My understanding is the 999 has a 6 inch rim and has to have the 190, all the other bikes run a 180 rear. As Tim says the 180 on the 916/996/998 rears is a must unless it has a 6 inch rim.
dave
neither bike turns like a modern japanese in line 4 but most people adapt quite quickly
[Edited on 9-2-2005 by DAVE HARRIS]