A little help? Modeling rear roll steer for 2 link

[exwestracer]

I started a new thread on this because it doesn't specifically relate to the torque arm suspension. I figured there might be a wider interest in this info, but one constraint will apply only to the torque arm.

Here's what I need help modeling: Roll steer (total axle length skew) for a 58" track width axle as lower link mounts move closer to axle C/L height. 3" up/down travel at end of axle (pure roll). Assume no influence from any other linkage. R/C centered in chassis and at axle C/L height. Links level, parallel to chassis C/L and 42" apart C to C. Rear link mount at axle C/L.

Case 1: Lower links 20" long and 5" below axle C/L height.
Case 2: 18" and 4" below.
Case 3: 15" and 3" below.
Case 4: (torque arm only) 12" and 0" below axle C/L height (front mount same distance from axle C/L as case 3, shorter links to accommodate mounting on front of axle tube).

What I am trying to figure out is how the roll steer will be affected by moving the links up while still maintaining reasonable frame construction/rear seat room.

Thanks in advance.

[Bryce]

Ray,

The closer the links are together the more radical the axle skew will be. Another advantage for making the LCA a wider mount.

In top view I dont think you will see much difference in axle skew when raising or lowering the LCA as long as it is horizontal and the same length. But when the links get shorter you will see faster changes.

I will draw this up in CAD on monday and run some kinematics.

[exwestracer]

Yeah, I picked 42 as kind of an "average" separation... Mine are closer to 48. I'm just looking for a trend if there is one. I may cut the lowers off the 51 and move them up to axle C/L height, but it will only leave me about a foot...
Thanks, Bryce.

[Bryce]

I started a new thread on this because it doesn't specifically relate to the torque arm suspension. I figured there might be a wider interest in this info, but one constraint will apply only to the torque arm.

Here's what I need help modeling: Roll steer (total axle length skew) for a 58" track width axle as lower link mounts move closer to axle C/L height. 3" up/down travel at end of axle (pure roll). Assume no influence from any other linkage. R/C centered in chassis and at axle C/L height. Links level, parallel to chassis C/L and 42" apart C to C. Rear link mount at axle C/L.

Case 1: Lower links 20" long and 5" below axle C/L height.
Case 2: 18" and 4" below.
Case 3: 15" and 3" below.
Case 4: (torque arm only) 12" and 0" below axle C/L height (front mount same distance from axle C/L as case 3, shorter links to accommodate mounting on front of axle tube).

What I am trying to figure out is how the roll steer will be affected by moving the links up while still maintaining reasonable frame construction/rear seat room.

Thanks in advance.

There is no change due to the link distance below the axle CL

I did some kinematics so keeping one link horizontal and moving the axle up 3" on the other side; these are the angles between the axle and the original axle vertical plane.

Case 1: .308*
Case 2: .343*
Case 3: .412*
Case 4: .518*

[exwestracer]

Would it be a whole lot harder to move both sides opposite one another? If the R/C is centered in the chassis, I'm thinking there should be some cancellation effect from both links changing angle...?

[Bryce]

Would it be a whole lot harder to move both sides opposite one another? If the R/C is centered in the chassis, I'm thinking there should be some cancellation effect from both links changing angle...?

Ray,

I was thinking about this more.... it should be the same moving one or both. The other thing is I did not model a panhard bar. I will model up a 40" long panhard bar that is horizontal at ride then move each end of the axle 3", one up and one down.

[exwestracer]

Bryce,
It seems that there should be a difference between keeping one link level, and having an equal but opposite angle change in both links...I think.:)