Originally Posted by markf
I seem to recall seeing on the Riv website that the smaller Atlantis frames will accept tires up to 26 x 2.125", this would translate to around a 700 x 53 for the larger frames that accept 700C tires. Fat tires like that could be a real good thing to have on the tour that the OP proposes.
The Surly's 54cm and smaller will accept tires 26 x 2.1" with or without fenders.
http://www.surlybikes.com/longhaul.html