lbhsbZ Posted January 29, 2007 Share Posted January 29, 2007 I searched, but this was not covered. I have a buddy that gets me autopower cages pretty cheap, so I didn't think anything about it and ordered one up. I was very happy with the autopower I got for my VW, but not so sure about the Z cage. I picked it up last night and started welding the main hoop in today, then I stopped. I don't like how the main hoop anchors to the wheel wells. I'd much rather it went all the way to the rockers. This would also give me a much better place to attach the rear of the door bars. I have 2 options at this point. option 1. Mount the hoop as it was intended to the fenderwells, then run another tube down to the rocker (where a proper main hoop would be attached) and tie it into the existing main hoop right above the mounting point on the fenderwell. If I did this, I would tie in a couple of diagonals from the lower mounting points that tie into the cross tube right at the middle of the car above the tunnel. option 2: Make the main hoop legs longer by butt welding extra lengths of tube to it after properly prepping/beveling the joint, grind the weld, then hammer on a 6 inch long sleeve and welding the ends of the sleeves (the next size up DOM tubing fits nice and snug), so that the but weld is right in the middle of the 6 inch sleeve. I don't plan on ever dealing with the SCCA, so legality is not an issue. The series that I race in will approve of this design. As far as I'm concerned, this sleeve extention should make the tube stronger than it originally was, because now its essencially twice as thick, but I may be wrong. Either way, I don't feel safe doing 150+ on a road course with curbs and walls without something tying into the rocker. I'm trying to make this work because it would cause problems should I try to return it and get my money back. I think I should go with option 2, because it would be stronger and require about 10 feet less tubing than option #1. Your thoughts please. Quote Link to comment Share on other sites More sharing options...
johnc Posted January 29, 2007 Share Posted January 29, 2007 Install the cage as supplied by Autopower. Yes, it would be better if the main hoop went to the rocker panels, but that's not how they designed it. The modifications you mention would not be legal for most race sanctioning bodies and there's a good chance they will not let you run. Quote Link to comment Share on other sites More sharing options...
hotimport Posted January 29, 2007 Share Posted January 29, 2007 Yeah i have heard about this before with the Autopower cages. Oh well thats just the way they make them. How much did you pay for youre cage? Its the bolt in version right? Quote Link to comment Share on other sites More sharing options...
jmark Posted January 29, 2007 Share Posted January 29, 2007 Try this thread. http://forums.hybridz.org/showthread.php?t=117721 Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted January 29, 2007 Author Share Posted January 29, 2007 I saw that thread. That just tells me what I already know...that the cage is of a poor design. I spoke with them this morning and they make a full main hoop for the 2+2 that can be modified to fit in the Z. I should have it by tomorrow, so I'll post some pics of the fitment. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted January 30, 2007 Author Share Posted January 30, 2007 Install the cage as supplied by Autopower. Yes, it would be better if the main hoop went to the rocker panels, but that's not how they designed it. The modifications you mention would not be legal for most race sanctioning bodies and there's a good chance they will not let you run. Did you read my original post? I said that legallity of the cage is not a concern. I don't race with NASA, I don't race with SCCA, I race in Mexico with Caldera Promotions, and I've discussed the issue with the race tech inspectors, and since it makes a stronger tube than a one piece tube, they will allow it. Safety is my concern, not whether or not it meets the rules of organizations that I don't wish to be involved with. My question was about down which road I should go. I don't care how autopower designed it..I feel its a crappy design that could be easily improved on....drastically. They want both the main hoop and the rear bars to connect about 8 inches apart on the same piece of sheet metal fenderwell. The rear bars are supposed to act as braces and strengthen the main hoop. I doubt much strength can be gained by this rear tube design. What about a side impact? Do you think that the autopower design is better than my modified design? I think that the rocker box is considerably more stout than the inner wheelhouse.......on account of it incorporating more than 1 sheet of material in its design. After I welded in the main hoop as supplied by autopower, I could grab it and flex it about a 1/2 inch forward and backward. This is not a good foundation to build a rollcage that must support a 2500lb vehicle. Hell, the sheetmetal destorted as the bolts were tightened on the original 4 point bar. Just because someone designed something (and I use that term loosly) to work in a certain manner, does not mean that it is correct, nor does it mean that the design is not open to refinement or improvement.....thus the reason none of us are happy with the way that nissan designed our cars, and why we are all making them better. I've been reading posts on this board for a long time, and most of them are very in depth and technical, there is also a lot of excellent ideas and design work here. I guess I expected a more in depth answer than you gave me. I'm sorry if I offended you. Anyway, here's how it worked out: I ended up having autopower build me another main hoop to my specs after making some measurements and realizing that the "legs" of the current main hoop are not perfectly parallel, but about 5 degrees away from each other. Had I installed extensions, they would be to far out to attach to the rockers. Thanks for your insight though. Quote Link to comment Share on other sites More sharing options...
johnc Posted January 30, 2007 Share Posted January 30, 2007 Did you read my original post? Yes I did. Good luck. I've been reading posts on this board for a long time, and most of them are very in depth and technical, there is also a lot of excellent ideas and design work here. I guess I expected a more in depth answer than you gave me. I wasn't offended at all. You seem to have a chip on your shoulder and are upset because I didn't post a lengthy response to your question. Sorry. You're ultimate solution is the correct one and I'm glad it worked out. Your original options were really stupid ideas and I, as a SCCA tech inspector, SCCA and NASA driving instructor, and fabricator wouldn't ride in your car on a track if I saw those mods to the roll cage. They are unsafe and were outlawed decades ago by SCCA, NASA, NASCAR, NHRA, etc. None of the race sanctioning bodies (except VARA and HSR West, and only then if its got papers) that I know of and have built roll cages for would allow the modified roll cage you planned on doing with your two options. That should tell you something significant about the safety concerns. That you found some sanctioning body somewhere that might have let you run with the cobbled together mess you were planning to do does not make things safe. There you go - you've got your more lengthy response. Luckily Autopower stepped up and provided you with a main hoop more suitable for your needs. FYI... the roll cage rules put out and enforced by race sanctioning bodies are not there to make things difficult for the competitors. The rules exist to make things safe for the competitors and there are decades of high speed crashes that prove the safety of the designs. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted February 1, 2007 Author Share Posted February 1, 2007 No chip on my shoulders....not at all. I'd just like to hear technical reasons why extending and sleeving a roll cage tube would be wrong or unsafe. "Because the rules say you can't" are not good enough reasons. I am making this post rather than letting this thread die because maybe I am wrong....and if thats the case, and someone can explain why, I will gladly accept understandable constructive critisizm and rethink the way I design structural modifications, not just cages, in my racecars. I was under the impression that this type of modification would make the tube stronger than it was originally, in which case there should be no harm in doing it. If I am making the structure weaker and failure prone, I need to know that and I need to know why. If I'm wrong, please tell me why. PS: Autopower failed to step up and solve the problem in a timely manner, so I am doing this on my own. I've placed an order for a ProTools bender, and will be bending up a proper cage for the car.....pending feedback that I receive here. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 1, 2007 Share Posted February 1, 2007 Sleeving a tube introduces a stress riser at the weld. Loads imparted into a tube will concentrate at the stress riser and the unsleeved part of the tube will fail where it meets the sleeved part. You're correct in stating the sleeved part of the tube is stronger then the rest of the tube, but that doesn't mean the entire tube is stronger then before. The loads are not spread through the part in a uniform manner. They get concentrated at a point and that concentration will most likely cause the tube to fail at less of a load then if the stress riser didn't exist. The fundamental reason a roll cage works on a unibody car is because it transfers load throughout the structure. Loads input into the unibody or a cage member get transferred to other cage members and other points in the unibody. No one point receives all the load. Race sanctioning bodies specify one continuous tube for the roll cage main hoop to eliminate stress risers that can cause the main hoop to fail. The main hoop is the primary load transfer member in a roll cage and if it fails, loads concentrate at the point of impact. Most other bracing members in a roll cage transfer their loads into the main hoop. An on track accident is rarely just one impact. A poorly built cage can protect the driver from one hit but it will most likely fail in the process. A subsequent hit will leave the driver unprotected at best and, at worse, the failed cage is now debris or sharp projections inside the car increasing the driver's injuries. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 1, 2007 Share Posted February 1, 2007 BTW... you might want to come down to my shop. I have a customer's Vintage racing 240Z in here that has an Autopower wheel well mounted roll bar that's been modified to be a roll cage. Its not the best design in the world but VARA and HSR West have allowed the car to run. It also ran with SCCA decades ago but was made illegal in the early 1990s. I'm adding an additional door bar and a knee bar to the cage. http://www.betamotorsports.com Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted February 1, 2007 Author Share Posted February 1, 2007 Thanks John, that was the response I was looking for. Now I understand. Are you at the shop on the weekends? I might be free saturday to swing by. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 1, 2007 Share Posted February 1, 2007 I'm usually working on Saturdays. This Saturday I will be here from 8am to 10am and then off to do some work at a friends shop. Next weekend I'm out at Cal Speeday at the autocross and later the Redline Time Attack. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted February 1, 2007 Author Share Posted February 1, 2007 I'll try to make it out there Saturday morning.....I can't to any more work to the car until my bender arrives anyway....so I've got my weekends free for a while. Quote Link to comment Share on other sites More sharing options...
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