About 2 degrees to 2 1/2 degrees positive caster should be sufficient, just enough to get a predictable return to center after a turn, and a stable straight-ahead track on a level road with an average drainage crown. On independent suspension systems, it's common to put in about 1/2 degree "caster stagger" where the left wheel is closer to zero caster than the right by a fraction of a degree. This compensates for drainage crown and allows a vehicle to track more or less "hands off" by leading slightly to left and "climb" the drainage crown. A straight axle would have to be twisted to get different caster side to side, something that I haven't seen done regularly since the late 1950's. I have seen an occasional bending of the end of an axle up or down to correct a camber problem, but putting a twist into the end of the axle is a lot more difficult than an up or down camber correction.
Jerry
Last edited by Hotrod Lincoln; 02/28/2015 10:12 PM.
