Adjustable rear trailing arms and caster.

[Captain Snooze]

I can't seem to find any wheel alignment specs that mention rear caster. I don't know how one would even measure rear caster. I have fitted new rear trailing arms. How do I find out what the correct length is for the trailing arms given I don't have the oem arms to compare? Does it even matter providing both arms are the same length?

[Gforce]

Caster is another description of hub pivot inclination, fore and aft. That is described by the vertical line drawn through the upper and lower "ball joints" on double A arm suspension. For multi link it can be hard to determine exactly where the lower pivot point is. I like this link as a show and tell for the suspension geometry, scroll down to the rear suspension.

https://www.edmunds.com/car-reviews/...alkaround.html

Caster is not relevant for non pivoting wheels but the geometry of the connected links is critical. The rear hub caster angle changes with suspension movement so it is the relative arcs that matter. If the trailing arm is longer or shorter than stock then the toe link effective length will be different from stock and deliver different toe rate changes from stock. If you know what you want in that regard you can play with the trailing arm length and an alignment machine if you want to see how it works.

Since the toe link length is connected to both the trailing link and lower control arm through the hub and that length determines the toe setting throughout the suspension arcs you should ensure your new trailing links are the same length as stock. The straight line length from the mounting bolt to the hub bolt is all that matters. Any curves or drops in the arm itself do not affect geometry. Just measure your old ones bolt to bolt and adjust the new ones to the same length, bolt to bolt. Sorry, you don't have your old ones so you'll need to get under a stock car or ask someone to measure theirs for you.

There will be a very slight change in anti squat effect from different length trailing arms also as the arc of the trailing arm influences anti squat angles.