To OP: If you have the old blue version of the FXE you can run up to 35c with some clearance for mud in the back. If you want a caliper rear brake you'll be able to fit 32c if you'll use longreach brakes.
I don't know the exact differences to the new ones but the old ones had longer chainstays than the equivelant pre cursa and also much more clearance. So much infact that it would be very troublesome to run a 42mm chainline with anything bigger than a 46T. Stupid design in that aspect.
To OP: If you have the old blue version of the FXE you can run up to 35c with some clearance for mud in the back. If you want a caliper rear brake you'll be able to fit 32c if you'll use longreach brakes.
I don't know the exact differences to the new ones but the old ones had longer chainstays than the equivelant pre cursa and also much more clearance. So much infact that it would be very troublesome to run a 42mm chainline with anything bigger than a 46T. Stupid design in that aspect.