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Technical Triangulated 4 link anti squat?

Discussion in 'The Hokey Ass Message Board' started by rawcjw19, Sep 13, 2017.

  1. rawcjw19
    Joined: Oct 8, 2012
    Posts: 391

    rawcjw19
    Member

    [​IMG][​IMG] I need a little suspension help. What do I need to do to get less squat on hard launches? I am running a triangulated 4 link similar to the picture, with qa1 promastar coilovers. Car drives straight ,handles well. I have put a little heavier spring in and it rides pretty good. Any suggestions?


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  2. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 5,267

    mgtstumpy
    Member

    Just me but I'd double sheer the lower arms for insurance if possible as well as swapping in heavier springs to minimise squat. Maybe just winding the passenger side up for hard launches and resetting it for normal driving? It may not be an issue however I would ensure that the lower arms point up at the front and not down. If down slightly it will cause the body to squat. The torque is apparent, lifting the front driver wheel which in turn causes weight transfer into the body.
    I know down here in my state, 'A' frames need to have a 'K' member for strength and to minimise torsional twisting. A frame with only ladder cross members is more susceptible to twisting than a frame with one installed. My 2c worth.
     
  3. rawcjw19
    Joined: Oct 8, 2012
    Posts: 391

    rawcjw19
    Member

    Thanks,It is a tubing frame with k member. I am not sure what you mean by double shear the lower arms? I thought I might try to shorten the upper passenger link a couple turns?


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  4. models916
    Joined: Apr 19, 2012
    Posts: 341

    models916
    Member

    Lower the front of the upper arm about an inch. Heavier spring may just make it bounce off the ground but try that anyhow. Nice rod.
     
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  5. PCJ
    Joined: Mar 19, 2010
    Posts: 23

    PCJ
    Member
    from Austin, Tx

    double sheer would be having a bracket on both sides of the link attachment points with 24th bolt ruining through all of it like in the diagram. Single sheer is just a tab on one side of the end link which is the way it appears to be setup in the pic of the car

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  6. rooman
    Joined: Sep 20, 2006
    Posts: 2,577

    rooman
    Member

    mgtstumpy is referring to the fact that your lower arm is hanging off the side of the bracket with no support. It is not obvious in the photo but I presume that it is a regular tri four link bracket with a sleeve through a pair of brackets that hang off the lower frame flange. On a regular street application it is not usually a problem but those big tires on your car are putting a lot of load on the bolt.
    As for getting rid of the squat, models916 has the right idea but I will bet that you don't have any adjustability in that area.

    Roo
     
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  7. yellow dog
    Joined: Oct 15, 2011
    Posts: 314

    yellow dog
    Member
    from san diego

    There are several good calculators online. Input your existing parameters to see where your IC and antisquat are at currently. By the looks of the picture, you are likely under 100%. When you fix the LCA to be in double shear, fabricate the bracket with additional holes to allow some adjustment
     
  8. rawcjw19
    Joined: Oct 8, 2012
    Posts: 391

    rawcjw19
    Member

    Thanks for the ideas. Rooman you are correct.boughten lower bracket from Pete and Jakes. All the other brackets are supported on both sides.


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  9. Lowbuckboz
    Joined: Apr 2, 2008
    Posts: 477

    Lowbuckboz
    Member

    You could use a good anti roll bar kit. That will take the twist out. Not good for street driving, as it doesn't allow for much articulation.

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  10. rawcjw19
    Joined: Oct 8, 2012
    Posts: 391

    rawcjw19
    Member

    I am pretty tight on space to move the upper arms much


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  11. rooman
    Joined: Sep 20, 2006
    Posts: 2,577

    rooman
    Member

    I presume that the car spends most of its time on the street so I would think about adding some preload to the right rear spring for track outings. With your adjustable shocks bump the compression damping up as well. Changing the mount heights of a triangulated four bar can have a detrimental effect on street driveability if you move them enough to really make things better at the track. Lowbuckboz is also on the money in that an anti roll bar stiff enough to work at the strip is going to be overkill on the street.
    No matter what you do spring and shock wise that blown motor is going to make enough torque to rotate the car on its longitudinal axis so unless you re-engineer a lot of suspension stuff ( race car style four link, anti roll bar etc) that will have an adverse effect on streetability you are going to have this problem. It looks like it is leaving pretty well to me for what you have.

    Roo
     
  12. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 1,879

    Bandit Billy
    ALLIANCE MEMBER
    from Washington

    My OT Olds has the same suspension. It digs off the line. Box the trailing arms, top and bottom. Like this example I stole off the internet. Add Polyurethane bushings while you are at it.
    upload_2017-9-13_13-31-52.png
    Also, I added QA-1 shocks with adjustable rebound and compression with adjustable coil overs. Factory rear anti sway bar with welded in bushings in the trailing arms to prevent collapsing.
    upload_2017-9-13_13-34-5.png
    The car is OT like I said but from this angle I thought it was more help than hindrance. If I am wrong it can be deleted without insult but I can fix that dive problem you have with these steps.
     
  13. Relic Stew
    Joined: Apr 17, 2005
    Posts: 1,042

    Relic Stew
    Member
    from Wisconsin

    The links need some angle to each other from the side view. Think of it as a virtual ladder bar. The shorter it is, and/or the higher the intersection point, the more it will lift the body under acceleration.

    Moving the links will likely also change the roll axis, so it needs to be thought out/calculated to be done properly. Moving the front of the upper arms down has less detrimental effects than moving the front of the lowers up.

    Anti-squat geometry takes some of the acceleration weight transfer load off the springs and puts it through the links. It can increase traction, as the load transfer is instant, rather than taking time to compress the springs. However, this will stiffen the suspension, since the load is not on the springs. If your launch area is rough, this can actually decrease traction, as the suspension will not respond as easily, and bounce on the tires.

    anti-squat.gif
     
    Last edited: Sep 13, 2017
  14. lostone
    Joined: Oct 13, 2013
    Posts: 217

    lostone
    Member
    from kansas

    Agree with the above, leave lower arm level with the ground, drop upper arm an inch in the front. You always want (99.9%) the lower parallel with the ground, 4 link, ladder bar etc. Your adjustment is made with the upper to change your instant center.
     
  15. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 1,251

    Kerrynzl
    Member

    Doing this gives the opposite of what the OP is trying to achieve!
    Lowering the front uppers ends up lowering the instant centre which creates more squat.[less anti-squat]

    The problem with unequal length bars [viewed from the side] is the short upper bar will lower and shorten the instant centre drastically when the rear suspension compresses. [dynamic instant centre]

    Be careful when playing with anti-squat [eg: raising the front/ lower arms etc] this can promote "roll oversteer" which can be dangerous.
    I would lengthen the upper bars first.

    Stiff rear springs help control weight transfer and will plant the tyres harder with less given spring compression.
    All springs have a point of equilibrium where the load and stiffness equalize. with soft springs they will compress more for the same given load.
     
  16. http://performancetrends.com/4link.htm

    Here is a link to a program to work this out. Use the google "4linkcalculator" or something along those lines. Some clever guys have put together some nifty programs to theorize with. You'll find a ton of info linking to Pirate4x4.com. Don't let that dissuade you, the numbers are just numbers whether for a lifted 4x4 or car, just use the program to get the desired effect you want. So much info goes into tuning this set-up. Center of gravity, driveshaft information, spring length/rate...

    Another link to an online one. I didn't realize the first link was a pay to play deal sorry. http://www.shopeshop.org/tim.39.htm
     
    Last edited: Sep 13, 2017
  17. rooman
    Joined: Sep 20, 2006
    Posts: 2,577

    rooman
    Member

    Thanks Kerry--glad that somone else sees the big picture re overall chassis dynamics. What works on the track usually does not help on the street.

    Bandit Billy, I presume from looking at the rest of the car and the OP's comment about shortening the upper arms a couple of turn that the upper arms are tubular hot rod style parts rather than OEM stamped pieces.

    Roo
     
  18. wicarnut
    Joined: Oct 29, 2009
    Posts: 1,665

    wicarnut
    Member

    From pic, looks good, front up, going straight, thinking your frame is twisting from torque, model A frame boxed ? Nice Ride ! Looks like FUN to me.
     
  19. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 1,251

    Kerrynzl
    Member

    Thanks for the vote of confidence mate!
    What people need to understand is the instant centre is the theoretical point of thrust [or acceleration]. It has nothing to do with torque reaction.
    If the instant centre is below the centre of gravity, the car will transfer weight onto the rear wheels via "overturning moment" or Squat.
    This squat is controlled by spring stiffness, so the OP was correct in using stiffer springs. [some drag cars have solid rear suspension]

    Now there is another factor to consider here [AND very noticeable in the OP's photo].
    As well as weight transfer onto the rear wheels, there is driveshaft torque trying to lift the RR tyre [causing the RR suspension to compress] and Engine torque reaction down through the frame [also causing the RR suspension to compress]
    Which is why the car is leaning over on launch

    To get the car to launch straight would require a correction RR ride height [ use a preloaded or weight jacked spring]

    These should be set on scales so the static corner weight is preloaded on the RH side, but during hard acceleration there is even spring stiffness on both rear wheels [it will still go straight]

    For a dual purpose car , I would simply bolt in another RR coilover for racing while changing to drag slicks.
    The frame is not twisting in the OP's car. [the visor is parallel with the spreader bar], The twist is in the RR suspension.
     
    Last edited: Sep 15, 2017 at 5:06 AM
  20. rooman
    Joined: Sep 20, 2006
    Posts: 2,577

    rooman
    Member

    ^^^^^^^^ Yep! I usually like to see about 40-60 lbs preload on the right rear (and even on a rigid rear car a bit of preload is usually needed).

    Roo
     
  21. shtboxyj
    Joined: Sep 8, 2017
    Posts: 6

    shtboxyj

  22. saltflats
    Joined: Aug 14, 2007
    Posts: 6,623

    saltflats
    Member
    from Missouri

    If the battery is mounted in the right rear move it to the left side.
     
  23. Dreamweaver
    Joined: Feb 26, 2003
    Posts: 912

    Dreamweaver
    Member

    Nice tudor!

    How about more info and pics? What kind of times do you run?
     
  24. rawcjw19
    Joined: Oct 8, 2012
    Posts: 391

    rawcjw19
    Member

    Sorry been busy haven't had a chance to get back on here. I will get some pics tonight. Can't move my battery it was tight fitting it on the right side.no room on left,design flaw by me. I haven't had the chance to put it on the scales again maybe this weekend. I did manage to change a blower pulley. Doubt that helps with this problem went from 5#boost to 8. I will dig out a time slip. Best was 11.03 at 122 in 1/4 before the boost change


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