With the adjustable factory type tapered roller bearings, when your moving the adjuster in or out to adjust preload on the bearings, your actually moving your axle flange in or out also.
The aftermarket disk setups use a fixed caliper, which you will shim as neccesary to get it centered on the disk when you mount it. With green bearings the axle flange and disk will always be in the same place.
When adjusting the tapered bearings, where you get the proper preload, may not be where the disk lines up with the caliper.
hope that makes sense.
Maybe someone else can explain it better.
