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Anti-Squat? - In a FRONT suspension..... 3-Link?

Discussion in 'The Garage' started by Greg72, Aug 17, 2003.

  1. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    OK so I understand (at least partially) the concept of rear anti-squat in a multilink rear suspension, and how the angle of the links will increase/decrease it's effect.


    My question is whether this same consideration is important on front suspension also? (Do you still call it "anti-squat"? or "Anti-lift"?) /forums/images/graemlins/smile.gif

    Most of the linked front suspensions I've seen (JuanBlazer is the exception) were a 3-link setup. Based on the limited number of spots available for the links (lots of stuff in the way up front!) it seems like the links will go as far outward on the axle tubes as possible (to create a slight inward taper of the links)....and the other end will end up roughly in line with the framerails underneath???

    The use of LONG links up front can provide a shallower angle for the links, but I'm guessing most of the 3-Link setups are probably in the 32" to 36" link length range....?

    Anyone want to offer some advice on "front antisquat" or on the lengths of front links they've seen?
     
  2. m j

    m j 1/2 ton status

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    most books think 2wdr
    so the front is refered to as antidive, as in brake dive
     
  3. Triaged

    Triaged 1/2 ton status

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    You will never read anything in books about anti squat for the front. They all talk about anti lift (this only applies when the front axle is under power) and anti dive (a bit more messy of an equation because of needing to know-guess-the front to rear brake bias).

    I think for the front it is safe to say you want to keep the anti dive as low as possible (as in nowhere nere 100%). Having the wheels move forward on compression isn't the best geometry for wheeling. This is one of the reasons that the jeep guys swap the shackle from the front of the leaf to the rear.

    Do you have all the equations?

    To me a 3 link is the way to go up front. It does have some drawbacks but IMO less than other setups.
    Depending on where you put the "3rd" link you will cancle out more or less "torque roll" from the truck but it will all come back under breaking. If you put the "3rd" link way over to the side (i.e. a radius arm on one side and a link on the other) you will get no torque roll (which all trucks have from the factory) under acceleration (at least from the front). However under breaking all that torque roll (and more) that you got rid of under acceleration will come back (and the truck will lean the other direction).

    All this is only hinted at in "Race Car Vehical Dynamics" at the bottom of page 653.

    [ QUOTE ]
    The third link is ofter mounted in the center of the axle. Another option is to mount it off to the right-hand side of the center. If can be shown that if the offset distance is in the correct proportion to the axle ratio being used, the load on the tires will remain equal under acceleration and the sprung mass will not roll. Under braking there will be a slight tendency to roll to the right, however.

    [/ QUOTE ]

    In order to make the truck handle the street will you need to worry about breaking in the front more than acceleration torque reaction as it will be in 2wd while on the street. I guess what I am trying to get at with all this BS is keep it as close to the center as you can.
     
  4. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Dan,

    I've got the Milliken book, and the Herb Adams book...

    The tough part is finding references to SFA suspension design (gee, I wonder why?) in racecar books.

    I'll go back and reread the section of Milliken you mentioned to look for clues.


    So are you saying that "anti squat" (rear) = "anti-dive" (front).....as in, angling the links more severely up front is GOOD? Or are shallower angles how you increase anti-dive...?


    /forums/images/graemlins/thinking.gif




    ps. Interesting point about the 3rd link.....if I can just figure out a way to run my engine with NO oilpan, I should be able to center that link quite nicely!!! /forums/images/graemlins/grin.gif
     
  5. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    There are too many constraints to worry about the placement of the single upper link, it really only goes one spot, along side the starter in my case, or next to the oil filter with a GM front axle.
    I didn't worry about the squat/dive characteristics at all on my front, I had to build it around the front driveshaft and other concerns were secondary to keeping the driveshaft happy. With a low pinion axle, you may be in the same situation.
    I don't look at the torque reaction on the front as being something you can count on, the only place you really need the traction to create a stabilizing force is climbing at you probably won't have enough traction from the front to get a big reaction force, and if you do get it too hook up, it probably won't stay that way for long.
    In general I think a somewhat neutral reaction is best, for front or rear. If your suspension linkage is putting big ride height change inputs to the chassis, you could cause problems as you gain and lose traction. You can also make the suspension very stiff under acceleration or braking conditions. It is kind of cool having the front linkage cancel some of my brake dive but in the extreme case, you could make the suspension so stiff on braking that you sacrifice some vehicle control to bouncing around.
     
  6. Triaged

    Triaged 1/2 ton status

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    Anti-Dive is almost just Anti-Squat turned around. It just has a factor in there for brake bias. It might be easier to think about the front doing 100% of the braking to make the equations a bit easier to mess with initially (you don't really know what the ratio is anyway...so just ignore it).

    [ QUOTE ]
    So are you saying that "anti squat" (rear) = "anti-dive" (front).....as in, angling the links more severely up front is GOOD? Or are shallower angles how you increase anti-dive...?

    [/ QUOTE ]

    I am of the opinion that you want as close to ZERO % anti-dive as possible. As Watson said you won't be able to obtain this and still have a driveshaft going to the front axle. To do this you would want your IC to be as close as possible to the ground...not exactily obtainable either. Try to get the front link as flat as possible (even angling down from the front if you can) and the upper has to go where it fits.

    You ought to start out by finding out where the leaf spring suspension you have now ends up. The IC will be above and in front of the axle. To think about it like a link suspension rotate it 180 degrees and keep the distance from IC to axle the same. This won't help you with wheel travel arc or pinion angle change but it will at least tell you where the steady state anti-dive is at.
     
  7. m j

    m j 1/2 ton status

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    can you make an image that explains the math of straight axle anti dive.
    I make too many assumptions to trust what I came up with
     
  8. Twiz

    Twiz 1/2 ton status

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    Cool topic!

    I wonder if useing 2wd A-arm dimentions would be helpfull in finding the trailing arm locations. (I might be up-in the night here)

    You can "see" anti-dive characteristics dialed into the front A-arms.
    When viewed from the side, the upper and lower frame mounted pivot points are not parallel, they are slightly tapperd to the rear. If you continued the pivot point along the same plane, rearward to whatever length needed. And made your trailing arms (or links) mount to the frame in that location. You would, retain the factory set anti-dive characteristics.
    Why re-invent the wheel when it's allready been done ?

    *Edited*
    Crud, that wouldn't work, the fame would be resting on the axle houseing.
    So much for that idea.
     
  9. Triaged

    Triaged 1/2 ton status

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    This is mostly out of "RCVD". They do not have a diagram & equation for anti-dive with outboard brakes...just one that will tell you the "lift force".

    As webshots does not allow direct linking just cut and paste this into your browser.



    http://community.webshots.com/s/image7/6/83/60/86168360AIMVrm_ph.jpg



    [​IMG]



    As a side note for this discussion Pinion (or driveshaft)Brakes count as "outboard brakes".
     
  10. Donovan

    Donovan 1/2 ton status

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    [ QUOTE ]


    Most of the linked front suspensions I've seen (JuanBlazer is the exception) were a 3-link setup. Based on the limited number of spots available for the links (lots of stuff in the way up front!) it seems like the links will go as far outward on the axle tubes as possible (to create a slight inward taper of the links)....and the other end will end up roughly in line with the framerails underneath???


    [/ QUOTE ]


    I believe that the links should be parallel to the frame if you are using a panhard rod. You will not get roll steer if you have parallel links unlike links that are tapered out.
     
  11. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [ QUOTE ]
    This is mostly out of "RCVD". They do not have a diagram & equation for anti-dive with outboard brakes...just one that will tell you the "lift force".

    As webshots does not allow direct linking just cut and paste this into your browser.

    http://community.webshots.com/s/image7/6/83/60/86168360AIMVrm_ph.jpg

    As a side note for this discussion Pinion (or driveshaft)Brakes count as "outboard brakes".

    [/ QUOTE ]

    Dan,


    Forbidden
    You don't have permission to access /s/image7/6/83/60/86168360AIMVrm_ph.jpg on this server.
     
  12. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Alright....I know I'm opening myself up to criticism by doing this but I'm posting a link to a series of pictures that I've taken now that I've started on a full-size mockup of a new drivetrain/suspension layout:

    Here's a "teaser shot"....

    [​IMG]


    ....and the rest of the images are below:

    Greg's Latest Ideas...


    It's always risky posting up "in process" stuff, since I'm sure you can find mistakes or things that will need to be refined further. But I value your opinions and input....so go ahead and take a look, and let me know what you think so far.

    Everything is strictly "bolt on" so far, so nothing that done cannot be "undone" if it fails the scrutiny of CK5!!! /forums/images/graemlins/grin.gif

    /forums/images/graemlins/thinking.gif
     
  13. marv_springer

    marv_springer 1/2 ton status

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    Cool! /forums/images/graemlins/cool.gif

    When I was mocking up my suspension on the Buggy, I found it useful to use 1.5" wooden dowell rod and cut it to size, drill it out w/ a 3/4" drill bit, and then "split it". Then a hose clamp can cinch it around a 3/4" heim joint.....

    I don't know what kind of body you're gonna put on that, but I'd advise taking your rockers as high as you can. Even if it seems kinda rediculous - the higher the better! /forums/images/graemlins/laugh.gif

    Marv
     
  14. marv_springer

    marv_springer 1/2 ton status

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    [ QUOTE ]
    *Edited*
    Crud, that wouldn't work, the fame would be resting on the axle houseing.
    So much for that idea.

    [/ QUOTE ]

    Ha! /forums/images/graemlins/rotfl.gif.... I love it!... Creative thinking at it's best. Twiz... I don't know how many times I've done this exact same thing in my mind..

    Marv
     
  15. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    I'm no expert by any means, but it seems like a nice set up for a full size would be springs in the front to keep roll, dive, etc. to a minimum and keep contol during climbing/desent with the rear linked up would be ideal, am I wrong in this thinking?
     
  16. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    Leaves front, coils rear would work out fine. I like the coils in the front for the ride and steering control, it also gets rid of whatever spring wrap you have from the front springs.

    Good luck trying to keep the angle on the links down, between ground clearance and motor/frame clearance, it's hard to get the vertical separation on the links and not drag them on the rocks. I could stand stretching mine by a few inches, they rarely drag but they were set by the available length for the upper link and the pinion angle control necessary.

    I'd say work on keeping the links flat and controlling your pinion like you want it, then let the anti-squat be what it is.
     
  17. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

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    [ QUOTE ]
    I could stand stretching mine by a few inches

    [/ QUOTE ]
    /forums/images/graemlins/eek.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
     
  18. Triaged

    Triaged 1/2 ton status

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    I guess you missed this /forums/images/graemlins/rolleyes.gif

    [ QUOTE ]
    As webshots does not allow direct linking just cut and paste this into your browser.

    [/ QUOTE ]

    at least I know you actually read everything I type /forums/images/graemlins/tongue.gif

    Try this one on for size.
    http://community.webshots.com/photo/20225580/86168360AIMVrm
     
  19. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [ QUOTE ]
    I guess you missed this /forums/images/graemlins/rolleyes.gif

    [ QUOTE ]
    As webshots does not allow direct linking just cut and paste this into your browser.

    [/ QUOTE ]

    at least I know you actually read everything I type /forums/images/graemlins/tongue.gif

    Try this one on for size.
    http://community.webshots.com/photo/20225580/86168360AIMVrm

    [/ QUOTE ]

    I don't usually give up that easy.....

    I tried the lazy way.....clicked hyperlink (no worky)

    Then I tried the "Open this Link in a new window" thinking that is the same as copying the URL manually (no worky)

    I guess I still have MUCH to learn... /forums/images/graemlins/thinking.gif


    Please update your pic though....this needs more STUFF!
    [​IMG]
    Please add all the new box tubing like in the photos in this thread, and then do a bunch of cool calculations and stuff....and post up data and lots of formulas with sigmas and thetas and tangents in them!!! /forums/images/graemlins/laugh.gif


    ps. The new link works GREAT by the way....."File, Save Image As...." /forums/images/graemlins/thumb.gif
     

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