Gruppe

There has been some posts and such by some guys building or thinking of building race cars on what design cage to use. I have gotten the nod of approval from the SO for this on my otherwise JP 325 and am wondering what the optimal rear tie in points for the 6+2 cage are. Recently there was a cage that had a cross bar between the shock towers that had the rear downtubes mounted to it. I talked to that guy and he sent me the pics of another car with the same design. It works but there was some dissent on weather it was optimal. Where would you mount the rear downtubes on a 92 with the stock rear bulkhead still in place and the springs in the stock location? Any of you engineering types that have those neat programs that can draw this out for me on a real picture would be greatly appreciated.

Thanks

Ryan

PS 16x8 ET37 BBS track wheels FS

rear bulkhead and be done with it, there was a thread a while ago with some awsome designs in it that will work for prepared class cars

Can't go wrong with the shock towers. Here's a picture of mine.

There is a question though since the springs are in a different place - there is obviously the opportunity for some twisting between the spring mounting point and the shock mounting point but that section of the chassis seems very stiff and I doubt if there's a difference on a prepared class car with DOT tires, etc.

In a mod class car you'd want to go to both, and then also down to the diff mounting points....

-Mike

First of all, it makes a difference whether or not your car is a 2 door, a 4 door with fold down seats or a 4 door with a bulkhead.

I agree with Mike that the shock towers is arguably the best place, even though I have my cage welded to the top of the subframe.

I would like to point out however, with no offense to Mike or his cage, that configuring as shown in his picture can prevent from getting a logbook in many organizations.

The rear supports should mount directly to the shock tower (with a mounting pad) and all crossbraces should then be mounted to the supports. I have seen a car be denied a logbook (in NASA of all places) because the rear supports were welded to a rear crossbar, and not to the chassis as specified in the rules.

SCCA sez, and NASA coat-tails:
"The main roll hoop shall have two braces extending to the rear attaching to the frame or chassis"

Good point Jay, I've heard firsthand of a similiar situation in SCCA. Doesn't seem to be a problem in BMW CCA, as many BMW cage builders take a similiar approach.

I dont think I have seen a prepared cage that did not do it this way. Anyone have a pic?

Scho - As I alluded to on the TWS thread, it doesn't seem to be a big deal in BMW CCA, as the rules are very, very non-specific on cage building. In fact, they are almost non-specific to the point that a pretty unsafe cage may fit within the wording of the rules. Not to mention that you could really take advantage of some performance increases if you are building a car for BMW CCA...just as an example off the top of my head, there's no limit to the size of backing plates you are allowed to use.

I don't have a picture handy, but the downbars just terminate into the shock tower and then the cross braces are attached to the downbars. It definitely puts a more appropriate load on the welds and backing plates to do it the way that SCCA requires.

When I had my cage done, Tony (TC Design) specifically asked me if I wanted to be legal in SCCA ITS. If so, he would have not tied to the top of the shock towers. I don't have a pic handy, but mine is done like Mike Gilberts. BMWCCA legal, but not SCCA.

Jay

My question is as follows: in the original post it is stated that his springs are in the stock location. I am going to ASSUME that he means that he will not be running a full coilover rear set-up. For this reason (here comes my lack of comprehension) why would he want to tie to the rear shock towers versus the subframe mounting points or the bulkhead.

Thanks for the help. Obviously cage building for me is left to the experts for a reason.

For this reason (here comes my lack of comprehension) why would he want to tie to the rear shock towers versus the subframe mounting points or the bulkhead.

Given the lack of a rear coilover, I would tie to the bulkhead because of the triangulation you are able to accomplish between the B pillars and the bulkhead, as well as the load paths you can create all the way from the front +2 mounts all the way to the rear bulkhead. Others prefer the shock towers. Outside of actually testing chassis rigidity, we are all just guessing to a point.

Going to the "subframe" location is impossible to do legally in IT/Prepared anyway, as it would require the removal of some sheet metal to actually tie into the metal that the subframe mounts to.

My question is as follows: in the original post it is stated that his springs are in the stock location. I am going to ASSUME that he means that he will not be running a full coilover rear set-up. For this reason (here comes my lack of comprehension) why would he want to tie to the rear shock towers versus the subframe mounting points or the bulkhead.

Thanks for the help. Obviously cage building for me is left to the experts for a reason.

In my case, I knew I wasn't interested in ITS and was building a car for Prepared with the possibility of going to coilovers someday if I decided to move up to Mod. And, to be able to tie into the subframe or diff mounts without too much trouble. I didn't spend a whole lot of time going over pros/cons, but went with the recommendation of my cage builder.

Jay

Yeah NASA gave me a fit over it one time!!!! However with the cheif of tech we came up with a very simple solution and added two triangular brackets/braces behind the horizontal bar between the shock towers. Now it is NASA/SCCA legal.

The only reason I would not build an IT cage this way (to the rear shock towers) is to pick up some of the spring forces better.

Here is a bad pick of the two little braces/brackets/plates.

Pic (http://www.tcdesignfab.com/Billym3-01.jpg)

Gruppe

In these two pics that were posted both were on cars without a rear bulkhead. Another poster said it depended on weather it was 2 or 4 doors and weather it had the bulkhead or not. Mine is a 92 E36 4 door with the bulkhead still in place. One said for prepared they would go to the bulkhead and be done with it. This car will not be running ITS. Plans are for CCA prepared, NASA GTS Challenge, and maybe PBOC if the weekend was right. Thanks for the input.

Ryan Brenneman

First of all, it makes a difference whether or not your car is a 2 door, a 4 door with fold down seats or a 4 door with a bulkhead.

So what is the consensus?

Here is a pic of my cage, 4 door w/bulkhead. You may want to consider building a cage that is ITS legal in the event you ever sell your car. The more places that is can be raced will make it more sellable....

good luck



Gruppe

In these two pics that were posted both were on cars without a rear bulkhead. Another poster said it depended on weather it was 2 or 4 doors and weather it had the bulkhead or not. Mine is a 92 E36 4 door with the bulkhead still in place. One said for prepared they would go to the bulkhead and be done with it. This car will not be running ITS. Plans are for CCA prepared, NASA GTS Challenge, and maybe PBOC if the weekend was right. Thanks for the input.

Ryan Brenneman

Here is a pic of my cage, 4 door w/bulkhead. You may want to consider building a cage that is ITS legal in the event you ever sell your car. The more places that is can be raced will make it more sellable....

good luck

I assume this is a picture of the cage not finished...?

I assume this is a picture of the cage not finished...?

Obviously...

It was work in progress. I don't have any of it complete/painted, but here are a few more...

I assume this is a picture of the cage not finished...?

Nice, just checking ;)

When you are ready for that Aim system you inquired about, let me know.

Goodluck and keep us updated with your car buildup.

Thanks, I'm still looking at my stock dash, so don't worry! ....car is done, I just don't have any recent pics. My motor decided to go at the last race, so that is what I'm working on now....New motor should be in this week. I will be at VIR in a few weeks for the BMW race. Is there going to be anyone with the AIM up there that you know of?

Thanks!!!

Nice, just checking ;)

When you are ready for that Aim system you inquired about, let me know.

Goodluck and keep us updated with your car buildup.

Hmm, possibly, not sure.

Were you looking at the MXl or Xg Log?

That is exactly the shot I needed. I knew some cages were tied in there from talk and some unclear pictures but your picture makes it very clear. That is where I want to put my rear mounts. Some people will say that precludes SCCA but that is ok. Between CCA, NASA, and maybe some PBOC I will get all the racing I can afford. And this car goes away when it has turned its last wheel in fun and can turn no more. To quote the SO "You better like that car cause you are not going to do that to another one..." And when it does finally reach the great racetrack in the sky I will do the smart thing and buy someone else's finished racecar. Hopefully that is a long way off. Thanks all for the input.

Ryan

Glad I was able to help out. My cage is SCCA legal, so with that you can race anywhere u want...

good luck!

-scott

That is exactly the shot I needed. I knew some cages were tied in there from talk and some unclear pictures but your picture makes it very clear. That is where I want to put my rear mounts. Some people will say that precludes SCCA but that is ok. Between CCA, NASA, and maybe some PBOC I will get all the racing I can afford. And this car goes away when it has turned its last wheel in fun and can turn no more. To quote the SO "You better like that car cause you are not going to do that to another one..." And when it does finally reach the great racetrack in the sky I will do the smart thing and buy someone else's finished racecar. Hopefully that is a long way off. Thanks all for the input.

Ryan

Is it clear for rally ;) Too bad no more scca pro rally, there was some cool events.

If I am not mistaken, dont the CCA rules state that you can have the main hoop mount to the rear shock mounts/towers, and may pass through any bulkhead separating the passenger compartment from the trunk area, so long as the bulkhead/panel is sealed around where cage passes through?

Now I dont know if it would be any use or be advantageous to have the cage "mounted" at both, but maybe you could get the best of both worlds sorta (triangulation and 'picking up' rear suspension movements)? Not sure if the meaning of that rule applies to the actual bulkhead, or just the paneling that cars without fold-down rear seats have.

I dont know....someone who knows more than I do should go ahead and set me straight on this one :stickoutt

Now I dont know if it would be any use or be advantageous to have the cage "mounted" at both, but maybe you could get the best of both worlds sorta (triangulation and 'picking up' rear suspension movements)? Not sure if the meaning of that rule applies to the actual bulkhead, or just the paneling that cars without fold-down rear seats have.

You couldn't actually "mount" the bar in both places or you would have too many mounting points in your cage and be bumped to modified class.

The bar can pass through the bulkhead, but it can't be welded to it if the bar continues on to another mounting point in the trunk.

There really aren't any rear suspension movements to pick up in the rear in Prepared class. You can't legally remove the metal needed to get down to the spring or subframe mounts, and there is little to no stress on the shock towers when you aren't running a true coilover. If you ARE worried about the shock towers, I'm almost positive that you can legally add a stress bar in Prepared class.

Ha yeah the number of mounting points is simple enough to make it illegal...didnt think about that.

Thanks for the info.