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4-link debate

Discussion in 'The Hokey Ass Message Board' started by sideweeler, Apr 4, 2013.

  1. CutawayAl
    Joined: Aug 3, 2009
    Posts: 2,144

    CutawayAl
    Member
    from MI

    Keeping the arms parallel minimizes binding of the suspebsion when one wheel tries to move up or down relative to the other, as happens on cars that turn corners and drive on bumpy surfaces. Angling the arms relative to each other, as is done on drag cars, results in geometry that is essentially the same as what ladder bars provide. Adjusting the links on a drag car is functionally the same as changing the length and/or front mounting poit of a ladder bar. That suspension is basically a hinge. Fine for going straight, bvad fior anything else. Like ladder bars, when the links aren't parallel something has to flex, or bend, or have compliant mountings, to accommodate independent wheel movement.

    With drag racing suspension there is a momentary upward force on the chassis. Where on the chassis that force is concentrated depends on how the suspension is set-up and adjusted. Beyond that, the only way for a torque are to lift the front of the car would be if the wheels were held from rotating. Wheelstands are a function of where the car's GG is relative to the rear wheels, and how hard the car accelerates. Wings probide downforce, but that also have drag. The higher a given wing is mounted, the more weight it takes off the front end of the car. It the same principal with air(center of pressure) as with the CG.
     
  2. I've been building and tuning drag cars for 20 years, and I own and race my own supermodified (like the car pictured above). My observations come from a thousand nights at the race track over 30+ years, not from something that turned up on a Google search.

    As I mentioned in my first post on this debate, your conclusions are 100% correct in the case of an independent suspension; where the ring and pinion are not connected to the drive hubs by a solid axle tube.

    As far as a solid axle goes, I guess we will have to agree to disagree about the upper links (which, by the way, I noticed you switched to LOWER links...).

    Carry on.
     
  3. tikiwagon13
    Joined: Feb 23, 2011
    Posts: 371

    tikiwagon13
    Member

    Is this turning into arguing for the sake of arguing?
     
  4. 73RR
    Joined: Jan 29, 2007
    Posts: 6,326

    73RR
    Member

    Been lurking, but have to comment on that video...crazy amount of movement going on there. Who had the idea to mount the camera ?
    As for suspension designs, I think that I'll stick to parallel leafs like MotherMopar used for decades...:p

    .
     
  5. I was surprised that it is set up so the right rear spring actually dangles completely free at extension
     
  6. Pops1532
    Joined: Jun 19, 2011
    Posts: 544

    Pops1532
    Member
    from Illinois

    I've seen cars run many laps without the LR spring after breaking the limit cable and spitting the spring out.
     
  7. blowby
    Joined: Dec 27, 2012
    Posts: 6,592

    blowby
    Member
    from Nicasio Ca


    Great video. I know nothing about those suspensions but I was watching some of the videos that came after and noticed the rear end housing seems to float in outer mounts that link to the chassis. So are we really watching an upper link as would be in a regular 3-4 link?

    As in this one:

    http://www.youtube.com/watch?v=65hOTt4EDvA&list=PLE2ABA35D0392CD3D
     
  8. sideweeler
    Joined: Sep 28, 2010
    Posts: 127

    sideweeler
    Member
    from searcy AR

    I just want to thank everyone that contributed to the tread. I hope that I haven't pissed anyone off during this discussion, and if I have, I do apologize. I understand what you guys are saying (even though it took me a while). So the upper links ARE going to be redone.
     
  9. sweeden
    Joined: Mar 25, 2013
    Posts: 165

    sweeden
    BANNED

    I have been into mini trucks for a long time and I know most of us run triangulated 4 links and everyone mounts them at an angle like that. the issue with the parallel links seems to be that u always need to run a pan hard bar on the back so I know I and most everyone I know stays away from them on the rear end.
     
  10. I think in the long run you'll be glad you did. ;)
     
  11. The "floaters" remove the pinion rotation torque from the outer links and place it on a top link (as in the video I posted) or a torque arm. This technology is pretty much limited to dirt circle track cars, so I didn't really go into it in any detail. The floater links DO provide a large amount of thrust anti-squat (as Kerry was describing) on all 4 links, but this would NOT be the same reaction if the brackets were welded to the housing as we see on a street or drag car. The PULL effect then moves to the top outer links.
     
  12. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,951

    gas pumper
    Member

    Maybe not so fast. What's wrong with a little roll stability? If that's what the parallel mounts and angled rods give you.

    Here's some prior design. First used in 1953. And continued on subsequent versions to the late 70's. Also air ride. Parallel lowers, angled uppers, rubber bushing mounted. The anchor ends on the framework were in vertical alignmet, upper and lower. The upper bars went to the top of the pumpkin.

    These pictures are from a 1953 Maintenance Manual for PD-4104 buses. Third picture is a detail of the rod end-bushing asembeled.
     

    Attached Files:

  13. Note in picture 1 that the angled links are connected on a very short common shaft and are very close together. MUCH less relative motion in roll than you would get with them mounted on the axle tubes outboard of the center section. In that case, the bushing flex is adequate to the task.

    You CAN NOT generalize this stuff. The variations in EACH application must be considered to decide whether or not a design is suitable.
     
  14. dano1930
    Joined: Feb 10, 2013
    Posts: 58

    dano1930
    Member

    I have been following this thread and read all the responses I think your making the right decision.
     
  15. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,243

    Hackerbilt
    Member

    Exactly. The OP's design can certainly work and work well...just not with the bushing design his arms use.
    The bushings/bushing tubes are too wide and the bushings can't squish enough to allow for easy articulation.
    With the right bushings etc it can work fine...just not really any better than the usual angled mounting way that uses the "normal" bushings.

    In the bus suspension schematic...can someone explain why the bushings and outer bushing tubes are designed to be tight at the center of the bushing but taper off at an angle as you reach the outer edge of the bushing tube?

    It's one of those variations to make a design suitable that exwestracer is talking about. ;)
     
  16. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,284

    Kerrynzl
    Member


    When you get torque reaction from the pinion [ which is always less than axle torque due to gear ratios ] this reduces forward compression loads on the uppers and increases forward compression loads on the lowers.
    When I say "reduces compression loads" it never puts the uppers into tension while the vehicle is ACCELERATING forward [from the axle centreline ]
    The floaters [ or birdcages ] in the video disconnect the pinion torque reaction from forward compression loads of the Upper and lower linkages.
    The compression loads during acceleration are clearly visible on the LH linkages of the first video.[ they create a lot of lift at the axle ]
    The laws of physics do not change because the vehicle changes from IRS to 4-link

    On another thread here you claim you are "a chassis builder and teacher"
    Well if you think this theory is wrong Why don't you teach us something you think we don't know. [ instead of trying to trip people up by pulling 1/2 quotes out of text ]
     
  17. I love these threads, I learn a ton from them.
     
  18. CutawayAl
    Joined: Aug 3, 2009
    Posts: 2,144

    CutawayAl
    Member
    from MI

    While you are entitled to your opinion.......
    - Although experience is valuable, it isn't the same thing as knowledge.

    - When a person assumes they understand something that they don't, they aren't in a position to learn.

    - For reasons unknown some of your comments have been needlessly defensive.

    - You have been given good info. Whether you chose to ponder and understand, or dismiss, is up to you.
     
  19. ago
    Joined: Oct 12, 2005
    Posts: 2,200

    ago
    Member
    from pgh. pa.

    The tapered bushings in the bus diagram are interesting. The bushing could be machined out of Teflon which is self lubricating. Maybe a little stiff. Any ideas on another plastic that machines well?


    Ago
     
  20. Agreed! Makes you realize how much goes on with suspension that most would never think about.
     
  21. EXracer64
    Joined: Dec 7, 2011
    Posts: 226

    EXracer64
    Member
    from nj

    Not sure if this was covered, but the triangulated setup also locates the rear centered under the car, where a parallel setup needs an extra bar to locate and center it.
     
  22. EXracer64
    Joined: Dec 7, 2011
    Posts: 226

    EXracer64
    Member
    from nj

    Soft springs do not aid traction. If a spring is soft, the transfer of weight is compressing the spring instead of being on the tire. Anytime a car launches and the body seperates or squats, its wasted energy.
     
  23. I think the biggest lesson learned, for me at least, is that just because it works doesn't mean it's correct.
     
  24. blowby
    Joined: Dec 27, 2012
    Posts: 6,592

    blowby
    Member
    from Nicasio Ca

    I think he was talking about front springs? Here is the full quote:

     
  25. EXracer64
    Joined: Dec 7, 2011
    Posts: 226

    EXracer64
    Member
    from nj

    Yea your probably right. I apologize if so.
     
  26. 73RR
    Joined: Jan 29, 2007
    Posts: 6,326

    73RR
    Member

    Delrin is a common industry 'plastic', as is UHMW. Both machine well.

    .
     
  27. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,951

    gas pumper
    Member

    Just to answer the bus bushing questions.

    The early versions had the split bushings of soft rubber. Later versions used a one piece bushing that was figure 8 shaped and still soft rubber. When polyurethane became popular in the 80's(?) aftermarket suppliers like Energy Susp made split hard poly bushings for this application. They held up really well, but were expensive so we just used them on the rear lowers.

    The figure 8 shape, I think, was to allow for the twisting and bending that happens when the susp moves a lot. and these things had about 6 inches of susp travel.

    Front susp was a parallel 3 link with a lateral (panhard) bar. Bushings lasted almost forever. Real long life. The rear had all the power and most of the braking and the bushings would take a beating, lowers more than uppers. Maybe once a year replacement (50,000 to 100,000 miles)(city use more often than highway). The rubber would fatique and split apart and spit the bushing out.

    Thanks ExWest, I see the difference from the orig. pictures at the begining of the post. The bus version is almost like a triangle upper compared to that.
     
  28. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,243

    Hackerbilt
    Member

    The bushings are tapered to allow additional twist in the bushing so the axle can articulate a little better, but still have limited deflection front and back as the axle tries to roll under torque.
    Teflon and the like would defeat the purpose.
     

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