Z4 M Coupe Cage Designs

[crfine88]

I have drawn up three cage designs and would like to hear comments and feedback. For reference I used the "ROLL CAGES FOR GT AND PRODUCTION BASED CARS" section of the 2011 SCCA rules. I am only building the back half of the cage, but want to leave the option open for a full SCCA spec cage in the future.

All three of the cage designs protect both the driver and passenger based on the rules found in the 2011 SCCA rule book. The differences between the three cages are weight, rigidity and cargo room.

1st cage:This cage is a replica of the one Z4mnyc built in his car. This cage would offer the most rigidity (best for handling performance).
Approximate weight: 51.0 lbs


2nd cage (LTR):This cage would add some rigidity with the x brace connecting from each side of the top of the main hoop to the bottom of each rear brace.
This design also offers better access to cargo space.
Approximate weight: 38.0 lbs


3rd cage (LTC):I do not believe this cage would add any rigidity. It would fulfill the needs for safety and provide the most cargo room.
Approximate weight: 40.0 lbs


As of now, I am leaning toward option number 2 (LTR). This cage is the lightest of the three. This cage will provide the safety I am looking for and provide more rigidity than stock. This cage also provide better access to cargo space which is a consideration since the wife and I take the car on road trip a few time a year.

I appreciate any insight, comments and feedback you may have

Thanks
CF

[nmulax]

You know I have zero engineering knowledge... so no idea on how accurate my assumptions are .
BUT what about something like this? In theory it should be lighter than the 1st and 3rd, provide more rigidity than the 3rd, and provide some ease for luggage access.

Could be combined with the front part of any cage.

- adam

[onelove]

I would probably go with Cage 1.

The diagonal bar on the front portion of the cage provides support in the event of a roll over for the main hoop from collapsing in a downwards motion from the top.

Cage 3 does this as well but it's likely a bit of overkill on this portion of the cage vs. the rear which has limited uprights supporting the main hood. You do benefit from more cargo space, but at a sacrifice of being less rigid.

Cage 1 does the best job of supporting the cage from collapsing, while providing an adequate area to attach your belts. It also provides a bit more structural rigitity with the bar going from tower to tower, a feature i really like.

[Serious]

Can I give you some honest advice?

Buy a real race car, don't half ass turn a street car into a race car over a period of 3-4 years. All you will end up with is a car that won't be good for any series and you will spend double the amount you already have into it to make it compatible once you finally want to go racing for real, and even then you will quickly come to the realization that there is no affordable series for a car like a z4M and you will sell it to buy a spec miata/spece30/pro3 car.

Also realize that with that cage you will effectively be killing the resale value on a $30,000 car. $30k goes along way in buying a proper prepared racing car.

I have less that $4,000 total into my 635csi racer, nearly all of it in maintenance and safety equipment. On the track with proper tires it eats modified street cars for lunch while being far safer and almost zero financial risk if you ball it up.

[nmulax]

Originally Posted by Serious

Can I give you some honest advice?

Buy a real race car...

You realize (excluding vehicles coming from the factory non street-legal) all "race cars" started life as street cars that somebody took the time to convert for track use. His goal right now isn't a track only vehicle. Who are you to dictate what vehicle someone chooses to use? With that mindset you yourself would be better suited to get a Miata or E30 over your 6er.

And nothing he's EVER done to his car has been "half-ass" .

[boondocksaint]

^Post before this.

Track days for a street car.

Races for a race car.

Just my $.02 and in no way a judgment.

And we realize that street cars become race cars, man. But if that's the ultimate goal, it's way cheaper to just buy a race-prepped car in the long run.

How many people have you seen sell a race car at a huge loss? There's a reason for it. We're not deciding or damning anything or anyone. We're trying to give an honest assessment. Jumping all over us for it is kind of you, though.

[crfine88]

Originally Posted by nmulax

You know I have zero engineering knowledge... so no idea on how accurate my assumptions are .
BUT what about something like this? In theory it should be lighter than the 1st and 3rd, provide more rigidity than the 3rd, and provide some ease for luggage access.

Could be combined with the front part of any cage.

- adam

I could do that with the front part of 1 and 3. In 2 the tubing from the top of the main hoop has to connect to the bottom of the rear braces per the rules. This would definitely allow Rena to bring her huge suitcase

Originally Posted by onelove

I would probably go with Cage 1.

The diagonal bar on the front portion of the cage provides support in the event of a roll over for the main hoop from collapsing in a downwards motion from the top.

Cage 3 does this as well but it's likely a bit of overkill on this portion of the cage vs. the rear which has limited uprights supporting the main hood. You do benefit from more cargo space, but at a sacrifice of being less rigid.

Cage 1 does the best job of supporting the cage from collapsing, while providing an adequate area to attach your belts. It also provides a bit more structural rigitity with the bar going from tower to tower, a feature i really like.

Thank you for the feedback. Can I bug you for a little more; I want to make sure I am on the right track here.

The SCCA rules states, "Main hoops shall incorporate a diagonal brace. The brace shall either be in the plane of the main hoop, or extend from the top of one rear brace to the bottom of the opposite rear brace." In cage 2 the diagonal braces from the top of the main hoop to the bottom of each rear brace fulfill this requirement. In cages 1 & 3, the diagonal braces inside the plane of the main hoop fulfill this requirement.

All that being said and with your experience, do you think that the diagonal brace inside the plane of the main hoop provides more support in the event of a rollover than the diagonal brace from the to top of the main hoop to the bottom of the rear brace?

Thanks again,
CF

[crfine88]

Originally Posted by Serious

Can I give you some honest advice?

Buy a real race car, don't half ass turn a street car into a race car over a period of 3-4 years. All you will end up with is a car that won't be good for any series and you will spend double the amount you already have into it to make it compatible once you finally want to go racing for real, and even then you will quickly come to the realization that there is no affordable series for a car like a z4M and you will sell it to buy a spec miata/spece30/pro3 car.

Also realize that with that cage you will effectively be killing the resale value on a $30,000 car. $30k goes along way in buying a proper prepared racing car.

I have less that $4,000 total into my 635csi racer, nearly all of it in maintenance and safety equipment. On the track with proper tires it eats modified street cars for lunch while being far safer and almost zero financial risk if you ball it up.

I understand where you are coming from, but have different mindset with this build. If this were going to be for track only, I would have started with a different platform (e36 M3).

Originally Posted by nmulax

You realize (excluding vehicles coming from the factory non street-legal) all "race cars" started life as street cars that somebody took the time to convert for track use. His goal right now isn't a track only vehicle. Who are you to dictate what vehicle someone chooses to use? With that mindset you yourself would be better suited to get a Miata or E30 over your 6er.

And nothing he's EVER done to his car has been "half-ass" .

Thanks Adam,
You get it.

Originally Posted by boondocksaint

^This.

Track days for a street car.

Races for a race car.

Just my $.02 and in no way a judgment. It is your car. We're just trying to look out.

Thank you for your $.02. That's what the forum is all about

[Serious]

Originally Posted by nmulax

You realize (excluding vehicles coming from the factory non street-legal) all "race cars" started life as street cars that somebody took the time to convert for track use. His goal right now isn't a track only vehicle. Who are you to dictate what vehicle someone chooses to use? With that mindset you yourself would be better suited to get a Miata or E30 over your 6er.

And nothing he's EVER done to his car has been "half-ass" .

I don't think you understand the point of my post.

Street cars on a race track are all half assed. period. When you run on street tires with street brakes and 400+lbs of interior/AC etc you are running a compromised setup.

Also I was just trying to give some honest advice because I have seen many people waste tens of thousands of dollars on mods into street cars before realizing what they actually want to do is to go racing.

My advice is before doing something irreversible like installing a half cage into an expensive car is to sit down and actually write out the financials and clearly think what you want to be doing with the car 3 years down the road. The way I see if you truly want to go racing you have a $30,000 car with $30,000 worth of mods, that 60k will buy you a spece30 and two full seasons of racing or a street car converted race car someone put $150k into that is worth 50k now like this:
http://cgi.ebay.com/ebaymotors/2007-...item3f0a33595a

http://cgi.ebay.com/ebaymotors/Porsc...item25643791c5

or for $80k you can buy this ferrari racecar:
http://cgi.ebay.com/ebaymotors/2001-...item2a10f6b232

http://cgi.ebay.com/ebaymotors/05-Po...item2c5cf6fee1

or if you actually want to go fast for real.
http://cgi.ebay.com/ebaymotors/New-M...item2c5cfdbed3

I hope my post is more clear now, it's really easy to have a car with $100,000 into it and have it only be worth $20,000. Take advantage of other people builds and either buy something prepared or build a car for a specific series from the get go.

[Serious]

Originally Posted by crfine88

I understand where you are coming from, but have different mindset with this build. If this were going to be for track only, I would have started with a different platform (e36 M3).

No offense but once a car has even a half cage in it, it is track only. It's dangerous to drive it on the road, and you will have a hard time reselling.

[The HACK]

I'm about to give some very opinionated advice here. Take it with a huge grain of salt.

If your plan is to go racing, you will never be able to sink enough money into the MZ4 Coupe to make it truly competitive in just about any sanctioning body. It's the same reason why you don't see a lot of very successful E46 M3s competing in SCCA/NASA/BMW CCA CR. For whatever reason, they typically class this motor/chassis against some very unfavorable competition. While I applaud the effort to try and polish turd (not saying the MZ4 Coupe is a turd, but the situation that this chassis is classed in for amateur racing is), I feel, in my personal opinion, that the MZ4 Coupe is best served as a weekend "racer," or if you MUST go competing in a sanctioned body, the most favorable one for it would actually be BMW CCA CR because you'll be up against the likes of other S54 engined MZ3, E46 M3s, and/or 135i where the chassis can be quite competitive.

If you do not plan on going racing and is just doing this for the fun of it...Heck, even if you're going racing for realz, I would skip the half cage build and go straight to full cage. It just never really made any sense to me why anyone would just put in half a cage (*cough* Porkchop Marketing *cough*) and not bother with the most important part of the protection...For the driver. Especially on a chassis as stiff as this car, going with a half cage really isn't going to gain you any significant improvement in chassis rigidity and really the cage is mostly for PROTECTION purposes.

I'm not an engineer by any stretch of the imagination so I'm not going to comment on the cages...But if you're going to the extent of work to put in a cage, I would think doing it once rather than multiple times will not only aid your sanity but also give you an overall BETTER car to use on the track.

Oh and I would just pick up an E36 M3 to build if I were building a track only car. Just as rewarding to build AND potentially more fun to compete in. There's very little H-Stock and H-Prepared action in BMW CCA CR, and you'd most likely be placed in C-Mod with your mods which will mark you at the back of the pack anyway.

[crfine88]

Originally Posted by Serious

No offense but once a car has even a half cage in it, it is track only. It's dangerous to drive it on the road, and you will have a hard time reselling.

No offense taken. I appreciate your feedback.

Originally Posted by The HACK

I'm about to give some very opinionated advice here. Take it with a huge grain of salt.

If your plan is to go racing, you will never be able to sink enough money into the MZ4 Coupe to make it truly competitive in just about any sanctioning body. It's the same reason why you don't see a lot of very successful E46 M3s competing in SCCA/NASA/BMW CCA CR. For whatever reason, they typically class this motor/chassis against some very unfavorable competition. While I applaud the effort to try and polish turd (not saying the MZ4 Coupe is a turd, but the situation that this chassis is classed in for amateur racing is), I feel, in my personal opinion, that the MZ4 Coupe is best served as a weekend "racer," or if you MUST go competing in a sanctioned body, the most favorable one for it would actually be BMW CCA CR because you'll be up against the likes of other S54 engined MZ3, E46 M3s, and/or 135i where the chassis can be quite competitive.

If you do not plan on going racing and is just doing this for the fun of it...Heck, even if you're going racing for realz, I would skip the half cage build and go straight to full cage. It just never really made any sense to me why anyone would just put in half a cage (*cough* Porkchop Marketing *cough*) and not bother with the most important part of the protection...For the driver. Especially on a chassis as stiff as this car, going with a half cage really isn't going to gain you any significant improvement in chassis rigidity and really the cage is mostly for PROTECTION purposes.

I'm not an engineer by any stretch of the imagination so I'm not going to comment on the cages...But if you're going to the extent of work to put in a cage, I would think doing it once rather than multiple times will not only aid your sanity but also give you an overall BETTER car to use on the track.

Oh and I would just pick up an E36 M3 to build if I were building a track only car. Just as rewarding to build AND potentially more fun to compete in. There's very little H-Stock and H-Prepared action in BMW CCA CR, and you'd most likely be placed in C-Mod with your mods which will mark you at the back of the pack anyway.

Thanks Hack,
I have gained a great deal of information from you posts on many topics. I consider you one of the better sources for information on this forum.. Thank you for your feedback here.

I wanted to go with fixed back seats and harnesses, so a roll bar was needed. I know I do not "need" most of the stuff on my M coupe. This is a hobby for me. I do research each modification extensively before adding it to the car, but this is for fun. At the end of the day, there are many cars better suited for racing for all the reasons you stated above.

I don't have any plans for racing the M coupe (I do think TT would be cool once I improve my skills). My goal is to build a bad ass street/track M coupe (when I say track, I mean club driving and not racing). As mentioned above, I agree with you; If I was building a racecar, I would have started with and e36 M3. The main reason I am using the SCCA specs is make sure I build something safe.

Thanks again for your feedback. I respect the straight forward approach on all topics.

CF

[onelove]

Originally Posted by crfine88

All that being said and with your experience, do you think that the diagonal brace inside the plane of the main hoop provides more support in the event of a rollover than the diagonal brace from the to top of the main hoop to the bottom of the rear brace?

Thanks again,
CF

Past experience in drag racing says yes. that being said the short answer it that doing both is better than doing one or the other.

As far as the other discussion, ultimately not everyone's goal is to go directly into racing. I still enjoy weekends out with friends at DE's or private track rentals just as much as wheel to wheel racing. The Z4M is a phenomenal car for driving schools. In the long run building a car, going through the headaches, and learning what respective suspension,tire compound and set changes do as you go in driving schools is one of the best ways to get into racing and have an understanding. It's an expensive lesson, but sure beats 10-15 weekends of race car rentals to get your feet wet and learn to drive a car at it's limits. I have plenty of racer friends who now own race cars, but still keep their "hybrid" track/street car around for those times when they need to get on track and their race car isn't ready. As far as resale value is concerned, half cages can be removed, or a buyer can be found whose looking to buy the car for the same purpose, track driving.

I think the poster isn't as crazy for putting a backhalf cage into his car with fixed seats and harness as the many other people driving these cars at 9/10s on track with a factory seatbelt and no hans. I unfortunately put myself into that group of knuckleheads but plan on following a similar path soon.

[Serious]

one last thing OP if you absolutely certain this is something your going to do may I suggest a bolt in design? It's going to be a lot easier to remove in the future and the performance difference is negligible.

[z4mnyc]

Originally Posted by crfine88

I don't have any plans for racing the M coupe (I do think TT would be cool once I improve my skills). My goal is to build a bad ass street/track M coupe (when I say track, I mean club driving and not racing). As mentioned above, I agree with you; If I was building a racecar, I would have started with and e36 M3. The main reason I am using the SCCA specs is make sure I build something safe.
CF

Nice work Chris, thanks for posting this thread. I have the same goals for the car and I agree with what others said in terms of building a proper race car.

[crfine88]

Originally Posted by onelove

Past experience in drag racing says yes. that being said the short answer it that doing both is better than doing one or the other.

As far as the other discussion, ultimately not everyone's goal is to go directly into racing. I still enjoy weekends out with friends at DE's or private track rentals just as much as wheel to wheel racing. The Z4M is a phenomenal car for driving schools. In the long run building a car, going through the headaches, and learning what respective suspension,tire compound and set changes do as you go in driving schools is one of the best ways to get into racing and have an understanding. It's an expensive lesson, but sure beats 10-15 weekends of race car rentals to get your feet wet and learn to drive a car at it's limits. I have plenty of racer friends who now own race cars, but still keep their "hybrid" track/street car around for those times when they need to get on track and their race car isn't ready. As far as resale value is concerned, half cages can be removed, or a buyer can be found whose looking to buy the car for the same purpose, track driving.

I think the poster isn't as crazy for putting a backhalf cage into his car with fixed seats and harness as the many other people driving these cars at 9/10s on track with a factory seatbelt and no hans. I unfortunately put myself into that group of knuckleheads but plan on following a similar path soon.

Cage design: That logic works for me, better to be safe than save 12lbs. I will go forward with cage 1. Thanks again

Other topic: You understand where I am coming from

Originally Posted by z4mnyc

Nice work Chris, thanks for posting this thread. I have the same goals for the car and I agree with what others said in terms of building a proper race car.

Again, thank you for leading the way on this whole project.

[BookerM3]

I would suggest option 2 with the diagonal brace in the main hoop. The
diagonal brace makes the cage much safer for the driver in a role over.

As for the other comments made on the topic of transforming a Street car
to potentially a racecar over time, its is much more expensive. You end up
replacing the same parts over and over again as you car transforms to its
final stage. This said the journey is a great learning experience.(especially
if you do much of the work yourself)

As for make the Z4M competitive, anything is possible with enough money,
time and effort.

[johanness]

Has it occurred to any of you nay-sayers that Chris is doing all of this to garner the experience and end up with an exceptionally unique and superfine ride? I'm sure the cost of doing this doesn't keep him up at night, and I'm pretty positive he couldn't give a rats-ass about re-sale or penny-pinching. If so, I'm sure he probably would have went down the stereotypical race-build of an E36 or Miata. If you still question why he's doing this and suggest these rides... then you've totally missed the point.

I say go for it. Your car is already one of the nicest around on these forums, and will continue to be the standard set for a lot of people. I'm sure what you end up with will give more than enough people a wicked run for the money, while maintaining a one-of-a-kind feel.

And don't mention Porsches around Serious, as it will derail this entire thread.

[Swashplate]

Originally Posted by johanness

Has it occurred to any of you nay-sayers that Chris is doing all of this to garner the experience and end up with an exceptionally unique and superfine ride? I'm sure the cost of doing this doesn't keep him up at night, and I'm pretty positive he couldn't give a rats-ass about re-sale or penny-pinching. If so, I'm sure he probably would have went down the stereotypical race-build of an E36 or Miata. If you still question why he's doing this and suggest these rides... then you've totally missed the point.

I say go for it. Your car is already one of the nicest around on these forums, and will continue to be the standard set for a lot of people. I'm sure what you end up with will give more than enough people a wicked run for the money, while maintaining a one-of-a-kind feel.

And don't mention Porsches around Serious, as it will derail this entire thread.

Well said.

[arggg45]

Originally Posted by BookerM3

As for make the Z4M competitive, anything is possible with enough money,
time and effort.

Exactly. I'm working on building mine for a class that many view as "Spec C5ZO6" i.e. NASA TTA. I don't think that the effort has been taken by a Z4M owner to build a TT car to the fullest extent of the rules.

Mathematically, should it be competitive? Yes. Realistically, will it be competitive? It depends on how many hundreds or thousands of hours it is going to take to get the build exactly right, the setup exactly right, and the day the driver has.

Do I understand that I am throwing money into modifications into a car that will never recoup their value? Yes, the car is a depreciating asset. I have no intentions of ever selling it.

[Serious]

Originally Posted by johanness

Has it occurred to any of you nay-sayers that Chris is doing all of this to garner the experience and end up with an exceptionally unique and superfine ride? I'm sure the cost of doing this doesn't keep him up at night, and I'm pretty positive he couldn't give a rats-ass about re-sale or penny-pinching. If so, I'm sure he probably would have went down the stereotypical race-build of an E36 or Miata. If you still question why he's doing this and suggest these rides... then you've totally missed the point.

I say go for it. Your car is already one of the nicest around on these forums, and will continue to be the standard set for a lot of people. I'm sure what you end up with will give more than enough people a wicked run for the money, while maintaining a one-of-a-kind feel.

And don't mention Porsches around Serious, as it will derail this entire thread.

You would get just as much experience building any car. Also unless OP plans on building the bar himself what exactly is he going to learn?

Besides it's not the cost of building the car I worry about, it's the cost of putting it on its roof and being left with a $60,000 bottle opener.

[Shipkiller]

Chris,

Have you talked to this guy: http://www.rollcageguy.com/

He is the one who did that really nice setup on the MC I saw/talked to in Feb at VIR and if I remember correctly that setup is similar to what you what.