follow their guidlines just fine, but I would rather find either an engineering firm or an experienced builder to help with the design process.

Do any of you race guys have suggestions as far as cages go?

I've looked at these cages but they are impractical for rally cars because there is no area for the codriver to sit in.

Scott could design one thatll accomodate your needs Im sure.

Thanks for looking! Take a look at my actual cages though. Pull the Petty bar out of the design and there's plenty of room. In fact, even with the Petty bar, I can have a passenger in my car for open track days, but I wouldn't suggest it for a rally car. Put a double diagonal, a harness bar and you'd have a fairly good rally cage.

I've actually been looking at your cages for a couple months now, ever since my original post in the 1st gen section when I was given the link.

That link I threw up in the above post of mine was just the one that was in my clipboard when I hit paste.

Something like the image below is what I was thinking of for both driver and passenger sides, that is if it isn't too hard to get into/out of for a big guy :(.

http://www.izzyscustomcages.com/imag...Downbars01.JPG

what's the rules on the rally cages?

The base cage +2 looks like a totaly fine design.

Mount the main hoop to the rear subframe, shoot the rear downtubes to the strut towers.

The other way to go is to gut the doors and install nascar door bars rather than the X's used with that cage. Gives you move elbow room, and if you get hit in the door, the bar is farther away.

I'm 5 10", 270 lbs, and that would be totally easy to get in and out of. It's when the bars reach the top of the doors that it starts to get tricky.

Good luck.

The rules on the rally cages used to just follow the SCCA rules, but now with rally not being backed by SCCA, it falls to the NASA rules. Or I could go with the CARS rules, but they are all pretty much the same.

I've got a bunch of full size pics of my cage here: http://www.headonphotos.net/Paul

sweet.

Thank you :bigthumb:

Make sure all of your tubes lead directly to other tubes if at all possible. Imagine the load paths as you design it. Use string and tape to mock up the main tubes. On the doorbars... if you make them enter into the doors, be sure that you keep the horizontal bars as \_/ shaped as possible. Try not to S either end as the first bend will be the weak point. With a \_/ bend the loads in a side impact (TREE!!!) will be sent directly into the Main hoop and downbars/crossbar.

Run a "Kneebar" between the two front downbars. This bar is critical in a side impact. X diagonals inside the main hoop with X bars added to the rear hoop braces will work wonders. You can put your harness bars on either set of X bars, just remember to keep the harness' as short as possible... less stretch. If you go with snap hook harness' keep the mounting on the seat side of the harness bar, not the back side of the bar. In a head on, tabs mounted on the back side can pull over the bar and loosen up the harness.

Straight bars transfer loads, bent bars act as springs.

I'm sure there's more... but that's enough for now.

There are many, many good tips and photographs in Herb Adam's book "Chassis Design." It costs less than $20, and will be well spent money.