To ensure this is said as well - the bike is a pretty much stock complete Surly Disk Trucker, 2014 model year. The Bottom Bracket, however, is NOT stock. It is a Phil Wood that is several mm wider than the original.
The 4th chain ring is on a Mountain Tamer Triple adapter - essentially an adapter that lets you put a cassette cog on the crank. I think the one that is on there now is about 20t. I had a 17t on there originally, however it was stupid low. Ive managed to flip backwards climbing a hill with rear panniers and no front panniers with the ~20t ring so I dont think there is any merit to getting any more torque to the rear wheel anyhow.
With the stock bottom bracket you are supposed to use spacers on the drive side to push the whole mess out a few mm. I did that for a while but wasnt happy with it so I upgraded the bb to a wider one that put the chain rings at the position I wanted with a symmetrical alignment of tje crank arms on the centerline of the bike (not offset to one side as the original spacer set up was when the Mountain Tamer Triple first went on).
As mentioned in my first post - there are 0 mods to the FD. Only adjustments including the stop screw to widen the throw.