Swing Arm/Z Link Basic Questions

[SweetBabyJames]

Hello,
I recently bought a used swing arm modified, and am new to this type of suspension (only ran leaf springs before). I have a few questions trying to figure this out, any help would be appreciated.

1. First of all is my terminology correct - Is the difference between "swing arm" and "z link" the placement of the springs? If the springs are located on the lower radius rod its a swing arm, and if they're on the axle tubes it's a z link?

2. Are there advantages/disadvantages to having the springs attached to the radius rod vs the axle tube, and vice versa?

3. If the purpose of a swing arm/z link suspension is to keep the rear end centered during suspension travel (fore and aft) unlike a 4 bar setup, how does adjusting the bar angles affect the handling? What is the affect with each bar: LR lower, LR upper, RR lower, RR upper.

4. Similar to my previous question, how does changing bar length affect handling?

Again, I appreciate any feedback you may. I am trying to get a grip on how to make adjustments. Thanks!

[dualdj1]

1) Yes.

2) Zlink (axle mount) is roughly half the effective spring rate of swingarm mount. If you're running a 400 on the swingarm, moving to birdcage you'd need a 200 for the same rate. Typically zlink is mounted with springs at an inward angle. this changes reaction timing of the springs as well, due to lateral movement of the axle. Because of the nature of dirt cars and the way the axle moves, many use a combination of swingarm left side, zlink right side, with good results.

3) The purpose of your bars is not to keep the axle center, but to affect the handling characteristics of your axle and apply forces to the axle, same as 4 bar. it just applies the forces in a different manner than 4 bar. They do affect your front to rear location of the axle, same as 4 bar. Your panhard bar affects side to side location of the axle.

Most of the time once you get initial setup, you don't mess with the swingarm/lower bars. LR upper - lower = more bite, higher = less bite (through the corner). RR upper lower = more rear steer, higher = less rear steer.

4) have not messed with bar length, so I'm sure someone else can clarify better.


for a starting point for you, if the car is tight and not rolling through the corner, take LR bar up, RR bar down. I like keeping rear steer in, and tightening up the car in other ways, but that's personal preference based on driver. I'd advise starting with RR bar down, and adjusting LR bar, and if you find you're still too loose, then take RR bar up.

[racin6mod]

the bar length affect the radius on which the bird cage indexes.in most cages you want 2 inches of differance in the lengths.but that has always been up for debeat and the lengths also control some of the rearsteer I once raced with a guy that ran his top bar(4 bar ls)shorter than the lower bar and that thing had a ton of rearsteer and lr hike but was all over the track.

on a z-link the spring does not have tobe on the axle tube it can be on the birdcage as well(most often on the lr) to me a z link with the springs mounted on the birdcages is basicly just like a 4 bar set up. the adjustment are the same you just lower the back of the top bar instead of raising the top bar in front on a 4 bar. just my oppinions

here a couple photos of the swingarm chassis the red one is a new rayburn notice the bar angles good starting point.the second is of my brother lm with a basic rayburn set up that hook up really well.

[SweetBabyJames]

Terrific. That was very helpful. Thank you for your feedback.

[dualdj1]

yeah sorry i should've clarified better, racin6 is correct z link can be either spring on a clamp on the axle or on the birdcage. However, z-links don't index like the 4 bars do. They will index some, but not as much, and sometimes in different direction than 4 bar depending on your bar settings.

[Dirtracer50]

Has anyone ever played around with mounting the springs to the swingarms and the shocks on the birdcages? Would you run them the same as a 4 link with LR shock behind and RR shock infront? Seems it would be easier to make shock changes just not sure what kind of effect it would have.

[racin6mod]

before they allowed coilover shocks that's how you had to run a swingarm .booth shocks behind the axle but thats mostly due to space.

[js11]

All great advice. Also, I've run this set up with 20" lowers and 15" lowers. The 20" lowers required more innitial angle on the LR for forward bite than a 15" lower. Shorter lowers = quicker drive. The uppers can be equal in length (making indexing and rear steer or non rear steer adjustments more predictable. A lot of guys like to run the upper LR bar longer (Rayburn set up, I think).

Shocks on the birdcage are a good way to go.

Note: this set up seems to like less angle on the j-bar and more spring on the RF corner to keep the car on the LR spring.

[car4cyl]

I just picked up a Champion Chassis with swingarms and Z links with the braks floating on the birdcages , What I need to know is what springs and shocks rates I should use???? also what is better coilover or springs on a slider?? Thanks

[racin6mod]

put the brake cal.on the axle tubes you want to run the braking energy through the chassis,run the rr with a coilover shock 93-5 and the lr with a slider on the swingarm and a gas 8-2 shock behind the axle this helps control the lr drop under braking.