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  1. #1
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    Default Birdcage, Bar position?

    STD being the 4.5" off center, both bars.

    Speaking of the LR, what happens when you move the bar up on the BC to 5.5"?

    Considering its a zero index deal, 12 to 6 on the holes, but also fwd 1" on top, 1" behind center on the lower.

    Would moving to 5.5" on the top bar give the force generated by the rear end more leverage on the top bar ?

    Reading a lot about force based instant centers, i noticed it moves the IC aft a bit and lower, but trying to figure out other side effects.

    Thanks, Krom

    Just say no...

  2. #2
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    As you move a bar away from the axle centerline, you remove force from it.
    Droop isn't the problem.

    Arizona Speedway - 2
    Alltech -1
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  3. #3
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    Default

    Thanks, MBR.

    Brings up another question LOL.

    If it loses force, moving 1 bar out (top bar), does that force get applied to the closer to CL bar (Lower)? or does it get lost or not generated by the rear end?

    Which bar would you want to amplify the load on, another question i guess LOL. Being semi-retired these days, gives me time to ponder things, very dangerous...
    Last edited by Kromulous; 07-27-2020 at 02:35 PM.

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  4. #4
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    Default

    Quote Originally Posted by Kromulous View Post

    Considering its a zero index deal, 12 to 6 on the holes, but also fwd 1" on top, 1" behind center on the lower.
    Krom, did you say that backwards? No index is with the top bar backwards and the lower bar forward. STD is more with the bars static on cage at 12/6 ish and no index is 1/7 ish

    Quote Originally Posted by Kromulous View Post
    Would moving to 5.5" on the top bar give the force generated by the rear end more leverage on the top bar ?
    Moving the bar on the cage up to 5.5 will significantly reduce the thrust on the entire LR suspension
    Last edited by billetbirdcage; 07-27-2020 at 02:49 PM.

  5. #5
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    Default



    Blue or red lines going to black circles are the bars and the line from the intersection of those lines to the center of the axle is the thrust angle the rearend puts on the bars. This is only a drawing at ride height and dynamic will be a greater difference in thrust between the 2 (red vs blue)
    Last edited by billetbirdcage; 07-27-2020 at 03:00 PM.

  6. #6
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    Default

    So you say it reduces overall thrust on the entire LR? i have been plotting out the IC on paper today, and my DWG similar to yours shows the same, so moving that IC further aft from the BC reduces the force?

    I must be confused = nothing new there. But yes, i am 1" fwd on the top bar, and 1" aft on the lower bar. So as you described i am backwards ? BCs we have a bubble on the bottom, so i just keep the bubble centered at full droop.

    Actually i checked it and am just 1" fwd on the top bar, std on the lower.
    Last edited by Kromulous; 07-27-2020 at 03:56 PM.

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  7. #7
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    Default




    Frame side on left and cage on right

    There are many ways or things you can do here, but the general std no index deal is this ^^

    STD would have bars static close to 12/6 and more like 10:30/4:30 at full hike (close to over centering cage)

    No index would have bars static close to 1/7 and more like 11:30/5:30 at full hike (long ways from over centering)


    ***Note to move bars on cage you have to move on frame or change length of bar or you will move the rear end forwards/backwards and change the static wheel base.
    Last edited by billetbirdcage; 07-27-2020 at 04:34 PM.

  8. #8
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    Default

    Anything to gain with the zero index billet, esp on a 602 crate?

  9. #9
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    Default

    Maybe I'm missing the entire mechanics of zero index....but it still makes "zero" sense to me. Even after reading all of the threads/posts on it. How is a zero index setup any different than if I run a LR digressive stack that drops out to zero at full droop? Wouldn't a digressive stack be beneficial over zero index since it helps thrust the car up initially? Again, maybe I'm misunderstanding the purpose of zero index, but I just can't wrap my head around it.

  10. #10
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    Quote Originally Posted by HuckleberryB4 View Post
    Maybe I'm missing the entire mechanics of zero index....but it still makes "zero" sense to me. Even after reading all of the threads/posts on it. How is a zero index setup any different than if I run a LR digressive stack that drops out to zero at full droop? Wouldn't a digressive stack be beneficial over zero index since it helps thrust the car up initially? Again, maybe I'm misunderstanding the purpose of zero index, but I just can't wrap my head around it.
    The closer you come to over indexing, the more you have mechanical antisquat. The suspension loses more and more compliance. Your tire becomes all the suspension. Your suspension becomes useless.
    Droop isn't the problem.

    Arizona Speedway - 2
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  11. #11
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    Then is mechanical anti-squat a bad thing? to some extent? I am gonna say that it is a typical race car deal, its good and bad, just what can you live with kinda thing.

    My question is on zero index deal is how much load is on the LR tire, via bar angle (mechanical leverage) via rear end thrust applied thru the IC's or droop load?

    IF your digressive, and zero'd out on droop load (at full hike) its all mechanical, via bar angle, applied by the rear ends force. So that would mean you would have some mechanical anti squat, i guess the secret is calculating that number and knowing where you need to be on given track conditions, or am i in left field?

    Because i have not gotten to work well so far, but i keep trying LOL...

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  12. #12
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    Quote Originally Posted by Kromulous View Post
    Then is mechanical anti-squat a bad thing? to some extent? I am gonna say that it is a typical race car deal, its good and bad, just what can you live with kinda thing.

    My question is on zero index deal is how much load is on the LR tire, via bar angle (mechanical leverage) via rear end thrust applied thru the IC's or droop load?

    IF your digressive, and zero'd out on droop load (at full hike) its all mechanical, via bar angle, applied by the rear ends force. So that would mean you would have some mechanical anti squat, i guess the secret is calculating that number and knowing where you need to be on given track conditions, or am i in left field?

    Because i have not gotten to work well so far, but i keep trying LOL...
    When your chain is tight, there is no relative motion. That means the sum of all forces is zero. The only load is the weight you lifted.

    Go back and watch guys hit a hole at Eldora in 2014. They may bounce 4 times. That ain't fast.
    Droop isn't the problem.

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  13. #13
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    Tader has a pretty good video on Racer Know How.

    Its gotta help some when at full droop, the heims on the trailing arms are very free and not bound up!

  14. #14
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    Quote Originally Posted by HuckleberryB4 View Post
    Maybe I'm missing the entire mechanics of zero index....but it still makes "zero" sense to me. Even after reading all of the threads/posts on it. How is a zero index setup any different than if I run a LR digressive stack that drops out to zero at full droop? Wouldn't a digressive stack be beneficial over zero index since it helps thrust the car up initially? Again, maybe I'm misunderstanding the purpose of zero index, but I just can't wrap my head around it.
    To simplify it a little further. Plain and simple if the bars get close to over indexing (flipping the bird cage) the suspension goes ridged. Kepping aero out of the equation This creates max traction. on a smooth surface but on a rough surface it will cause the car to bounce and you can't have traction when your tire is off the ground. Also when the lr suspension goes ridged your spring rate is infinite you cant tune that so all these fancy digressive stacks become less or not effective

  15. #15
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    Default

    What if you lower the lower bar to 5.5 will that move the thrust back fwd?

  16. #16
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    Yeah i would like to know that to Hunterracing, its something i havnt gotten a lot of answers on so just gonna try it LOL!

    Also, if these are the bar postions for zero index, top back, bottom fwd, then what is it that the XR1s are running? The ones i look over, the top bar is fwd, and the bottom bar is aft. Seems like that would still be a zero index deal, with a shorter steeper instant center, and thrust angle?

    Just say no...

  17. #17
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    I would think if you raised top to 5.5 then lowered the bottom to 5.5 it would kinda equal it self out but guess depends on bar location on frame but not sure Iím right bout it. Wehrs saids raising on cage to 5.5 upper will make tighter in and looser off

  18. #18
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    Quote Originally Posted by Kromulous View Post
    Yeah i would like to know that to Hunterracing, its something i havnt gotten a lot of answers on so just gonna try it LOL!

    Also, if these are the bar postions for zero index, top back, bottom fwd, then what is it that the XR1s are running? The ones i look over, the top bar is fwd, and the bottom bar is aft. Seems like that would still be a zero index deal, with a shorter steeper instant center, and thrust angle?
    Ignore where the bolt is compared to other holes. Where are the two birdcage attachment points in relationship to each other? Don't forget the coilover attachment point is working in an arch too.
    Droop isn't the problem.

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  19. #19
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    Default

    I've been playing with this a lot in the shop lately. Isn't the point of zero index to get more bar angle without over indexing?

  20. #20
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    Yeah, and to keep some compliance with the shock to the track, keep rubber on the road so to speak.

    I mapped it out on paper, and the XR1 way seems to allow you more upper bar angle, and still be zero index. It brings the Instant center closer to the rear end, and more upward angle. Plus less lower bar angle, which potentially could allow you to run more droop overall, or with less rear steer. Bar lengths would change, 1" longer lower, 1" shorter upper, so the split in lengths could be closer if you wanted that, depends on your 4 bar plates.

    Or am i off in my thinking? LOL wont be the first time...

    Just say no...

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