Hey all,

I just acquired a 95 M3 for a dedicated track car. I am in the process of working out a cage design, and I've been reading a lot, and looking at many designs. I think I have a good idea of what I want, and I understand the reasons behind the design (triangulation, loads, etc.). At this point I am only doing the back half since I need to keep the car on the road for a while. The design is is pretty basic: Main loop, diagonal, and harness bar, an X from the main loop base to the rear somewhere, and diagonals from the main loop (top na dbottom) to the ends of the X. I was contemplating adding an X on top as well, but I'm not sure how this will impact visibility, and if it adds anything. I am basically taking a lot of ideas from this thread: http://forums.bimmerforums.com/forum/showthread.php?t=257181&page=3&pp=25&highlight=cage+design

Here are couple of questions that maybe some of you can answer:

1. For the rear points, should I use the shock towers, or the main bulkhead (right above the wheel welll)? I don't plan on running true coil-over, but maybe the next owner? If I do run it to the bulkhead, can I efficiently tie in the shock towers later on?

2. Is there any point in adding a tie bar between the shock towers, then triangulating with the spring mounts (through the body floor)? How much work is this for the welder (not me!)

3. Is dropping the main loop through the floow the best way to do the top welds, or have most of you simply done it by acrobatics?

4. Can you forsee any issues with adding the front half later on? The only thing I can think of is that if the main loop is close to the roof, it might be hard to weld the main side bars at the top.

5. Do any of you tie the diff mounts into the cage? What classes is this legal for in the US (In Ontario, it's wide open, so I'm not too concered ... again, possible resale issue)

6. 1.75x.095 or 1.5x.120 ... any reason to shoose one over the other? The 1.75 is lighter, but the 1.5 is easier to bend. Anything else?

I just had a cage built by TC Design www.tcdesignfab.com

Tony has many pics on his sight, including my car, from which you could get ideas.

Some of the concerns you have will affect what class your car falls into. Whether you race it or want to plan ahead for the next buyer, you might want to become familiar with some of the class rules.

Mine is 1.75 x .095 DOM.

Jay



Hey all,

I just acquired a 95 M3 for a dedicated track car. I am in the process of working out a cage design, and I've been reading a lot, and looking at many designs. I think I have a good idea of what I want, and I understand the reasons behind the design (triangulation, loads, etc.). At this point I am only doing the back half since I need to keep the car on the road for a while. The design is is pretty basic: Main loop, diagonal, and harness bar, an X from the main loop base to the rear somewhere, and diagonals from the main loop (top na dbottom) to the ends of the X. I was contemplating adding an X on top as well, but I'm not sure how this will impact visibility, and if it adds anything. I am basically taking a lot of ideas from this thread: http://forums.bimmerforums.com/forum/showthread.php?t=257181&page=3&pp=25&highlight=cage+design

Here are couple of questions that maybe some of you can answer:

1. For the rear points, should I use the shock towers, or the main bulkhead (right above the wheel welll)? I don't plan on running true coil-over, but maybe the next owner? If I do run it to the bulkhead, can I efficiently tie in the shock towers later on?

2. Is there any point in adding a tie bar between the shock towers, then triangulating with the spring mounts (through the body floor)? How much work is this for the welder (not me!)

3. Is dropping the main loop through the floow the best way to do the top welds, or have most of you simply done it by acrobatics?

4. Can you forsee any issues with adding the front half later on? The only thing I can think of is that if the main loop is close to the roof, it might be hard to weld the main side bars at the top.

5. Do any of you tie the diff mounts into the cage? What classes is this legal for in the US (In Ontario, it's wide open, so I'm not too concered ... again, possible resale issue)

6. 1.75x.095 or 1.5x.120 ... any reason to shoose one over the other? The 1.75 is lighter, but the 1.5 is easier to bend. Anything else?

1) I personally belive you shoud use the main bulkhead if you are only using one rear point. It's more structural and it alllows the cage to be "wider" which should improve overall chassis rigidity. It also allows for more triangulation along the sides and better load path transfer from the front to the rear. Of course, if you are in an unlimited cage type situation, you can use both points and tie into the rear subframe/diff (see #5 below).

2) Not much of one. Plus, it instantly makes your chassis illegal for most club racing classes here in the States...leaving Modified class as the only option.

5) We do, but it's only allowed in the top class (Modified) of BMW CCA racing. You can do solid subframe and diff mount bushings that will help a lot. Actually tying the subframe into the cage will limit what the car can be used for in the future.

Referring to Bryan's answer to #2. You can tie the shock towers together in BMWCCA Prepared. But, you can't tie that to the spring mounts or diff mounts.

That's how I had Tony do mine. It's being set up for IP.

Jay

Yeah, sorry I didn't make that clearer.

I was contemplating adding an X on top as well, but I'm not sure how this will impact visibility, and if it adds anything.

Shouldn't need an X. One cross bar will suffice without the extra weight of the X. Another area you might pay attention to the supporting the A-pillar bar with gussets and additional bracing...a lot of rigidity can be gained there.

I'd suggest waiting until its a FULL dedicated track car, or you are going to club race it. Then have the cage built as best it cna to fit into your class/rules.

It'll save money in the long run and allow you to run the safest possible configuration(and help with chassis rigidity as well).