Originally Posted by
dddd
A split crown race seat never touches the balls or rollers, that would be a split crown race, which does not actually exist as a production item.
The split crown race seat is only ever a good idea if the seating area is tapered such that the cup or cartridge bearing itself positively prevents the fit on the steerer from opening up and presenting looseness. In that case, the split in the crown race seat can do no harm as the taper imparts an inward force all the way around the crown race seat, thus preventing any looseness from ever developing between the crown/steerer and the crown race seat.
The crown race seat is what the 26.5mm part of the fork is called though, and the conical thing that the bearing sits on will almost always be called a crown race by manufacturers, whether or not it's actually a race. If you had to come up with a technical name for it, it would be something like cartridge bearing crown race seat adapter.