Now, the tradeoff here is that a 4" tire on a ~80mm rim is about the limit for tire clearance, but that's ok if the alternative is horrible knee pain and no fun on your fatbike. 4" tires are damn fun, kids, even if the cool guys all have 5" ones now and look like babies waddling with full diapers on their ICTs.
I kid, I kid. Few pictures, geometry update in a minute.
-69 degree head tube angle, 45mm offset fork, and around 90mm of trail
-695mm front center
-310mm BB height (obviously depends on tire/inflation, though)
-435mm chainstay length
-83mm BB shell for happy knees and low Q
-170mm rear spacing
-150x15 spaced/Bluto swappable 480mm rigid fork.
-About 115mm of tire clearance at 345mm from the rear axle - this means basically any 3.8/4" tire will fit on 65-80mm rims. Bigger tires (or rims) are probably a no-go, though. 29+ and (more logically for BB height reasons) 27.5" will both fit with gobs of room.
|Lots of bending. Damn, the only straight tube is the head tube...and fork blades, I guess.|