there was a change from 99 to 2000. i believe in 2000 they went to a narrower belt. i just checked my 99 fxdx and do not see the room to go to a 150, however i have been running a 140 alternately with metzler 880 and a avon vennom. they clear and work fine. i just went back to the 880, i found the vennom to hard a compound for my style of riding. nor. cal rural and lots of twisties. [ just the way i like it].