MR2 roll cage

[V6SW21]

Looking at replacing my Autopower roll bar with a roll cage. I initially wanted to run rear braces from the main hoop to the rear strut towers. I was going to remove the rear windshield and replace it with 3/16" lexan. The curved portion of the stock window would be made of composite. This would allow the rear braces to pass through the window and the cabin to remain sealed. Upon reading further into the CCR, I saw 15.6.11.A Rear Braces - Exceptions.

 

15.6.11.A Rear Braces - Exceptions

On cars where the rear window/bulkhead prohibits the installation of rear braces

(Porsche 914, Pontiac Fiero, etc.) the main hoop must be attached to the body by plates

welded to the cage and bolted to the stock shoulder harness mounting location. There

must also be a diagonal bar connecting the top of the main hoop to the lower front

passenger side mounting point (“Petty bar”). Some cars built for racing in other

recognized sanctioning bodies may be granted a waiver of this rule, however they must

show proof of compliance with the current published rules for their class.

 

So the MR2 is alot like a 914 or Fiero. Can I not pass through the rear window?

 

I was also curious on the Petty bar topic. Is the petty bar allowed in all cages or just this exception? I cant recall always seeing the Petty bars in the race cars at each track day.

 

Thanks everyone.

[kbrew8991]

You can do either way - up to you and/or class rules - ie if class rules prevent you from going through the window then you'd have to use this exception only unless there's another area to brace to that isn't too extreme an angle.

 

My car (Mk2 MR2 as well) currently does not have anything cage-wise reward of the main hoop, and uses that exception to get by. That portion of the CCR does not require you to do things exactly that way (ie no rear braces, only petty-bar & extra main hoop braces on the sides) but simply gives you the option to do it that way *or* to have rearward bracing of the main hoop along the lines of a more traditional cage design like you'd see in a sedan/hatchback/etc being that it's explicity listed as an exception.

 

Also note - the cage design area in the CCRs only lists the minimum requirements to pass inspection and recieve a logbook. Class rules take over from there to define the maximum you're allowed to do. Most class rules let you brace as much as you want within the allowed 6-8 attachment points/plates/plate sizes, and some classes will even let you add as many attachment points/plates/etc as you wish. A petty bar is a good example of a common inter-point / inter-cage extra brace - not required in a traditional design, but one that some people choose to add. It would only be required if you chose to use the exception portion you list above however since it would try and replace the reward support of the main hoop typically provided for in more traditional cage designs of course.

 

Hope that helps! Oh and let me know if you would like to see any pictures of my cage design for ideas that work or ideas of what isn't so great about it. It's an Autopower kit (I believe anyway, its an ex SCCA SSB car that was mostly ready to go when I purchased it) and something more customized/fabricated would fit alot better. The halo portion on these cars is critical to get right for headroom / helmet clearance for example...

[V6SW21]

Thanks for the reply Ken. Its a TT/PT car.

 

47) Add rear strut tower bar (two attachment points—bolted in or as a component of the cage)

48) Lexan windshield, rear window, and rear passenger side windows (windshield must be 3/16”

minimum thickness). (See section 7 Safety regarding front side windows)

 

So I think I should be ok, but Ill probably still email Greg. The cage is a pretty expensive component if it doesnt meet the rules haha.

[kbrew8991]

Doesn't hurt to ask Greg at all

 

Be sure to mention that there really isn't a better way to brace the cage and mention that these few car types already have a special allowance in the CCR so it would not be unprecedented to allow this as a freebie.

[bigbird4120]

Thanks for the reply Ken. Its a TT/PT car.

 

47) Add rear strut tower bar (two attachment points—bolted in or as a component of the cage)

48) Lexan windshield, rear window, and rear passenger side windows (windshield must be 3/16”

minimum thickness). (See section 7 Safety regarding front side windows)

 

So I think I should be ok, but Ill probably still email Greg. The cage is a pretty expensive component if it doesnt meet the rules haha.

 

 

This may be moot by the time you read this, but I just saw the post.

 

My MkII NA has both rear bracing in the cockpit and bars extended to the strut towers. Needless to say, the rear window has to come out, and has been replaced with a lexan rear window. [i got mine from Peter Doane, an SCCA racer with an ITA MkII NA, who is most helpful. He has some very detailed builds for this car on MR2OC.com in the Road Racing forum.] I have received tentative approval from SE PT director Jason Plante for this car to be a PT racer to this point I can't remember if he specifically mentioned the lexan rear window/strut tower bars, but he did make cage recommendations in other areas, so I know he looked at it all.

 

If you are still building, I reccommend Peter's build thread as the best for a racing MkII I have ever seen. His handle is PDoane on MR2OC.com. You know also, that if your screen name indicates the motor you intend to race in that car, that you have to have specific National director approval of classing, dyno numbers and points assesment, right? Additionally, I have no official standing with NASA, as does KBrew, just personal experience, so take it for what it's worth, and check it out for yourself in your region.