Thread: i have a odd question

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  1. #26 Re: i have a odd question 
    Member dyn0mitemat's Avatar
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    Quote Originally Posted by JohnBoulderCO View Post
    Why? You quickly get diminishing returns on strength as the wall thickness increases and then you are just adding weight.

    Because I have an extreme abundance of it in the shop.

    I ended up deciding on 2.5"x2.5" 1/4" wall tubing though, strength shouldn't be a problem with it, nor weight (compared to solid) and I also have access to it
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  2. #27 Re: i have a odd question 
    Senior Member zjeepin's Avatar
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    Quote Originally Posted by Kraqa View Post
    I would not run 2.5 x2.5 links IMO they are probably the most ghetto links you can get. 2x2x.25 links are cheep and don’t look that bad.
    when somebody else starts paying for my parts i'll run some blingin aluminum or ht4130 but something that holds up as well as 2.5" square is tough to call ghetto IMO
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  3. #28 Re: i have a odd question 
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    Quote Originally Posted by SirFuego View Post
    Basically, yes. Also take note how quickly the MOI increases as you increase diameter/height as well.

    That said, this comparison I did is only valid for the same material. Once you start comparing different materials (such as comparing strength/weight of chromoly vs "normal" steel vs aluminum), you need to take other parameters into account for comparison since the strength and density of the material plays a role in overall strength and weight.

    I also must say that those numbers are there purely for comparison purposes to illustrate how wall thickness can at some point be compensated for by diameter and/or shape without using as much weight. In reality there may not be "much" difference between an MOI of 0.8 and 0.9 for the forces the lower control arms will see (for example), so there isn't much sense getting caught up in targeting a specific number. The trends shown by the graph are much more important than the actual numbers. I would just use 2x2x1/4 as a baseline for comparison purposes and work from there.


    another thing, hypothetically, if the square got hit from the corner, wouldnt the steel theroretically collapse? or am i reading too deep?

    and also what would be better, hot or cold rolled? i really dont know the diffrence in speaking with metal terms. yeah i know 4340 chromo is the blingy of steel, and 7075-t6 being aluminum, but what would be the better type in DOM?
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  4. #29 Re: i have a odd question 
    Senior Member dp96zj's Avatar
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    Speaking strictly from a materials standpoint, I would go with cold rolled. Cold rolled has a higher hardness, slightly higher modulus of elasticity, as well as higher tensile and yield strengths. The downside is that it has less ductility (formability), because the cold-rolling process increases the amount of martensite in the material. This makes it slightly more brittle, in turn meaning that it has lower impact strength.

    Hot rolled has a much higher ductility, but lower tensile and yield strengths, and is nowhere near as hard. Because of this, I would go with the cold rolled. Cold rolled is usually beneficial in structural applications, like cages, links, and non-wheeling related structural parts (I-beams). Hot rolled is usually reserved for when ductility and formability are needed. Hot rolled is also slightly easier to weld, but that can be corrected with proper pre- and post heating.

    Normalized 4340 chromoly will have a much higher stiffness, tensile strength (more than 2x higher than 7075), yield strength (almost 2x higher), and hardness (HRB-100 compared to HRB-87 for the 7075). Aluminum does serve its purpose for links though, since it is roughly 1/3 the weight of steel, making it a smart choice for people who are serious about shedding weight on the vehicle.

    In your case, I don't see a reason to waste money on chromo's or aluminum. Go with a plain carbon steel like most of the home-made or manufactured long-arms use and you'll be fine.
    Last edited by dp96zj; 12-01-2011 at 08:38 PM.

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  5. #30 Re: i have a odd question 
    Senior Member ATL ZJ's Avatar
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    Quote Originally Posted by zjeepin View Post
    when somebody else starts paying for my parts i'll run some blingin aluminum or ht4130 but something that holds up as well as 2.5" square is tough to call ghetto IMO
    x2. it's hard to argue against what works just because that's what pirate says your links should look like.

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  6. #31 Re: i have a odd question 
    Senior Member ATL ZJ's Avatar
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    Quote Originally Posted by cowboy63b View Post
    another thing, hypothetically, if the square got hit from the corner, wouldnt the steel theroretically collapse? or am i reading too deep?
    Not unless you hit the entire length of that corner. I have bashed a couple of mine right on the corner and it scratches and dents ever so slightly but it definitely does not fold. Smaller diameter might be a different story.

    Quote Originally Posted by cowboy63b View Post
    and also what would be better, hot or cold rolled? i really dont know the diffrence in speaking with metal terms. yeah i know 4340 chromo is the blingy of steel, and 7075-t6 being aluminum, but what would be the better type in DOM?
    DOM is the process not the material.
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  7. #32 Re: i have a odd question 
    My avatar isn't animated Lifetime Supporter SirFuego's Avatar
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    Quote Originally Posted by zjeepin View Post
    something that holds up as well as 2.5" square is tough to call ghetto IMO
    2x2x1/4 is about 5.41lb/fit.
    2.5x2.5x1/4 is about 7.11 lb/ft
    2" 0.375 DOM is about 6.51/ft.

    So assuming we are talking about 6 feet of tubing for the control arms, you are only talking 3.6lbs or 10lbs difference depending which size/shape we are comparing it to. Not a huge deal unless you want to design it such that every pound counts, but seems like it would be well worth the tradeoff in weight for a trail rig built to be bombproof. I think most people wouldn't care about the "looks" of their control arms.

    Quote Originally Posted by cowboy63b View Post
    another thing, hypothetically, if the square got hit from the corner, wouldnt the steel theroretically collapse? or am i reading too deep?
    Running all of the calculations with the square tubing rotated at 45 degrees (which would simulate the type of hit you are describing) yields the same numbers as if it was oriented "flat". Although IIRC, square tubing loses some strength if it's rotated somewhere between 0 and 45 degrees. I don't remember the calculations off hand to give you an idea of how much. Although from what I've seen, the "flat" orientation is a good estimate of their overall strength in a control arm application since most of the hits they see are primarily going to be oriented up/down instead of at an angle.

    One other thing to consider is that if you need to bend your control arms for some reason, working with round tube will be easier, but you may need to sacrifice wall thickness depending on how thick of tubing your bender can use.
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  8. #33 Re: i have a odd question 
    Senior Member ATL ZJ's Avatar
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    OK my last post for now. Can't you see I'm just padding my post count? These are key points that might give clarity to all the nitty gritty overtechnical shit posted above.

    This applies to DOM/steel links of comparable material:
    Round is stronger by weight
    Square is stronger by diameter (uneven loading/corner impact excluded)
    Increases in diameter increase MOI/strength much more significantly than increases in wall thickness
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  9. #34 Re: i have a odd question 
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    Quote Originally Posted by ATL ZJ View Post
    x2. it's hard to argue against what works just because that's what pirate says your links should look like.

    white gloves and grey poupon for kris
    i just prefer the look of 2" square. over 2.5" due to size.

    and as far as performance.....round trumps square in my books. Keep in mind that it has been a long time but i did run several square links and i bent every single one of them. seriouse abuse but they bent.

    i have yet to bend a round link more then a few degree's.

    i know that the aluminum ones are getting bent all the time. but you never really hear about that on the forums since aluminum is the new bling.
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  10. #35 Re: i have a odd question 
    Senior Member Lifetime Supporter ZJ TINS's Avatar
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    Also the weight is less for same material for square or rectanguler tube vs round tube of somewhat larger size but less capability. So round is used for cost of manufacturing not strength. Uppers can be round and smaller since they do not take a hit. But lowers should be square or rectangular (tall side vertical) if you are planning on hitting them.
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