Depends on whether you have manual or power steering, and small or larger tires.
You can get away with 1.5 to 2.5 degrees positive caster with modest sized tires and minimal change in backspacing with manual steering. Once you go over 3° with manual steering, you may start to work on your Popeye forearms.
Especially with larger tires or more negative offset of the wheels.
With power steering you can easily run 4 to 6 degrees positive caster like the full-size rigs were spec'ed out at from the factory. Some of the members here have even built 8 to 10 degrees into their rigs to promote return-to-center and good feel with their larger tires. Not sure how it's worked out overall, but I think I remember a few saying they were pretty happy with the results.
In case you're not aware already, lifting your suspension changes the caster angle to the negative, which is not desirable. So more lift equals worse manners.
Changing the caster is most easily done with offset C-bushings, but that negatively effects the pinion angle. More positive caster equals a lower pinion angle and possible vibration.
So the only way to get the best of both worlds for those that really modify their rigs is to align the pinion correctly for their lift, using the proper C-bushings, then correct caster angle by cutting the steering yokes off the ends of the axle tubes and re-orienting them before welding them back on.
More work, but you get the most for your effort.
So, basic and easy caster changes, for modestly built rigs, are made with C-bushings offset up to 7° and/or eccentric upper ball-joint collars with offsets up to 1.5°.
I always get the collars with the most offset available and anything that's not used to change caster can be used to modify your camber as well. And besides, most of us need the most caster change we can get!
Best bet, if you haven't already, is to take the rig to an alignment shop that can give you a readout (printout is best) that shows your current caster and camber readings. That way you know where to start right from the get-go and can make the best decisions.
That generic enough for ya?
Hope it helps some.
Paul
