Roll bar guidance please

[profeser]

I am getting ready to build a four point roll bar for the Miata. I have looked into Kirk Racing, and Hard Dog bars. I had a hard dog hardcore hardtop in my last Miata, and liked it but want a slightly less intrusive design for this car. My question is, is there a general spec for tubing diameter and wall thickness? I read the GCR's and saw the specs for full cages, but couldn't find anything regarding just a four point bar. Just the list of "recommended" bars. Hard Dog bars are 2" and 0.120" wall DOM, and Kirk Racings are 1.75" x 0.120" wall DOM. I would like to build my new one out of either 1 5/8" X 0.120 wall 4130 cromoly or 1 3/4" x 0.120 wall 4130 cromoly. A friend has a mandrel bender with a die for the 1 5/8", will that pass safety tech or do I need to go with 1.75" minimum diameter?

 

Thanks

Paul

[brkntrxn]

I have the Boss Frog double hoop in my 2000 Miata and really like it. If you are only time trailing (vs w2w), have you thought about that version? It is legal out of the box for DE and TT with NASA and most other organizations.

[TurboShortBus]

You can't go wrong if you follow the recommendations for roll cage tubing when building your roll bar. That will let you complete the rest of the cage without starting from scratch if/when you decide to go W2W with the car instead of just HPDE and TT use. Do not use ERW tubing at this time if you might eventually go racing; get DOM tubing (about 2x the price as ERW, but less than chrome moly). Without getting into a heated discussion about metallurgy (which you can do in any one of thousands of other forums elsewhere), there is no need for CM tubing; DOM MS is fine. Based on the 1.625" die, I can tell that your friend likely builds drag race cages, so don't let him talk you into thin-wall CM if you might race the car in the future.

 

This is not an official response, but if the roll cage section of the rules calls for 1.50" x 0.120" DOM tube and you use 1.625" x 0.120" DOM tube, it seems to me that you have exceeded the requirements. I know of a car that is heavy enough to require a cage that is built from 1.75" x 0.120" DOM tube but actually has 1.875" x 0.120" DOM tube, and it has a valid NASA logbook.

 

But, since there are no dimensional requirements for HPDE/TT use, it will be hard for you to fail tech unless you really build a piece of crap.

 

Mark

[Varkwso]

You can't go wrong if you follow the recommendations for roll cage tubing when building your roll bar. That will let you complete the rest of the cage without starting from scratch if/when you decide to go W2W with the car instead of just HPDE and TT use. Do not use ERW tubing at this time if you might eventually go racing; get DOM tubing (about 2x the price as ERW, but less than chrome moly). Without getting into a heated discussion about metallurgy (which you can do in any one of thousands of other forums elsewhere), there is no need for CM tubing; DOM MS is fine. Based on the 1.625" die, I can tell that your friend likely builds drag race cages, so don't let him talk you into thin-wall CM if you might race the car in the future.

 

This is not an official response, but if the roll cage section of the rules calls for 1.50" x 0.120" DOM tube and you use 1.625" x 0.120" DOM tube, it seems to me that you have exceeded the requirements. I know of a car that is heavy enough to require a cage that is built from 1.75" x 0.120" DOM tube but actually has 1.875" x 0.120" DOM tube, and it has a valid NASA logbook.

 

But, since there are no dimensional requirements for HPDE/TT use, it will be hard for you to fail tech unless you really build a piece of crap.

 

Mark

 

 

Anything you install for TT needs to meet the general CCR requirements if your region requires logbooks/annual tech for TT.

[profeser]

You can't go wrong if you follow the recommendations for roll cage tubing when building your roll bar. That will let you complete the rest of the cage without starting from scratch if/when you decide to go W2W with the car instead of just HPDE and TT use. Do not use ERW tubing at this time if you might eventually go racing; get DOM tubing (about 2x the price as ERW, but less than chrome moly). Without getting into a heated discussion about metallurgy (which you can do in any one of thousands of other forums elsewhere), there is no need for CM tubing; DOM MS is fine. Based on the 1.625" die, I can tell that your friend likely builds drag race cages, so don't let him talk you into thin-wall CM if you might race the car in the future.

 

This is not an official response, but if the roll cage section of the rules calls for 1.50" x 0.120" DOM tube and you use 1.625" x 0.120" DOM tube, it seems to me that you have exceeded the requirements. I know of a car that is heavy enough to require a cage that is built from 1.75" x 0.120" DOM tube but actually has 1.875" x 0.120" DOM tube, and it has a valid NASA logbook.

 

But, since there are no dimensional requirements for HPDE/TT use, it will be hard for you to fail tech unless you really build a piece of crap.

 

Mark

 

Yes my friend does usually build drag cages, and I won't build a POS... I just wondered about diameter and wall thickness, since a full cage also has the front portion of the halo and down tubes to help carry the full weight of the car if things go pear shaped. Where with a 4 point bar only, thats it. Just one hoop for the full weight of the vehicle. Obviously better to over build than skimp...

 

Thanks again for the advice

Paul