tubing size for a-arms?
 

ok I need to order tubing for my a-arms by the end of the week. I am getting some 4130 chrome moly tubing from wicksaircraft.com (local place) but I need to select a tubing size still. the arms are about 16" long with an air bag mounted on them. would some 1.25"x .090" tubing be too overkill? this is on a daily driver so pothole durability ranks higher then weight savings right now....but I won't want to TOTALLY overbuild the setup. I was even thinking of something as large as 1.375"x.090" tubing.

You're likely to not get an answer to your question because you're asking someone to engineer a load bearing weldment that will be subjected to some nasty vibration and shock loads, as well as having a probable finite cycle life. If someone did suggest a tube size, they have no control over (no offense meant here) the quality of the welds nor the overall design.

If it failed, no matter the failure mode, the person that gave you advice could, in reality, be held partially at fault for the failure and any resulting property damage or even loss of life. As a matter of fact, I would urge anyone to avoid answering this question, or questions like it unless they have the proper insurance coverage for the situation.

Sorry dude...blame the lawyers.

ok maybe then as a better question....

what tubing sizes are used on commerically available arms?

PS...sorry $1 stag beer night nextdoor

Jim Meyer Racing has built the last 2 chassis' for me. On his design he used 1" upper & 1.25 lower. But he used mild steel DOM rather than chromoly. I have been told not to use chromoly on the street for building chasiss for a few reasons, but not sure on control arms. This is a little out of my league as to the true reasons not to. That's why I leave it to the people that know when it comes down to stuff like this! :D

could anyone else chimein on this? I could se the CM not being used since it is stiffer and would be a rougher ride than the mild. Part of the thing is that I am graduating with my under grad in mechanical engineering but none of the professors around here know anything about this kind of a situation. I have the knowledge to do the FEA on it but just don't know what kind of loading I am loking at IE is a 10,000 lb force along the cars axis enough to simulate a pothole pushing the wheel back? what about vertical forces?

Air Ride tech control arms are 1in DOM

well what wall thickness? I was looking at going to a larger diameter tube with a thinner wall maybe.....but the wall thickness is the most important part

just looked in the book .219 wall thickness

so what is the problem with 4130 tubing? just by changing to that I could cut the wall thickness in half.

I don't know that there is a problem with chrome moly...maybe companies don't use it because it is more expensive! :_paranoid

Most guys I've talked to don't use 4130N for weldments because they're scared of welding it. Seriously. It's prone to hot cracking and brittle welds, so they just don't bother. Given the prices of steels now days, 4130N isn't that much more expensive than DOM is.

And.... 1 x .219" wall???? Damn.

Ya I know I looked in the book and on the website to make sure but thats what it says...... :eek:

thats why I as looking at LARGE diameter tubing 1.375" since it will handle the bending forces better but have room to go high as 1.5" (I just feel this will be getting TOO big) well using the 1"x.219" tubing as a guide I can run FEA on those then base my tubing size on the strength comparison.

The only advantage to using chromoly over DOM is weight savings due to strength to weight ratio. If weight is not the issue stick with DOM. I use chromoly all the time repairing vintage aircraft but I gas weld it only.

Mike

well I only have access to both a TIG and Gas torch. I heard you just shouldn't MIG weld the 4130?

correct the mig welding process makes the 4130 brittle and is more proned to cracking.......

so would the 4130 be fine on a street car if welded with a TIG or Flame torch? bacily I am looking to drop some weight if I can (less unsprung mass to worry about)

btw I rehased the geomtry today (had too much kingpin at 14* and reworked it down to 9* which is making everything work much nicer!!) I have much nicer camber curve now and just tweaking in a little more ackerman (before was nearly none)

If properly tig welded yes it should be fine....

Tig will also crack as well, just not as prone. Don't ask me how I know. "If it was me", I would PRE-HEAT entire cluster with a rose bud, TIG weld, and POST-HEAT entire cluster to normalize the weld. Pre and post heating will emliminate the stress risers next to the welds that cause the cracking.

Mike

moly tubing
 

Hey guy
You don't want to use 4130 on the street thin wall or heavy wall .4130 will not last very long on the street because memory compare to mild steel .take a one foot peice and bent it and will not bend back to a netural state many time before failure. compared to mile steel DOM have a good memory that is why NASCAR used it in all their rollcage. because went one those 3800lb car flip over and over the cage is still in one piece bend but not broken (DOM mild steel).A NHRA top fuel car crash the chassis will some time break in half because it weight 1900lb (4130 chromemoly) they are looking for lite-weight.you take 11/2x.085x12 long(4130)has more strengh that 11/2x.125x12 long but the 4130 is lighter but it will work harded and break.Indy car will only use 4130 on chassis parts only and small prop air planes. I hope this help you

kendall

moly tubing
 

Hey guy
You don't want to use 4130 on the street thin wall or heavy wall .4130 will not last very long on the street because memory compare to mild steel .take a one foot peice and bent it and will not bend back to a netural state many time before failure. compared to mile steel DOM have a good memory that is why NASCAR used it in all their rollcage. because went one those 3800lb car flip over and over the cage is still in one piece bend but not broken (DOM mild steel).A NHRA top fuel car crash the chassis will some time break in half because it weight 1900lb (4130 chromemoly) they are looking for lite-weight.you take 11/2x.085x12 long(4130)has more strengh that 11/2x.125x12 long but the 4130 is lighter but it will work harded and break.Indy car will only use 4130 on chassis parts only and small prop air planes. you also have to TIG weld 4130 I hope this help you

kendall

Kendall, how about some hard facts rather than analogies. First off if either part is bending in a suspension system, it needs to be replaced regardless of what material it was manufactured with. "Memory" in which you are referring to is "how many times can the piece of material be bent with out fatigue cracking". If your a-arm is bending under load, you built it wrong and do not need to be messing with critical systems such as suspensions. The reason NHRA top fuel cars use chromoly and NASCAR doesn't is NASCAR has a minimum weight requirement and teams are usually adding weight to meet weight. If NASCAR teams could run lighter chassis, trust me, they would take full advantage of it. The breakage of a top fuel car cage due to chromoly memory is crap. At 300 mph, DOM will fail too. That is twice the speed of NASCAR, which means about 4 times the impact forces. As stated before, the use of chromoly in a suspension system, roll cage, or any other system or structure is its superior strength to weight over DOM tubing.

DOM tubing is easy to weld and can be welded by MIG, TIG, arc, or gas welded giving good quality welds without any special attention to the welded area. 4130 is not so easy. 4130 tubing is predomitely used in the "N" condition or normalized (untempered). 4130 gas welds easily, but few do it any more. On thicker tubing, usually 1/8" or thicker wall, I prefer to TIG weld. When TIG welding 4130, due to the extreme temperature of a TIG weld, 4130 will harden or heat treat at the weld but the rest of the tube will not. This sets up a stress point at which if given enough force it will crack and fail right next to the weld. Therefore when TIG welding 4130, it is best to use a rosebud torch and PREHEAT the entire area plus a few inches. After TIG welding, POST HEAT the are again plus a few inches to relieve the weld stresses and allowed to air cool. This will bring the entire welded area back to a normalized condition.

Oh....and I work on them small airplanes everyday.

Mike

I've heard most tubular arms like Global West are made from 1.250" X .125 DOM tube. If the arm is made of bent tube, the DOM is easier to make good quality bends in than 4130, this is just what I have heard, I have no first hand experience with doing it but I have bent 4130 sheet into a tri-angular tube and welded it into an A arm and it was very tough to bend.
I've seen Alston A arms for a Nova that were 1" dia mig welded, don't know the material though.