Its all about what your using the car for, the 20 degree users are mostly race cars and its done for stability but they quite often get the death wobble when coming out of the burnout.
On a street car i like 7 degrees, gives good straightline stability and the steering won't be to heavy.


Quote Originally Posted by J. Robinson View Post
Whenever I've tried setting caster at more than about 7 degrees on a beam axle (on my coupe, on 2 previous C-Cabs, and a T-bucket) the front end always shook uncontrolably, so I always shoot for 5 or 6 degrees. Yet, old rail dragsters had caster angles of 20 degrees or more... Can anybody explain how/ why that works on some cars and not others?