roll bar design question

[dfink]

I am in the process of designing a roll bar for my 85' cab. I have decided to do a bolt in as I am just looking for some extra protection at DE and don't plan on ever actually racing so no need to meet any bolt in standard. I am thinking of a DAS style bar with mounts at the seatbelt in front and the seat back in rear. The rear mount bolt is so small though that I am looking at other mount location. Options are as follows.

1: Relocate the rear braces to the rear seat belt mounts.
a: advantage larger bolt
b: disadvantage not as good of an angle

2: Make the rear mount as normal but extend the angle iron to span the seat bolt and the belt mount
a: advantage maybe stronger - not sure but might help with rearward movement in an accident.
b: disadvantage weights more and might not add any strength.

3: make bar as usual but have the cross braces go to the rear seat belt mount instead of the bottom of the rear brace.
a: advantage not sure but potentially stronger due to six bolt places instead of four.
b: disadvantage wieghs more and cross brace might not be as strong since it doesn't go back as far.

Let the debate begin. Sorry for the smilies was just putting in a colon outline style I have edited them out.

[dfink]

bump once.

[Joe Bob]

Design and function may be an issue if it's not approved by the local race body.

Best to go with a known design......just my two cents.

[ted]

Originally posted by dfink
I am thinking of a DAS style bar with mounts at the seatbelt in front and the seat back in rear.

FYI in our PCA TT series the bolt in DAS bars are no longer allowed.
I think the reason was that the single bolt roll bar mounts could shear on impact.

Check the AX forum for more discussion on Roll bars.

[Joe Bob]

Here's mine....built by a San Diego area welder that does production and is supposed to be built to SCCA specs...

Currently on eBay...

I will settle for an occasional AX....too much family committment.

Bolts to the floor and wheel wells with scab plates underneath.

[dfink]

I did here that the DAS bar is no longer accepted in So Cal. I don't plan on running any sanctioned TT just for my own increased sense of safety as I run the local track now with nothing. I can see the point on the small 8mm rear bolts shearing hence the attempt to improve the design. I would think it would be next to impossible to build a commercial bolt-in that would exactly hit all six bolts but it can be done with the four points. Since we are building this from scratch the mounting points can be bolted in then spotted

I think I like the six point idea with the cross braces bolting to the rear seat belt mounts. The rear down tubes bolting to the seat back bolt and the front bolting to the front seat belt mount. With this in mind are the opinions the relocation of the cross braces (2) would help or hinder the strength.

Also is there anywhere that there are success stories of a roll bar actually helping. I would think about anything with any strength at all would help in a simple roll over. Start flipping and I don't think even the best roll-bar would help. Would need a cage for that. Any pictures on how a roll-bar holds up in a roll-over. Again I know that everything is relative a full welded in cage would be best but will the bolt in design help.

[gduke]

What track to do you want to run your car on? I'm from IA and also own a cab.... will be taking the car to Kelly-Moss Motorsports in Wisc. to have other work done and will be talking to them about roll bars and stiffening up the chasis.

Eventhough mine seems fairly stiff, I haven't AX'ed it because I don't want to twist the chasis.

Gary

[84CAB]

Not to hijack the thread but Gary be sure to let us know what your shop says about stiffing the chassis and a rollbar -I have been researching this myself.

[dfink]

I run at Midamerica Motorplex Glenwood Iowa. I don't think you should worry about twisting the chassis doing an auto-x. My cab body anyhow is very stiff already at least for a cab. I can jack it from the jack point and do not get any discernable deflection of the body. Can open the door crawl in a bleed the brakes and still no change in door gap that I can tell. I don't think a roll bar is going to help stiffen things much. Maybe a full cage that was built right but the bar only covers 2' of a 13' car so I don't think it does much for twisting. I have auto-crossed mine for 3 years and about 1000 track miles and body is still happy as far as I can tell. I have not changed the rear sway bar and upon inspection during tranny rebuild this winter they showed no sign of visable fatigue. Tranny rebuild was a precaution not a nessecity but if you auto-x cross watch that first to second shift.
In any case I am sure a welded in cage is better than a four point bolt in roll bar but in a cab if it doesn't skewer you it should help some in a roll over. I don't expect it would do much in a high speed end over ender. The vulnerablility of the 8mm rear seat bolt is why I am looking for opions on other attachments points. For those who are not following my proposed design it would attach just like a DAS bar. Would have 2 cross braces instead of one that went from the top bar to the rear seat belt mounts. So the system would bolt at 6 locations instead of 4.