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Thread: Somebody that REALLY knows, explain this to me please.

  1. #1
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    Somebody that REALLY knows, explain this to me please.

    First off, I DON'T HAVE A DOG IN THAT HUNT! (That's Texan for: I don't have a stake in that matter one way, or the other)
    However, some interesting statements and objections have been raised over a design issue, and I would like to know THE TRUTH about the TECHNICAL matter, as it may have some fabrication implications for a future project I'm considering doing MYSELF.
    Sorry, for the caps and bold lettering, but I want to make sure it's understood I am NOT trying to revive a heated financial discussion concerning two respected members of this forum, just settle a TECHNICAL question as it pertains to MY potential application. The pictures I am using are "borrowed" from another post, where they were used for a DIFFERENT purpose and intent, but they happen to suit my needs perfectly when it comes to illustrating MY question.(so yeah, I stole them, rather than searching the internet for similar ones because it was easier :P )

    Below are 3 different front suspension setups.
    The first is OEM Ferrari design.
    The second and third are Speedlab Corvette racing suspension.
    The fourth, FOR ILLUSTRATION PURPOSES, is Murcenary's by MM.

    Background:
    I was considering doing almost the exact same thing MM did for Murc's setup on a project car that I want to put bigger rims and upgraded suspension parts on. The problem is the car came with tiny 13" rims and there is not much room under there, so I will have to do some inner fender well cutting/shaping to allow for the bigger rim. This will require leaning the strut in a little and making a bracket to secure it.

    My Question:
    What is SO wrong with Murc's setup that makes it dangerous? (I don't want to die for a stupid hobby! >)




  2. #2
    Senior Member Don's Avatar
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    Re: Somebody that REALLY knows, explain this to me please.

    jtramey;

    I wouldn't know specifically what would be dangerous about Merc's setup as I don't want to wade into that either. I do have some pics for you from the custom frame I had. I took a whack of pictures of the suspension mount points etc. and C5 suspension was used. I can email them all to you if you PM me with your address. I think I have a couple dozen different angles and the frame was very well built.

    I'll throw a couple in here to show the point but the frame had mount brackets for the control arms similar to the custom frame you show in the middle. These were adjustable by adding shims in behind the mount against the frame rail. The frame rail has tubes welded through them so that you have a very solid mounting and tightening surface to contact with. With a C5 setup, you would remove the bracket and mount the C5 bolt mounts to the strength tubes and shim as required. I would suggest you get the frame rails pretty darn close to where you want them though so you don't use too many shims to setup the proper angles.

    The shock mount is one of the more important items to ensure is strong. You will see on the frame, it is a square tube frame welded on top of the frame rail with a tube between the upper and lower frame rails for additional strength. I planned to weld some additional gussets on each side and back of the shock mounts as well to secure the shock mount that much more. With my current build, I have a coil over on the front and I added some stiffening gussets to the back of the mounting plate I welded into the frame to hold the top shock mount.

    Hope this helps.
    Don
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  3. #3
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    Re: Somebody that REALLY knows, explain this to me please.

    Any kitcar is unsafe, even mine and i actually get to xray my welds. "Father in law runs shop that builds gas tubes so its free" but still whats a safe car? i havent been in many oem cars where i felt secure. All i say is please take the time and money to weld the chassis right so the stretch doesnt snap while driving. Thats about the most you can ask for. i would say though when you mount a shock a single bracket imo would be stronger than 2 seperate ears for the shock to mount too. i believe it would be more stable and have less chance of flex and fracture.

  4. #4
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    Re: Somebody that REALLY knows, explain this to me please.

    Murci's suspension setup raises some concerns for me. Using bolts through frame with what looks like washers to space them, and it looks like they only have a one bolt per side? Maybe the picture cutting off the angle though. Upper shock mount also could deflect and cause a failure in the craptastic booger welds. Really the welds concern me the most on that setup. Never know how things really will hold up over time, stress, vibration, torsional forces on the Control arms all act constantly to want to tear suspensions apart.

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    Re: Somebody that REALLY knows, explain this to me please.

    Ill also add that even though i dont see any problem with the upper control arm i hear there may or may not be one, not my problem so i dont care. but i do want to correct the statement that the upper arm has no stress that is incorrect. true it carries no load at a stand or under downforce, but side forces are 50% of the game and 100% of circut racing EX: F1. When making a hard turn load from the lower arm/shock to pulls on the wheel and transfers load to the knuckle and upper arm "if you have traction". So there would be load in side forces. ONCE AGAIN i am not in the fight i just wanted to make that clear before people started making deadly mistakes in there build

  6. #6
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    Re: Somebody that REALLY knows, explain this to me please.

    I'm just going to make some comments and they should be taken as that comments. Not a reflection of what I think of someone elses work. It would not be fair for anyone to analyze something from a photo. The third photo is not terrible. If you are thinking about using Corvette suspension just consider keeping as it was designed. Meaning measure everything, the relationship of the arms to each other and maintaining some antidive and if you modify track width does that effect your bumpsteer. I say some anitdive because I don't know if you are dealing with a midengine car or front engine. Most say max 6 deg (although 2-4deg is common) for front engine and much less for midengine. As far as the stack of washers, well there may have been cleaner ways of doing it, but the fact is GM has been using large stacks of washers and shims on the upper control arm since the Chevelles in the 60's and right up through they quit with upper control arms in lieu of struts. I'd be more concerned with the bolt and washer grade than the fact they were spaced out with washers. I can't see from the pic how the bolt is fastened, I assume with a washer and locknut on the backside. I really can't tell from the pic but the shock mount (and all points for fact) must not deflect and fatigue.
    As far as the middle picture of the race car suspension, performance is the only rule there. That will ride like it has no suspension at all. The suspension travel is likely only a degree or two based on the orientation on the control arm ends.

  7. #7
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    Re: Somebody that REALLY knows, explain this to me please.

    Quote Originally Posted by bartman
    I'm just going to make some comments and they should be taken as that comments. Not a reflection of what I think of someone elses work. It would not be fair for anyone to analyze something from a photo. The third photo is not terrible. If you are thinking about using Corvette suspension just consider keeping as it was designed. Meaning measure everything, the relationship of the arms to each other and maintaining some antidive and if you modify track width does that effect your bumpsteer. I say some anitdive because I don't know if you are dealing with a midengine car or front engine. Most say max 6 deg (although 2-4deg is common) for front engine and much less for midengine. As far as the stack of washers, well there may have been cleaner ways of doing it, but the fact is GM has been using large stacks of washers and shims on the upper control arm since the Chevelles in the 60's and right up through they quit with upper control arms in lieu of struts. I'd be more concerned with the bolt and washer grade than the fact they were spaced out with washers. I can't see from the pic how the bolt is fastened, I assume with a washer and locknut on the backside. I really can't tell from the pic but the shock mount (and all points for fact) must not deflect and fatigue.
    As far as the middle picture of the race car suspension, performance is the only rule there. That will ride like it has no suspension at all. The suspension travel is likely only a degree or two based on the orientation on the control arm ends.
    Using the washers to me just tells me someone was either building on the cheap, wanted something done quick, or didn't have the knowledge to engineer and build the part adequately. The bolt is likely to bend over time I guarantee it no matter what grade it is, but the welds are my biggest worry, they don't look to have been done using proper shielding gas, and globbing on both sides like that leads me to believe it was done out of lack of understanding of how to weld a thinner piece of metal to a thicker one. I don't know much about the suspension setup, but I'd definately think that whole frame build needs re-engineering and professional attention to the welds.

  8. #8
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    Re: Somebody that REALLY knows, explain this to me please.

    There are so many things wrong with this build (suspension) even the crash test dummies would not try to defend it. Oh you had an engineeer sign off on this did you ??
    Go straight to the lawyer do not pass go ...

    The short answer is if you even think this was safe turn in your drivers licence and take the bus we will all be safer for it.

    Sorry dudes this really annoys me !!!


  9. #9

    Re: Somebody that REALLY knows, explain this to me please.

    Perhaps some of you should consider adapting independent suspension subframe assemblies from production cars.

    The Miata MX-5 has one so does the following: Crown Victoria police interceptor, S2000, SC400 and GS400.

  10. #10

    Re: Somebody that REALLY knows, explain this to me please.

    the problem with needing that many washers to get the upper control arm to the loaction he wants is not the best way of doing it. The frame should have been bumped out there. Basically what the washers are doing is extending the length of the bolt needed and also not givnig it support along its length. Basically a bolt this long with the only solid points holding it (where it goes though the frame) will be more likely to bend. On another not based on the head pattern of the bolts it does look like he did in fact use grade 8 hardware which is good, grade b7 or 8 should be used for suspension bit to ensure strong and long service life.

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