Roll cage 'petty' bar - advice sought

campbellcj · 02-11-2006, 03:18 PM

POC has a rule against passengers (instructors/students) riding in the car if there is a cage tube crossing their 'space'. Apparently there was a fatal crash years ago where contact with this type of bar was deemed to be a factor, so they are not at all flexible on this rule.

Sooo...my choices are to either make it removable, or just ditch it entirely.

Will making it removable negate the extra stiffness added by this bar? If so then I wouldn't bother. In that case, what is the best way to remove a welded bar like this? I sure don't want to have to redo a significant portion of the cage. Is it OK to just cut it out and then grind down the welds?

I am kind of inclined to just ditch this bar and perhaps add some more tubing to the chassis & pickup points to add more stiffness. In the POC points-based classification system this is only 1 pt IIRC and I think I can 'afford' it class-wise.

Car is a 914-6 (conversion) with a welded 8pt 1.5" DOM mild steel cage built by TonyC (http://www.tcdesignfab.com)

Any advice appreciated.

greglepore · 02-12-2006, 07:33 AM

To answer question one, yes, you can just cut it out and grind down the welds. As to the first question, I'd want the existing cage tied into the footwells or firewall. Also, you'd want a diagonal brace in the rear hoop is it doesn't have one b/c of the petty bar. That setup, along with a GT stiffening kit and maybe some long reinforcement, will be stiff enough.

My car is a 73 tub, cage is tied into car at belt points on targa bar and at footwells. It has a gt kit in the rear, and braces running from rear suspension console to rear firewall. No petty bar. Door gaps are very stable even when car is lifted from a single point. Is it as stiff as with a petty bar? I don't know, but it plenty stiff for tt and ax, and the passenger seat is usable.

Making it removable is an option, if you were to use joints like those shown in the SCCA GCR you'd likely not lose stiffness.

campbellcj · 02-12-2006, 12:35 PM

Thanks for the reply Greg. I posted the same topic at 914club.com also and it the concensus so far is the cage should be fine w/o the extra bar. It is already tied to the footwalls and the rear hoop is triangulated. So I'm just going to cut out the petty bar and not hassle w/ making it removable.

911scmedic · 02-12-2006, 01:30 PM

I'm just trying to understand which bar your talking about? In the pictures on your link to TC Designs the 914 passenger bar goes from the shoulder (B -pillar) to the floor (A -pillar) downward. Is this is the bar your talking about? If it is - the current POC rules (Appendix D: Last paragraph) "Passenger side bars are highly recommended".

Before you go cutting something out I'd have it looked at by one of the POC tech stations for verification...Could be wrong, but my car is V4 with a full cage "x" braced at the passenger door and I've never had a instructor say "no way".

Cause if you use the wording to the "T" your knee bar (and mine) cross "through their space" ...

Might want to throw this question to the POC site too!

Doug

greglepore · 02-12-2006, 02:00 PM

A "petty bar" runs from the main hoop, usually near the drivers right shoulder, down to the floor, usually near the passenger's feet. It really stiffens the car fore and aft, but is a hazard to even a restrained passenger.

911scmedic · 02-12-2006, 03:43 PM

I'm with ya on that...but his pictures show side intrusion, which would increase passenger safety.

Possibly the terms Petty bar(as you describe) and NASCAR bar(s)(which is side door intrusion) are being transposed.

I was just trying to help

Doug

911scmedic · 02-12-2006, 03:50 PM

No Petty bar here.

campbellcj · 02-12-2006, 09:11 PM

I found a pic that shows the bar I'm talking about. It is the one that goes diagonally from the rear upper hoop to the passenger footwell. (This is my car just as the cage was getting finished up.)

rfn026 · 02-13-2006, 11:05 AM

Here's some real solid information about cages.

http://www.ces.clemson.edu/~lonny/pubs/journal/sae983053.pdf

Richard

jluetjen · jluetjen's Garage

That's an excellent paper. The important thing to take away from it is not which bars that they added or removed, but the process that they followed to develop and modify their model.

It's possible to do something like that for one of our Porsches using shareware FAE software like Grape. If you knew what you were doing it would take maybe a week of dedicated time. Add in extra time to brainstorm solutions and stuff and you're up to maybe a couple of weeks. If you're a novice like most of us and working in your free time I figure that it would take a couple of months to work through the learning curve and then the development process.

Without doing that, it's not clear to me what conclusions you could draw.