It's most likely something like a Two Knives DX-3000, or some other similar model from Two Knives... as that's what Micargi specs for most of it's fat-tire bikes.

A quick check with Vernier calipers with the tire partially or fully removed from the rim will probably yield a width suitable for a 1.5" and even 1.25" slick or semi-slick urban tire. 1.5" with about 10psi more than suggested on the tire sidewall should keep you rolling along just fine and with a lot less effort than your stock 2.0" tires.

However, do yourself a favor before RAGBRAI and have a bike shop inspect the wheels for proper and even spoke tension. That's one of the potential soft-spots with mass-produced wheelsets like the ones used by Micargi. You certainly don't want to start breaking spokes on the ride.