ROLL CAGE Wednesday, 23-Aug-2000 03:04:45 Message: 205.188.197.178 writes: I need some opinions on what type of metal to use on building my roll gage. I hear differnt opinions, do I use chromoly or mild steel.For now I'm going to go with a 6pt until I can get the ghia to run in the 10's, still need to run it on the track with the turbo. How much weight differance them both.... RAY MEJIA

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Replies:

I think 4130 Chromoly will offer more protection than Hi-ten. If you do go for Mild steel make sure you use CDS. (Ant Lockyer) (23-Aug-2000 04:47:26)

If you can afford the chromoly go for it. It is both stronger and lighter than mild steel. (n/t) (iluvnos) (23-Aug-2000 08:16:59)

Re: ROLL CAGE clarification on Chromoly vs. Mild Steel (Rick M) (23-Aug-2000 08:47:03)

Re: Re: ROLL CAGE clarification on Chromoly vs. Mild Steel (Jeff N.) (23-Aug-2000 13:14:54)

I have an 8 point RLR cage sitting on the garage floor. I haven't weighed it, but it has some pretty serious mass. Lotsa tubing. It is around 100 pounds I bet, less than 150 I'm sure. (n/t) (Steve Arndt) (23-Aug-2000 13:36:19)

Re: ROLL CAGE (Tracy G) (23-Aug-2000 10:46:59)

Re:The chromoly in .083 will be about 1/3 the weight of mild steel with .118 wall thickness (NHRA min.) (n/t) (Phil) (23-Aug-2000 19:55:57)

you do mean 1/3 LIGHTER, right? (n/t) (John Connolly) (24-Aug-2000 09:52:10)

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Re: ROLL CAGE clarification on Chromoly vs. Mild Steel Wednesday, 23-Aug-2000 08:47:03 24.4.254.2 writes: Many people keep getting the impression that Chromoly is lighter than mild steel roll bars. not true! The only reason that myth got started is because chromoly is actually stronger than mild steel it allows you to use a lighter guage or thinner wall tubing. That is where the weight savings comes in. If you were to use a .120 wall Chromoly tubing vs. a .120 wall Mild Steel tubing...there would be no weight savings. The difference in weight comes from being able to use .095 Chromoly vs. .120 wall Mild steel because of the strength characteristics of Chromoly. This is factual and anyone who has constructed roll cages and chassis will tell you the same thing. Another thing to keep in mind is that Chromoly characteristics change when welded and the chassis should be annealed (heat treated) so the integrity of the chassis is sound. Chromoly is very strong but the welding along creates weak points outside the welds where it often cracks under continuous stress. Mild Steel, on the otherhand, is more forgiving and not as brittle. Many circle track racers have used Mild Steel tubing for years which when braced properly can give you just as much good protection. If you are building a roll cage...and are concerned with overall car weight..use the lighter wall chromoly. If you are just looking for safety and it is a street car...use Mild Steel. You will be just as safe and it will cost you a lot less for a little difference in weight. This comes from personal experience so just take it as food for thought. Rick M Phoenix Rick M

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Re: Re: ROLL CAGE clarification on Chromoly vs. Mild Steel Wednesday, 23-Aug-2000 13:14:54 63.71.188.232 writes: Rick, what would you say a mild steel 6pt. cage would weigh? Lets say .120? Thanks Jeff N.

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Re: ROLL CAGE Wednesday, 23-Aug-2000 10:46:59 38.38.27.156 writes: There is no weight difference between 1020 mild steel and 4130 chromoly tubing of the same diameter and wall thickness. 1020 has a tensile strength of 69,000 psi, 4130 has a tensile strength of 86,000 psi. Because of the nearly 25% difference in tensile strength between the two materials, NHRA allows you to use .083 wall thickness 4130 in place of .120 wall 1020 on the large tubes, thus making the structure about 1/3 lighter. Be aware that 4130 is 3-5 times as expensive as 1020 and requires TIG welding which will cost you more also. It is helpful, but not necessary, to normalize (also known as stress relieving) a 4130 welded component. A properly welded and cooled part should not require this under normal circumstances. Annealing is heat treatment to soften metal and make it easier to shape and machine - this is a different process. I agree with Rick M., if this is a street/strip car have it made from mild steel, the weight difference of chromoly would probably not be worth the additional cost. Tracy G