JMortensen Posted November 25, 2006 Share Posted November 25, 2006 OK, so if you followed this thread: http://forums.hybridz.org/showthread.php?t=106457 you can probably guess where this is going. I want to tie the rear suspension pickups into my rollcage. The suspension pickup points are just to the sides of the tunnel in the back. I want to add a couple bars from the main hoop to the strut towers, and I also wanted to do an X from the strut tower to the bottom of the hoop on the opposite side like this: I'm thinking that this is a lot of weight back here, and maybe ultimately unnecessary. So in the interest of making the installation simpler, I've come up with another idea. I'm thinking that it needs some help though. It just doesn't look right to me, and I want to be sure I'm doing something worthwhile before I start notching tubes and welding things in permanently. So here's the pictures of the back of the car (blank slate in case anyone wants to sketch their better idea--hint, hint). So here's my idea. Make something of a triangle from the hoop to the strut tower, the tower down to the suspension pickup point (through the rear deck), and then back to the hoop. The main issue I think I'll have here is that the hoop is leaned back a lot for maximum head clearance, so the bar going from the hoop down to the suspension pickup wouldn't be the same left and right. On the right side it would have to intersect the diagonal in the main hoop, and from the inside of the diagonal it would have to then head in a more rearward direction to hit the spot on the floor. I don't know that this is particularly bad other than aesthetically. The other issue is that this idea doesn't tie the right and left sides together. So while the main hoop and the strut tower bar would connect the two sides, all of this other stuff wouldn't, which is I think a problem from a stiffness point of view. OK, here goes. Anyone have a way to make something salvageable out of this mess??? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 25, 2006 Author Share Posted November 25, 2006 Thought this other picture would help too. My kinda crappy idea, tried to fix with a bar across the trans tunnel (this doesn't look like the answer to me): The X and a brace from the hoop to the floor: This just looks like too much to me, the X with the triangle design together: Quote Link to comment Share on other sites More sharing options...
katman Posted November 26, 2006 Share Posted November 26, 2006 Put a horizontal in the main hoop at the kinks and forget about everything else. Not worth the weight. What you so far have looks great, BTW. Quote Link to comment Share on other sites More sharing options...
260DET Posted November 26, 2006 Share Posted November 26, 2006 How about looking underneath with a view to reinforcing the suspension pickup points there and tieing them in with other under floor structural members, such as the rails. You may then be able to go further and tie into the bits you have already reinforced as shown in the pics. I would not be adding too much more metal though. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted November 26, 2006 Share Posted November 26, 2006 Jon, This goes back to your recent thread on the LCA vs the strut taking the moment load but IMO the inner LCA pivot takes very little vertical load so I dont understand why you need to tie into there? The load path seems to be along the floor fore/aft and side to side. I'm thinking about puting a big X connecting the two subframe connectors together underneath and doubling as a trans mount to help distribute those loads assuming I have the load path correct. If your running any door bars and even if you are not I've alway thought it was a good idea to tie the kink in the main hoop into the rear tower to help distribute t-bone loads but that's just looking at the load path and no direct experience. Edit - I just saw 260DET reply while typing this and he's basically saying what I'm saying. Cameron Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 26, 2006 Author Share Posted November 26, 2006 The area of stronger, reinforced metal where the bearing holders are attached to my early Z car is actually very small. It only extends maybe 1" on each side beyond the area where I've welded in the bearing holders on the bottom, and then it also attaches to the reinforced area in the trans tunnel as well. To the sides of the bearing holders the frame rail changes, and goes from .108" thick to .035" thick (guessing on the thinner stuff, but it is sheet metal thin). This small area of the chassis isn't only subjected to side loads, it also handles all of the upwards torque from the nose of the diff as it tries to lift. I have an alternate diff mount, but it still puts that torque into the chassis through the diff crossmember, and that means directly through the bearing holders. I suppose I could have done the Ron Tyler diff mount, but I've already put a lot of time/effort into the one I made previously, and don't just want to switch it out now. The point is, there really is a lot of upwards stress on the chassis right there. What I'm really worried about though is the fact that with NO rubber in the suspension there will be NO damping of any shock loads going into the chassis. That's why I'd like to make this area as stronger. I've already redesigned the uprights in the back to make them stronger, and the footprint of the uprights is probably 300% larger than the original design, so I'm hoping that will keep things intact in the back. I would like to do something to prevent damage in the front here as well. If the supports from the main hoop were straight up and down, that would mean that they would not be terribly good at dealing with side loads. They're not, though, and by coming in at a 45 or so degree angle they should be able to handle some side loading with too much trouble. For these braces I'm going to use 1.625 x .065 tube, which is about 1.1 lb/ft. So while I will be adding weight, and I'm trying to figure out the most efficient use of that weight, it won't be as bad as the main cage structure which is 2 lbs/ft. Lastly, I do think there is some value to adding more support back here. I'm going to be running some extremely heavy spring rates, taking a cue from those wackos down in Oregon... They seem to be having really good luck with spring rates over 500 in/lbs, so I'm expecting that I'll probably start out somewhere in that range. Not to mention I'll be on very wide slicks. If I use the previous slicks I was using, they're basically 10" wide, but I may go wider than that. I haven't decided yet. All of this translates into some pretty severe loading of the chassis, and that's why I'm looking to do all of this seemingly unnecessary support structure in the back. I'm not averse at looking to the bottom of the chassis to see what bracing can be done there as well. In fact I'll probably run out there and take a couple shots just to get an idea of how I could brace to the SFCs on bottom as well. I had already planned on welding gussets in the corners of the frame rails, and between the frame and rockers as well. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 26, 2006 Author Share Posted November 26, 2006 You can see from this picture where the strong part of the frame rail ends: I suppose I could run a small piece of tube or a gusset from the SFC to the bearing holder area here. I don't think I'd physically have enough room to weld it in all the way around. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted November 26, 2006 Share Posted November 26, 2006 Jon, This goes back to your recent thread on the LCA vs the strut taking the moment load but IMO the inner LCA pivot takes very little vertical load so I dont understand why you need to tie into there? The load path seems to be along the floor fore/aft and side to side. I'm thinking about puting a big X connecting the two subframe connectors together underneath and doubling as a trans mount to help distribute those loads assuming I have the load path correct. If your running any door bars and even if you are not I've alway thought it was a good idea to tie the kink in the main hoop into the rear tower to help distribute t-bone loads but that's just looking at the load path and no direct experience. Edit - I just saw 260DET reply while typing this and he's basically saying what I'm saying. Cameron Jon, I have to agree with cameron, from and engineering standpoint, you overkilling something that's already dead as far as the rear struts are concerned. Meaning there is no live loads there to distribute that you haven't already accomplished. Doc Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted November 26, 2006 Share Posted November 26, 2006 Jon: how about a single tube on each side from the tunnel area that you wish to reinforce up to the main hoop at approx. 45 degree angle? (in the plane of the main hoop) That shouldn't add to much weight with the tube you describe. With the cross bar between the towers and the braces from the top of the main hoop down to the towers, I think that area should be already plenty strong. (no expert though) Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 26, 2006 Author Share Posted November 26, 2006 Well I suppose just in terms of mounting everything in a stronger way just welding the plate to the floor and plug welding to the bottom would make the control arm mounts less likely to tear out. Maybe I should just do that and then concentrate on the X... Quote Link to comment Share on other sites More sharing options...
johnc Posted November 26, 2006 Share Posted November 26, 2006 BRE made a diff mount similar to the Ron Tyler style and then run a vertical bar front the top center of the mount up to the harness bar/diagonal in the main hoop. Something similar would probably be all you need to handle any loads from the forward LCA mounts. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 26, 2006 Author Share Posted November 26, 2006 I don't suppose there is a reason why that BRE idea couldn't be done this way... Quote Link to comment Share on other sites More sharing options...
JustinOlson Posted November 26, 2006 Share Posted November 26, 2006 Here are my 2 ideas: Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 27, 2006 Author Share Posted November 27, 2006 Thanks for those Justin. There will definitely be a shoulder bar across at the kink. I have been waiting to get a tubing bender for that one. I need the bender because the brace behind the driver's seat needs to bend back to allow the seat to slide all the way back. I just had a tubing bender delivered, but they sent the wrong one. The second picture with the straight bar all the way across the bottom is a good idea, and I had that option when I put the control arms together, but opted against it just because I didn't want to have to try and remove the original frame rails and then have to build another front diff mount. It might have been the "best" answer, but I just didn't want to have to hassle with it. The bar from the top of the hoop to the back corner is something that I've seen in older racecars and on some Japanese cars, but it's purpose is the same as the diagonal bar in the main hoop, mainly to keep the hoop from folding in the event of a rollover. So that one is a bit redundant. The ^ from the shoulder bar down to the control arm mounts is a possibility. Quote Link to comment Share on other sites More sharing options...
tube80z Posted November 27, 2006 Share Posted November 27, 2006 The ^ from the shoulder bar down to the control arm mounts is a possibility. Another option would be to turn this V into a X by hooking into the struts. This should make everything stronger. And if you really want to make it work run a bar straight forward from this intersection to the front V from the strut towers. If you make a balsa model you'll see this causes a lot of improvement. Personally, I don't think the floor area needs the V and you'd be better off with a wide, low X as you have in your first pics. That is unless you decide to go with the single tube forward to the front of the car. And don't forget underneath the car as others have mentioned. If you can hook the rails to the rockers and close sections of the tranny tunnel with an X it will improve the stiffness. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 27, 2006 Author Share Posted November 27, 2006 Think I have it. The tunnel is already reinforced in this area, so I think this will work. Weld the plates in on the floor to strengthen the mounting to the chassis as originally intended. Run a small 1x1x.063 square tube gusset from the floor to the side of the tunnel. Do the X as I had previously intended. Also added in the shoulder bar in blue just to clarify the plan there. Quote Link to comment Share on other sites More sharing options...
johnc Posted November 27, 2006 Share Posted November 27, 2006 Not to discourage the creativity here, but is all this bracing really needed? The chassis is seam welded and you've reinforced a lot of areas on the car already. It seems that a good diff/front crossmember mount would be more then enough. Again, not to discourage anyone's efforts, but sometimes when we have extra roll bar tubing and a new tubing bender, every problem now needs a new roll cage segment. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 27, 2006 Author Share Posted November 27, 2006 I've been pretty well set on doing Cary's X design for a long time. He and I have discussed it at some length via email, and he's done some modelling of various different designs and found that it really made a big difference in the stiffness of his models. With the spring rates and tires I intend on running I think it's going to be worthwhile. I figure for ~10' of tubing at about 1.1 lb per foot for this thin walled tubing, it's going to be worth it. I didn't really feel like I was doing the right thing on this control arm stuff, which is why I wanted to get more opinions from everyone. But I do feel my latest idea comes with an absolute minimum of weight added and should keep the control arm mounts from tearing out. I'm looking at doing a pretty thorough cage, and at this point my goal is not to leave any stone unturned. I'd rather overdo it now that the thing is on a rotisserie than underdo it and have to tear it all apart again. Quote Link to comment Share on other sites More sharing options...
tube80z Posted November 27, 2006 Share Posted November 27, 2006 Will you have a cage and door bars? For some reason I thought you'd only have a roll bar in the car. If that's the case I think you can drop the bars that go from the shoulder bar kink back to the strut. I think those are to tie into door bars more than anything else. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 27, 2006 Author Share Posted November 27, 2006 No, you convinced me to do a full cage. The original plan was to do a bar, but now I'm going for broke. Quote Link to comment Share on other sites More sharing options...
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