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Push rod suspension/ Anybody help me out?

Discussion in 'The Hokey Ass Message Board' started by JPMACHADO, Nov 26, 2006.

  1. JPMACHADO
    Joined: Feb 9, 2006
    Posts: 983

    JPMACHADO
    Member
    from Not Listed

    Right now I'm finishing up my first scratch built car that has a pretty simple straight forward design. 4 bar front and back and so forth. However, when I started this first car I knew it's main purpose was to teach me what I was and was not doing right and wrong. My next build is at least 2 years away, but if this first build had taught me anything it's that you need to plan, plan, plan, and plan some more. the next car I want to be a roadster . but I want independent front suspension that has no coil overs showing. Had I spent more time planning on this first build I'd have been done 6 months ago.
     
  2. Flexicoker
    Joined: Apr 17, 2004
    Posts: 1,416

    Flexicoker
    Member

    Like ElPolacko said, we really need to know what the car is for, as that is going to dictate the suspension geometry. Carroll Smith wrote Engineer to Win. I haven't read it, but have heard good things. You're opening a pretty humongous bag of worms here. So I suggest you do ALOT of research on the matter. You don't want parallel A-arms. As your car rolls into a corner, you're wheels are going to lean outwards. You want the opposite to happens. So on most cars the upper a-arm is angled down towards the car. You also need to worry about caster, trail, scrub, ackerman, bumpsteer, etc. Do you know what uprights you're going to use? Also, the longer your A-arms are, the less track width change you'll incur during suspension travel.

    If you'd like, I can help you crunch some numbers with this, and help you figure out placement of your bellcranks and mounts and such, but I need some basic dimensions and 'windows' as to where you need to put things.

    Here's some pictures of cars I've helped build, and a link yo a formula SAE competition that has all kinds of suspension configuration... notice the angle of our upper a-arms. I used links because some of them are pretty huge.


    http://img.photobucket.com/albums/v237/Flexicoker/Formula%20SAE/IMG_5012.jpg

    http://img.photobucket.com/albums/v237/Flexicoker/Formula%20SAE/IMG_5011.jpg

    http://img.photobucket.com/albums/v237/Flexicoker/Formula%20SAE/IMG_4998.jpg

    http://img.photobucket.com/albums/v237/Flexicoker/F06/FSAEWest6-14-2006Alex039.jpg

    http://img.photobucket.com/albums/v237/Flexicoker/F06/FSAEWest6-14-2006Alex038.jpg


    http://smg.photobucket.com/albums/v237/Flexicoker/FSAE%20Competition%2005/

    Hope that helps
     
  3. JPMACHADO
    Joined: Feb 9, 2006
    Posts: 983

    JPMACHADO
    Member
    from Not Listed

    I actually have Engineering to Win, but have only read in it as I needed to. I would love to keep your post and write you back when I'm far enough into the design stage to have actual numbers. If this is okay please PM me so I have a record of your information. Very impressive cars. When the time comes I'd love to pick your brain about building an independent rear suspension as well.
     
  4. rooman
    Joined: Sep 20, 2006
    Posts: 4,052

    rooman
    Member

    I am with you on this one Unkl. I still can't see ElPolako's contention that putting the spring load on the upper arm will influence the suspension geometry re castor etc (unless the arm is pivoted on really soft bushings). In the same vein, the reason that most rod linked shock actuating systems are pushrods is related to packaging.
    With a pushrod it is easy to mount the rockers and shocks on top of the forward frame/tub area while a pull rod virtually demands that the shock be low in the frame. In center steer open wheel cars where space is at a premium and tub integrity is necessary to pass crash tests putting the big stuff up high is mandatory
    I agree that scratchbuilt should read all of Carroll Smith's books (Engineer, Tune and Prepare to Win, as well as Nuts, Bolts and Hardware) and it would probably pay to invest in William C. Mitchell's software. I have used it to design and proof the suspension on a couple of high horsepower front drive cars and both worked great (Lisa Kubo's first in the 7's Saturn was the second)

    Roo Man
     
  5. Rootie Kazoootie
    Joined: Nov 27, 2006
    Posts: 8,134

    Rootie Kazoootie
    Member
    from Colorado

    Yes, Carroll Smiths- Tune to Win and Engineer to Win- will give you the calcs for inboard ifs geometry. Always available on E-Bay for about 20 bucks and the big book stores often have them or can order them.
    Kugel Komponents has just what you need for a mere 4.5 large
     

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  6. k.cast
    Joined: Sep 14, 2007
    Posts: 1

    k.cast
    Member
    from UK

    You need Carroll Smith's books, Tune to win and Engineer to win.That should set you on the right track geometry wise and working out spring/wheel rates. Get it straight whether you NEED push rod suspension or whether you just WANT it. You can do pretty well the same job with inboard suspension and an extended top wishbone which will use a lot less parts. On an F1 car now, everything is totally subservient to aerodynamics and spring/damper units are really only a packaging problem. With a pushrod setup, you can pretty well put the damned things where you want and more importantly, out of the airstream. A slender elliptical pushrod creates a lot less drag than a coil over damper unit ever will. Do you really need it that bad. Check before designing such a set up that your dampers will operate horizontally, upside down or whatever other way you want to lie them .
     
  7. daveheld
    Joined: Oct 3, 2007
    Posts: 40

    daveheld
    Member

    JPMACHADO ( and others )
    if this is still an area of interest, let me know... I'll help out where I can.
    http://www.team321.com has some useful info.

    dave
     
  8. Joe Sulpy
    Joined: Apr 19, 2012
    Posts: 4

    Joe Sulpy

    image.jpg "Brain Damage" built by Joe Sulpy III or better known as Sr. Cantilever horizontal coil over front suspension. Designed and built in the mid 70's
     

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    Last edited: Jun 30, 2014
  9. you also have to consider anti dive. its best to make a full size mock-up and make a graf of camber, caster and toe changes as it the suspension goes through total travel
     

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