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Looking to mount on a stock rim size says 2.15 in the WS manual, but it is 3" on the bike outside to outside ? I really have no idea so I hope someone knows whats what.

Yeah i saw that thats where i got the idea from :-) still I would like to hear someone tell me its doable

OK plan B, I know a guy with a stock fatbob rim (19" I believe) could I mount this up in my stock setup?

Have just done something similar to my 04 WG, but went all the way to a 16" rim.  Picked up a stock 16x3 rim from a local shop, stainless spokes from Rollies for $150. Had it laced to my existing WG hub.  It's dropped the front 0.95", which matches the 1" drop I have on the rear.

Anything is possible...... its only money

dc