Its a large bearing that needs to have the hub pressed in/out and the bearing itself needs to be pressed in/out. I beleive the "rotor" looking bearing is a front wheel bearing.
They aren't too pricey from BMW, or pelican etc... I wouldn't buy an ebay bearing.
http://www.pelicanparts.com/bmw/cata...SUSaxl_pg3.htm Writeup for the E30...which is pretty much the same as the ti.
http://www.teamdfl.com/bmw/e30/rear_...ngs/index.html