Having ridden a friends S fatty with 4.5 I have some time on a fatty and amazingly fun. I feel a 3.8 is the perfect modern day fatty tire size only because i have 3s on my plus hardtail. We got back to a article recently on tires. This time of year in north east states is ridable with a fatty or plus to be enjoyable. Sloppy snow ,rain, frozen, thawing conditions make it a mess but thats not to say you cant have fun. Ultimately I would like to add a true fatty that can handle 4.5s but feel a 3.8 is is a good cross between a 2.8 and lets say a 5 as we know real enthusiast run big baloonies