okay my understanding is this: there are certain "sympathetic" vibrations in the various suspension components that no amount of off car spin balancing can cure. the guys i used to go to, great little family shop, very, very contientious. (i moved, an advancement job wise) are a 100 miles away from me now
have this elecric motor on a small cart with a rubber wheel on the output shaft. they jack your car up at each corner, mark the tire with a tire marker as a point of reference, then spin the tire with the motor/wheel set-up. this is in conjunction with a strobe light, aimed at the tire sidewall, set up to correspond with the rotation of the tire. now from here on i never quite understood what they look for or how they do it, but from that point of reference mark, they determined the area where weight was needed (always on the inside of the wheel i may add) and that was basically it. actually was cheaper than a spin balance. i hope this helps a bit, do some calling and asking around you may find someone that does this, believe me it is worth it. before i had it done, the steering wheel in my XR4Ti bounced in my hand at any, yes any speed! afterwards smooth as a babies BE-hind!
