Swingarm Roll Center

The first problem would be the solid rear axle because a double swing arm suspension would have the problem of the center to center distance would vary as the swing arms went through there travel in the up and down arc. Therefore if you are going to use a suspension with equal length swing arms then the axles must be able to to move in an arc equal to the swing arm arcs and the inner mount points of the swing arms must be in line with the pivot point of the half shaft if you are using convention u-joints on the axle. The mount points can be slightly offset if you are using CV joints as they have small amount of ability to extend and contract so that it gives an ability to fit the suspension to the vehicle. To be able to explain how to design and evaluate the geometry of automotive suspension system requires a desire to exert yourself to the studies of engineering or many years of study at the college of trial and error which can be extremely dangerous to the person who will test the suspension in real life and that is a thought that I wouldn't want to look in the mirror every morning and realize that the design didn't work and someone didn't go home. There are some software programs that will assist in the design of suspension systems but they are susceptible to that great computer term GIGO ( garbage in garbage out) so you must still have the background if you are wishing to design an all new type of suspension.

I guess my question was where the roll center would be for a trailing arm suspension carrying a beam axle as unsprung mass. This is a dependant suspension system with no camber change on suspension travel. I'm thinking that when looking at the car from the side, the roll center would be at the center of the axle. However, when looked at the car from the rear, I think the the roll center is infinitely away to the side of the car centerline. Could someone verify my thought process?

Thank you!!! That's very helpful. So for a single trailing arm, the side view gives the the instant center lying on the axis of the pivot center. When looked at from the rear of the car, it is theoretically at an infinite distance to the side of the car along that pivot axis since the suspension does not really "roll" because of its dependant nature. I hope I'm right.

No the actually the roll center is a finite point which will be at the center point of the suspension.and the rch is established by the planes of the links. Hope this helps clear things up but just remember and think of it as if you support the vehicle at the roll center then any action to one side will have the exact opposite affect on the opposite side

I think the FORMULA you need is the one described in the Ackerman principals

You might google that..Hope this helps you..

Those Pictures are great. It appears to me that the center-line of the axle is the roll point from the side as you said, and the center-line of the drive shaft/rear-end is the roll point for the lateral control.

IMHO.