Challenge + NHRA Rules - DOM Tubing Specs

Hey All,

Quick, hopefully simple question.

I am trying to have my z3 (convertible) challenge car ready for the challenge this year. I know to run in the drags I'll have to have a roll bar at minimum, and I'm planning to work towards a full cage. From my reading of the NHRA rules it looks like no matter the OD size of the tubing I use, .120" wall is required. Is this correct, or can I get away with .095" DOM?

Oh Crap......do open cars have to have a roll bar to drag, even slow open cars?

I did a bunch of studying rulebooks for this issue back about 6 months ago. SCCA is weight based and NHRA doesn't seem to care much about vehicle weight. They will require different braces at different places. Something expressly prohibited by one might be required by the other. Etc.

It will be quite hard to get something that meets the exact letter of both rulesets, and if you do, it would probably weigh as much as a z3.

My advice: Figure out what you think is safe and meets either NHRA or SCCA rules. Then get it touch with GRM to see if it will be acceptable.

DeadSkunk wrote: Oh Crap......do open cars have to have a roll bar to drag, even slow open cars?

Convertibles faster than 13.49 require roll bar according to the quick reference chart: http://promod.nhra.com/userfiles/file/Tech/2017_NHRA_Rulebook_Quick%20Ref.pdf

however, I think "dune buggies", or cars with no windshields, etc are treated differently so if you fall in one of those categories you might want to look closer.

Here's the page I put my notes from my review. Note that I focused on roll bars only, not cages.

https://grassrootsmotorsports.com/forum/grm/calling-all-roll-cage-experts/127733/page2/

In reply to Robbie:

Thanks for the link. I'll be driving a full bodied (including windshield) Miata, and 13.49 won't be on the menu.

DeadSkunk wrote: In reply to Robbie: Thanks for the link. I'll be driving a full bodied (including windshield) Miata, and 13.49 won't be on the menu.

It would appear that my z3 stock would run a 4.6, supposedly. Add weight reduction is really the only performance modification here, so I'm not sure that would gain me enough time to give me an issue here, but I really have no clue how drasticly anything affects the 1/4 mile time.

I may end up just building to SCCA spec as for the most part it is going to be for drifting and autocross, and if it's not good enough to run drags in the challenge then I just won't. I kinda doubt it'll be fast enough to be an issue though.

In reply to AWSX1686:

I think the ol' rule of thumb I've heard is 100lbs=0.1s off your e/t.

Use this: http://www.wallaceracing.com/et-hp-mph.php

We use it a lot. It will get you pretty close in a car with an automatic and slicks.

Of course, if you are planning the drift/autocross the car, you may want the cage anyways.

I went through this and am still going through this, the SCCA rules are to a much higher standard across the board, for all systems. NHRA techs are sometimes a genuine joke, last time I drag raced they were most concerned with my foot wear and never even checked any of the expiration dates on the seat belts and door nets.

You won't be able to build a cage that meets NHRA and SCCA in a practice way. Rules don't jive.

The Challenge is run on an NHRA track. It's their safety rules.

(But most of us would rather build an SCCA cage than an NHRA cage)

What will your car run in the 1/8th and 1/4th mile? Under a certain Speed/Et you don't need a cage, a simple roll bar and arm restraint will do the job and be totally legal. I've seen cars without a bar/cage at all running with a hard top and I've seen cars with the wrong cage be denied at tech. Odd rule, if you run without you're just fine, when you install a bar/cage/aftermarket belts, exhaust, etc., in the very same car, you have to meet NHRA bar/cage specs. Most of the time it's better/cheaper/easier to just to run without. You have to get pretty high on the ladder to need a cage or even a bar. On a curious note, SCCA allows for the live fuel line to run right along the trans tunnel, NHRA won't hear of it ! Certain things make no sense at all on both sides, don't sacrifice obvious safety factors, you're dealing with a life here, they're most often most concerned with a single sentence on a paper page out of a rules book, make it as safe as you possibly can.

Two_Tools_In_a_Tent wrote: What will your car run in the 1/8th and 1/4th mile? Under a certain Speed/Et you don't need a cage, a simple roll bar and arm restraint will do the job and be totally legal. I've seen cars without a bar/cage at all running with a hard top and I've seen cars with the wrong cage be denied at tech. Odd rule, if you run without you're just fine, when you install a bar/cage/aftermarket belts, exhaust, etc., in the very same car, you have to meet NHRA bar/cage specs. Most of the time it's better/cheaper/easier to just to run without. You have to get pretty high on the ladder to need a cage or even a bar. On a curious note, SCCA allows for the live fuel line to run right along the trans tunnel, NHRA won't hear of it ! Certain things make no sense at all on both sides, don't sacrifice obvious safety factors, you're dealing with a life here, they're most often most concerned with a single sentence on a paper page out of a rules book, make it as safe as you possibly can.

I believe the Challenge is 1/4 mile, and that's really all the drag racing the car would ever see.

At this point I am really leaning towards building to SCCA spec and if it's not good enough for NHRA at the challenge then I just won't run drags. I'm going to the challenge to have fun, not to win. (Have to double check, but I am thinking 1.75"OD w/ .095 DOM is well within spec for my car and can easily be handled with the bender I am looking at.)

The Challenge is 1/4 mile.

There has never been a car at the Challenge that required a cage, and very few require a roll bar.

Don't overthink it.

However, that doesn't mean they have to allow you to run with a substandard roll bar or cage. If you have a cage, it needs to be built the guidelines. There is only 1 tech inspection, not separate ones for the AutoX and drags. If you fail tech, you don't run at all.

Tech has been very lax in past years, but is expected to be more careful this year.

SVreX wrote: The Challenge is 1/4 mile. There has never been a car at the Challenge that required a cage, and very few require a roll bar. Don't overthink it. However, that doesn't mean they have to allow you to run with a substandard roll bar or cage. If you have a cage, it needs to be built the guidelines. There is only 1 tech inspection, not separate ones for the AutoX and drags. If you fail tech, you don't run at all. Tech has been very lax in past years, but is expected to be more careful this year.

So perhaps I start with a roll bar that is bolt in, and if it's not to their spec, I can just take it out...

In reply to AWSX1686:

Your Z3 will not require a roll bar unless it runs 13.49 or faster according to the NHRA.

Your weight reduction will be offset by the weight you put back in the roll bar, so you won't be running 13's. Stock car ran a 14.8 when new. If you are doing no power mods at all, I'd be shocked if it breaks into the 14's (because the car isn't new anymore)

K.I.S.S.

Or, skip the roll bar and save the money for something that you'll really need. Do you know what class you'll be running in SCCA Solo? In reality, you probably only need spend money a helmet and a bolt-in kitchen extinguisher, anything else is just "boy racer" crap. ALWAYS build to the class if you're planning on having anything to do with SCCA sanctioned events.

Have you ever competed in an NHRA drag race before? From what I've seen and what the rules book reads, you're not going to need any sort of roll bar or cage at all to be legal. I don't think that you're required to have a bar until you run better than a 13 or 14 quarter mile, unless your car is modified, you're fine.

In reply to wheels777:

My apologies.

Andrew has brought a car that required a cage.

Your Z3 will not require a roll bar.

According to a specific question I asked Tom, GRM will have limited authority to allow some leeway when NHRA AND SCCA rules are in direct conflict. E.g., I've relocated my battery so a remote electrical system cutoff switch is required. SCCA only requires it to be accessible from outside car; NHRA requires it be mounted on rear most part of car behind rear wheels. My switch will be accessible through passenger window. In this situation GRM will allow me to run under SCCA rule, including drags. In an open top car you will be required to use full coverage helmet WITH eye protection.

I would think they will have same flexibity on an SCCA spec cage, especially since it's unlikely you'll be running a sub 13.49.

As SVREX stated...don't over think it...KISS.

Good to know guys. In this case I will probably just hold off on the whole roll bar/cage until after the challenge.

When it does come time to build the cage, I will mostly be building it for drifting purposes (which are usually pretty lax rules) so I'll just go to SCCA or better spec in case I want to do the occasional autocross.

What is KISS/K.I.S.S. by the way??

Keep it super simple?

AWSX1686 wrote: Keep it super simple?

Close, but it ends with "comma stupid"

Robbie wrote:

AWSX1686 wrote: Keep it super simple?

Close, but it ends with "comma stupid"

Ahhhh