Chromoly vs steel and other roll bar stuff.

[turbohunter]

Pretty soon I'll be paying my pesos to have a roll bar and the subframe connectors installed in the Fairlane.
Figured I should have a pro do it as I know my limitations.
Trying to be smart  about which material to use for the roll bar.
From what I know chromoly is stronger lighter and more expensive.
Do I need it? Will I run into certification trouble if I don't have it?
Pros and cons?
Also 6 point vs 8 point. Thinking about the future and the car getting faster and ease of add ons.
From what I remember in the rules they are pretty lax (qualified) until you get into the 9s. I'm thinking 11.0 for now.
I'll search the rulebook again but would like real world experience.
Thanks for your time.

[machoneman]

Moly now! If one does plan to go faster, going the cm route is best as one can add more bars later, if need be.  Given the correct NHRA wall thickness in the fast classes, you'll never hit the limitation(s) of mild steel. JMO as it's been years since I built a caged racer but......!

[jayb]

The chrome moly tube thickness requirement is about .083", and the normal steel tube thickness requirement is about 0.135", if memory serves.  That is a big difference in weight; I calculated that going chrome moly saved me 60 pounds on my Shelby clone.  To put a 10 point cage in my Shelby clone required about $500 of chrome moly tubing.  To go up to 10 flat you only need a 5 point cage (main hoop, two back support braces, and a side brace on the driver's side that can be removable).  You might spend an additional $150 or so going with chrome moly, with a weight savings of about 30-40 pounds over the normal DOM steel tube.

[sumfoo1]

Ok i differ from the above poster's position even though i wish i went chromo.

My opinions are this... Do an 8.50sec cage out of mild steel with removable door bars.

The reasoning is as follows... you are going beyond reason with a street car when you go beyond 8.50. 
You will have to completely re-do the cage anyway to go faster than 8.50.

Chromo over time will stress crack and mild steel won't.  That's why cage certs only last a few years, to force you to inspect for cracking.


Also what car is it going in? is it a car where 50lbs will be a big deal or not?  (are we talking 3000lbs or 3500 or 4000)

[thatdarncat]

CM by the rules has to be Tig welded ( heli-arc ), MS can be Mig welded ( wire feed ) I think the lack of a Tig welder is what keeps some people from using CM. Personally, if you're having a professional do the job I'd say go CM for the reasons Jay stated and because I'd assume they would have a Tig welder. Also know the tube wall thickness in the spec (.118 for MS) is a minimum so a thicker wall tube is used to start with since when it is bent for a curve the metal stretches and gets thinner. That is why .135 MS is used as Jay mentions. When NHRA checks it they use a sonic checker and will check the bends. A pro chassis builder would know all this. The advice I would give is ask for references to check other bars and cages a pro has done, experience gives the good ones tricks to make a cleaner installation. With all that being said I went with a MS bar in the car I'm building since I was able to talk a good friend ( and good welder ) into doing mine.

[ScotiaFE]

Recently bent a hoop for a 67 Fairlane.
Used the DOM mild steel. Not weight racing just having fun.
Not that hard to make your own hoop.
Might want to do a cost analysis.

http://fepower.net/simplemachinesforum/index.php?topic=1903.0

[sumfoo1]

http://www.nhra.com/UserFiles/file/General_Regulations.pdf

Page 22 is what i reference.

[babybolt]

There's a new roll cage material on the market now:

http://www.circletrack.com/chassistech/1402_building_a_racecar_chassis_tech/viewall.html

Whatever you get, make sure its not the Chinese crap (make sure the tubing source is traceable).

[sumfoo1]

If SFI/NHRA/IHRA/NMCA doesn't have it in the spec does it still count?

[Heo]

There's a new roll cage material on the market now:

http://www.circletrack.com/chassistech/1402_building_a_racecar_chassis_tech/viewall.html

Whatever you get, make sure its not the Chinese crap (make sure the tubing source is traceable).

The steel company SSAB that makes that steel  is in the next from where i live and Planja
hard tech that press chrash beams and so on for most of the car manufacturers in the world

[turbohunter]

NHRA says from 10.99- 10.00 you need a cage.
As far as I can tell they define a cage as 5 points and up.
Does that jive with what you guys know?

[ScotiaFE]

The Roll Bar is the 5 or 6 point setup. Which is good to 10.00.
The Roll Cage is the full monty with roof bars and A pillar bars. 9.99 or quicker.

 

[FEDER]

My Son bought all cm tubing for the 65 comet build He is doing. Enough to cert 8.50. He spent weeks pricing matl on the internet. We live in Washington State. Best price He found was in Floida. With shipping it was still cheaper to buy it there. We will bend it up ourselves but it cost near $1,700 bucks.So if a pro shop does it the matl will be marked up then install very expensive. Just for the weight savings. It's ALOT cheaper to get a cage kit from one of the big shops like Alston or whoever already bent up for your car. And you local fab Guy can install it.JMO

[bn69stang]

Have to agree with the above , chromoly is  strong - mild steel is durable .. It s your choice , decide street car or race car .. Bud

[TomP]

The Chrome Moly in my Comet came from the local steel supplier, Wilkinson. I bought it years ago when working at a fab shop.
 The .134" wall is way too heavy. I had the hoop for my Capri bent up at a local shop that used that but the braces will all be the .120" wall i'm a bit happier with. The .120" HREW will usually sonic OK but the problem is some tubes are bad batches. We saw holes in the walls of the 1" x .065" that was bought by the truckloads on maybe one tube per thousand. Perhaps three tubes per thousand would show a weak wall when you bent them. (stretched outer wall would cave down)
 Using .120" wall DOM tube would not be a problem. It's quality is consistent as is moly.