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Im having my mild steel cage taken out and replaced with a moly one. Does a moly cage go brittle after 4, or 5 years? Where a mild steel cage can last up to 15 years? If this is the case, ill just save my money. The weight difference cant be that much anyway. Im not sure if i should stick with what i got, or replace it.

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No, a moly chassis does NOT turn brittle in 4 or 5 years
that BS. The weight isnt all that much lighter but
it is lighter, I dont have the numbers in front of
me what the difference is in a foot. Its up to you
weather you replace it or not, they do cost more
because its all tig welded, but a moly chassis is
more rigid

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I'd do a moly cage. It will last forever, it's worth more if you sold the car. You can put the weight you save somewhere else, or just save the weight.

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I also agree with MRPBODY, the moly cage is stronger, safer, lighter and better in a crash, especially on a drag car. That being said NASCAR wants mild steel, probally because a lot of the good old boys do a lot of the work themselves in the lower, slower local race cars and they don't want them trying to weld chrome moly with a OX Acetelene torch

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I also agree with MRPBODY, the moly cage is stronger, safer, lighter and better in a crash, especially on a drag car. That being said NASCAR wants mild steel, probally because a lot of the good old boys do a lot of the work themselves in the lower, slower local race cars and they don't want them trying to weld chrome moly with a OX Acetelene torch

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I believe they use mild due to them busting up their
cars all the time and always replacing tubing and
they have a PILE more tubing in their cars plus
they have a pretty high minimum weight

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Has to do with the tube absorbing shock loads. Moly being more rigid, transfers more load to the driver than mild steel.

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moly is more brittle, so wouldn' it be more prone to cracking or is that just a myth.

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Why is it more brittle Its stronger with less flex

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While it is true mild steel has a little 'give' to it, these top 2 examples of 10 second 'mild steel' cages gave way too much..... the top one was coming in on the driver and had already failed......

the second pic of a buddy of mines cage also was 'giving' and was a hairs breath away of crushing him when he got into a little (very little) antifreeze of another car that had just run.

It may be hard to see in these pics unless you can zoom in, but both these mild steel cages deflected WAY too much for safety.






This next moly caged car hit and went over the wall at Orlando and disentegrated, but the moly cage did not deflect at all and integrity of chassis was still 100% intact.

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A picture is woorth a 1000 words, these three speak volume of why all the Pro cars use chrome moly tubing in there cars. Weight and speed have a lot to do on the total impact loads, I would rather be a in a car(and I am) with a chrome moly bar or cage than mild steel any day that I'm in a crash

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While it is true mild steel has a little 'give' to it, these top 2 examples of 10 second 'mild steel' cages gave way too much..... the top one was coming in on the driver and had already failed......

the second pic of a buddy of mines cage also was 'giving' and was a hairs breath away of crushing him when he got into a little (very little) antifreeze of another car that had just run.

It may be hard to see in these pics unless you can zoom in, but both these mild steel cages deflected WAY too much for safety.






This next moly caged car hit and went over the wall at Orlando and disentegrated, but the moly cage did not deflect at all and integrity of chassis was still 100% intact.

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My mild steel cage is only legal for 10.0.

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Is this something new

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And still this question is raised.

No, moly is not more rigid than mild steel. The elasticity of all steel alloys is almost identical (Young's modulus: 30 × 10^6 psi).

"I have always heard that moly is twice as light, and twice as strong."
No, moly is not lighter than mild steel, the weight difference is only 1-2% depending on the exact alloy. The reason it's lighter is smaller wall thickness - that's it.
No, moly is not twice as strong, it's about 30% stronger (not stiffer), and that's if properly welded and heat-treated. If the wall thickness is reduced to save weight the strenghs are about equal. You can have more strength with the same weight, the same strength with less weight, or some intermediate.

Re: "they don't want them trying to weld chrome moly with a OX Acetelene torch"
Guess how Reynolds 531 chrome-moly chassis (including Formula 1 back in the day) are built for road racing? That's right - gas brazed with a torch. Read Carroll Smith.

"both these mild steel cages deflected WAY too much for safety"
That's not what did it.

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And why do you say its not stiffer, it takes a significantly
greater force to bend it on a bender over the
mild steel?

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From your first picture it is a prime example of improper installation.The piller bar is layed back way too far and is attached at the side of the halow bar.It should be attached at the underside of the halow to give any support.Many times an installer will try and follow the windshield and body contours which make the angles less effective for support.NASCAR uses MS cages for impact absorption(give)CM is lighter and harder and has little impact absorption quality.CM is more prone to break rather than bend.And because of it's hardness it will fatigue from twisting and loading in time.This is why prostock,top fuel and other classes constantly update their chassis.If you have ever seen a CM Chassis wrecked you will commonly see tubing breaking not at the welds but in the tube body.And also a good oxy/ecty welder can weld CM just as good as a good tig welder.A furthur note,with all the approved and new welding techniques CM can be mig welded to perfection,NHRA just doesn't allow it.They fear that that fitment would be compromised buy the ease of application of mig welding,where as you can't very well hide gaps with the tig process.Structural design, effectivness,fitment,weld and application are all important part of how you choose material and build a cage or chassis.

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BG and polyspheric
Great job in properly explaining the "CM/MS Myth's"

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You brought up DOM tubing, problem is, 90% of people who use MS don't use DOM, they use cheap, welded seam MS. A well built DOM cage is as strong as anything else and DOM costs nearly the same as Moly. I personally used DOM on all my MS cages, but when I got to the point that I no longer MIG welded any cage, regardless of material, it made no sense to not use Moly. Makes the car lighter and worth more for resale. I don't care what the cert is, a Moly car will always bring more. I would not put MS in a new car period, but that's just me.

Monte

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The cost of DOM(drawn on a mandral)MS to Aircraft quality CM is 1&1/2 times cheaper,we buy direct.Rolled and seamed MS is the cheapest tubing available.There are many different quality specs for either,varying the cost.We use DOM-MS and AC-CM for our custom chassis and cage work.We don't push our customer either way,we educate them on the pros and cons for their particular application and cost budget.We let them decide.Our 68 Cuda dbl rail/strut chassis car and our 65 Dodge a-arm car are both MS.We have 5 cars in the shop for up-grades,of the 5 three are MS and 2 are CM.4 of them are certified to 7.50.Go figure?

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RADICALLY different cage designs as far as I am concerned, and the material has less to do with these " crash effect" differences than the structural layout.

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I don't push customers one way or the other either....but...as I stated, I TIG everything, MS or Moly. Here in this area, DOM is NOT that much cheaper than Moly, so, if you are only looking at a couple hundred dollars more for a Moly vs MS, what would you do Bob. You also have to consider my customer base. I do very little bracket type stuff and 25.5 is about the least spec we ever build. I also still maintain that Moly cars are worth more at resale and more desirable to potential buyers.

Monte

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I'am not dis-agreeing with you Monte.I'am just stating facts from my perspective.The majority of our work is bracket cars.You deal with a limited market like you stated,25.5 spec and up.I try to relate to the majority of people on the site.I think you agree that most adverage racers here,including me are not in your league.My comments and advice is for us regular kinda of racers.Sorry if you think I was stepping on your toes.I not worthy of that.

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RADICALLY different cage designs as far as I am concerned, and the material has less to do with these " crash effect" differences than the structural layout.

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And most good design practices try to avoid "bending" in the first place, striving for just simple tension and compression forces thru triangulation, which negates much of the wall thickness advantages mentioned before. And most of these discussions usually result in those who are striving for crash protection, and the other camp striving for the most efficient and stiffess design, with the least material and lightest solution. Never ends.

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I don't push customers one way or the other either....but...as I stated, I TIG everything, MS or Moly.

Monte

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I don't push customers one way or the other either....but...as I stated, I TIG everything, MS or Moly.

Monte

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Im curious as to why M/S cages are TIG'ed. The test of a weld is that when you try to pull it apart, the material around it fails before the weld. Since a MIG weld has a larger radius than a TIG you end up with a larger surface area and (theoretically) a stronger weld. Is it for looks? A good TIG weld is usually nicer looking, but it is usually easier to get a MIG gun into the cramped areas, and you don't have to deal with trying to operate the pedal with your knee, etc. Keep in mind, I am asking this as an honest question; I know that you are a very competent builder and am not trying to insult you.

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A few of us here at BGR can make just as nice a weld with a mig as they can with a tig.It's just a little bigger weld.MS cages are usually .135 thick so when you weld two pieces of .135 material you want at least .270+- of weld width and at least the same weld thickness of the the material .135+- at the crown.These specs are from the Steamfitters weld testing for power plants and pressure vessels. But then what in hell do I know,I was only certified in only 5 states for bridge and structural and heavy equipment modification and repair.I was a student of the late Art Livinston one of the best in the business.I didn't take the test for nucular power plants.

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I don't push customers one way or the other either....but...as I stated, I TIG everything, MS or Moly.

Monte

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Im curious as to why M/S cages are TIG'ed. The test of a weld is that when you try to pull it apart, the material around it fails before the weld. Since a MIG weld has a larger radius than a TIG you end up with a larger surface area and (theoretically) a stronger weld. Is it for looks? A good TIG weld is usually nicer looking, but it is usually easier to get a MIG gun into the cramped areas, and you don't have to deal with trying to operate the pedal with your knee, etc. Keep in mind, I am asking this as an honest question; I know that you are a very competent builder and am not trying to insult you.

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A few of us here at BGR can make just as nice a weld with a mig as they can with a tig.It's just a little bigger weld.MS cages are usually .135 thick so when you weld two pieces of .135 material you want at least .270+- of weld width and at least the same weld thickness of the the material .135+- at the crown.These specs are from the Steamfitters weld testing for power plants and pressure vessels. But then what in hell do I know,I was only certified in only 5 states for bridge and structural and heavy equipment modification and repair.I was a student of the late Art Livinston one of the best in the business.I didn't take the test for nucular power plants.

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Nice resume, but IMO you didn't answer his question.

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The question wasn't directed at BGR - it was initially asked of Monty - he stated that he TIGs all cages, and I was politely asking why the preference of TIG over MIG. If it's for appearance, OK. If it's structural, how?

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Looking at that cage, a gusset to the windscreen bar and Door bar could have minimised that. It certainly does look worrying though. I can also see why certain builders use a straight bar from the door bar footing to where the windscreen bar joins the door bar.
AL....

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Alan

Anyway you can post a pic of the gusset you are speaking about for this fix?

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I don't push customers one way or the other either....but...as I stated, I TIG everything, MS or Moly.

Monte

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Im curious as to why M/S cages are TIG'ed. The test of a weld is that when you try to pull it apart, the material around it fails before the weld. Since a MIG weld has a larger radius than a TIG you end up with a larger surface area and (theoretically) a stronger weld. Is it for looks? A good TIG weld is usually nicer looking, but it is usually easier to get a MIG gun into the cramped areas, and you don't have to deal with trying to operate the pedal with your knee,

Nice resume, but IMO you didn't answer his question.

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Thanks for the compliment on the resume.For that tight cage work set you TIG up with a small torch head and a thumb control.We hardly ever have to remove headliners on cars with full interior.Foot pedals are ok for bench work.