This will probably get ignored again based on purely anecdotal evidence that chromoly motorcycle frames don't break but here it is anyway. Lets try some science this time The TTT diagram below is for VCMO125 steel but that's close enough to 4130 for our purposes.

See that horizontal Ms/M line over on the left of the diagram...that is referring to Martensite structure which is to use a metallurgical term BRITTLE. This diagram clearly shows that cooling from ~850C to below ~400C in less than 10 seconds will get you pure Martensite. Guess what's going on at the edge of your MIG or TIG weld on 4130 tube as the mass of the tube heat sinks. Yep, you guessed it, Martensitic structure. The only thing saving your ignorant welding technique from more regular failures is the carbon dilution caused by using mushy 0.7% filler metal on a base material that had 3% carbon.

Now back to the regularly scheduled banter...

Dang that pesky Martensite!

This is what I was trying to say but you did a better job of it.

ignorant welding technique is ignorant.

Quote
Jon Burke
ignorant welding technique is ignorant.

Yeah those people making bike frames must not have read any books on the subject. Its a wonder that they could go and win all those World Championship Titles being such ignorant fools, isn't it?

Thank gawd we have the Intra-net and we're all experts now.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

John, you continue to miss the point by a mile. What is the base material, thickness of the material, what filler metal, and what weld process? Your broad assertions that because a motorcycle frame 20 years ago didn't break you can extrapolate that experience to roll cage tubing is ridiculous. I just showed you for like the fifth time why it's a bad idea. Prove the metallurgy works or put the shovel down and stop digging.

Quote
Tim Taylor
John, you continue to miss the point by a mile. What is the base material, thickness of the material, what filler metal, and what weld process? Your broad assertions that because a motorcycle frame 20 years ago didn't break you can extrapolate that experience to roll cage tubing is ridiculous. I just showed you for like the fifth time why it's a bad idea. Prove the metallurgy works or put the shovel down and stop digging.

Not arguing what you are saying.
I am merely voicing dismay at a) Chrome Moly as being described as "brittle" and b) that without normalizing instant end of civilisation as we know it will occur.
The failures seen in Homologated cages is very likely simply somebody choosing the thinnest possible wall they can get away with, and for a club guy, that is stupid. But that's not relevant here.

And Tim it should be evident that there is a difference in describing what has been done, and done successfully, and advocacy. I would think you'd understand that. Others no, you yes.

Things can be true--as you and the nice chart you found clearly show. (I found one showing same curves but it was French and I didn't post it cause I thought that would be rejected).
So yeah TRUE, but how significant?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Can be pretty significant. There is a large difference between a light motorcycle frame running on suspension and a 3000lb car/roll cage slamming a tree. I've welded plenty of bike frames over the years so I know they crack.

I have a friend with a front engine vintage rail dragster. A real museum quality restoration. He has a big air bladder mounted in the floor of his trailer because the frames can break while towing.

Seems like CroMo can be tigged, if careful, with the proper materials, in the proper fashion and it will work. However it seems very easy to mess up the process and have a brittle area. I have pics of a harness bar that cracked about 1/2 thru from a head-on. Homologated and just too thin for the load.

Really good news is 'we' don't allow CroMo in cages so no worries!!

I look at CroMo like this: if no one has it, it doesn't affect the RACING. Ok, so folks are missing out on a cage that's what, 10 20 40 pounds lighter? And there's no huge cost advantage by switching to it? And it's trickier to weld?

With all those, life seems simpler without it and it doesn't fix any big problems. That moves it down to priority 73 on the "let's think about this" list. (Although I'll admit I dislike that very reason for not doing something.)

Cheers,
Anders

---

Grassroots rally. It's what I think about.

Quote
john vanlandingham
So yeah TRUE, but how significant?

John, failures are more common than you think. Just because you dont see it, it doesnt mean they dont happen. Go to any small town usa with short track racing, at any given weekend you'll see suspension parts breaking off because those boys just didnt read the whole article in the Circle Track mag where it said that CroMo was good'er.

Hey you're pretty sharp for a gurl..

Seriously, you have a fantastic grasp of what needs to be done. I wish all our noobs were as sharp. You'll be just fine with the cage I'm thinking.[/quote]


we're gonna get along jjjusst fine sir!
another question for the scrutineer-man... all the rule diagram show the main roll bar as having only two bends (at the roof on each side of B-pillars) my very important question need answered so I can determine the exact positioning of my cage feet(boxes) for main hoop is :
am I supposed to add a bend where the Quarterglass begins inward and up toward the roof bend giving me a total of 4 bends in the roll cage. I know this is silly sounding because otherwise the door bars would bave to curve around the back of the seat to attach, but ALL the FIA/R-A diagrams show the roll bar as having only two boring ole ~90 degree bends at roof.

and I would have included a photo of my first prototype- of the roll bar base / box but my camera phone imploded last nite when I snapped a pic of it (it is pretty cool tho) plasma cut and then 0.035-hotwire tacked together 1/8"

Lina,

Yes you can add a bend to follow the main hoop along the B pillar.

FYI- I had my 6'6" shop manager sit in the 2002 that we were talking about. He had just enough space between the seat and the harness bar. The bar is in the plane of the short wall behind the seats. This means that any normal size person will fit in the car with the main hoop right above that wall.

---

Robert.

"You are way too normal to be on Rally Anarchy." Eddie Fiorelli.

It's not in the pics, but in the description:

The vertical part of the main rollbar must be as close as possible to
the interior contour of the bodyshell and must have only one bend
with its lower vertical part.

Yes, the top will have a less than 90, with a bend an the bottom of the glass to make the leg vertical.

Quote
Littlelina
Hey you're pretty sharp for a gurl..

Seriously, you have a fantastic grasp of what needs to be done. I wish all our noobs were as sharp. You'll be just fine with the cage I'm thinking.

we're gonna get along jjjusst fine sir!
another question for the scrutineer-man... all the rule diagram show the main roll bar as having only two bends (at the roof on each side of B-pillars) my very important question need answered so I can determine the exact positioning of my cage feet(boxes) for main hoop is :
am I supposed to add a bend where the Quarterglass begins inward and up toward the roof bend giving me a total of 4 bends in the roll cage. I know this is silly sounding because otherwise the door bars would bave to curve around the back of the seat to attach, but ALL the FIA/R-A diagrams show the roll bar as having only two boring ole ~90 degree bends at roof.[/quote]