29er outside diameter on the 4" tires. Acts like suspension.....isn't as slow on pavement as you'd expect - not that I'd recommend a coast to coast road tour on those wheels.
I don't see myself building a touring bike with more than a 9spd cassette and one chain up front or an IGH [8 or 11spds]. That level of simplicity is more important than walking once in a while.
very neat, 4 inchers, wow. can see how they would be great for being on roads like and especially worse than the one in that shot of you. From the comfort side of things and the "float" aspect of them, for soft and/or wet stuff. What sort of psi do you run, lets say like in that photo--ie, load, road surface? 40 psi is my first guess?
As for the simplicity angle of not having a fd, I guess horses for courses. In rough stuff, mucky and all, I can definatley understand. As I understand, the IGHs are very well made and therefore gets rid of the maintenance issues of a rd also.
For the road touring Ive done, regular old fd and rd arent an issue, keep everything clean and lubed, they generally work.
With your terrain, the possibility of a fall and dings are going to be so much more possible, and damages with it, so I can see going simple.
But not for road touring, give me more gears and especially low ones and I am happy (me and my knees)
Oh, I can see however not wanting a front derailleur etc, as your spare tubes and fist size patches must weigh about 10 lbs so you have to take some lard off elsewhere ;-)