-
I am not going below 2'' for sure, currently still torn between Kona Sutra (could bring 2.2 MTB tyres, 2.15 Almotions, or 27.5x2.6) or Genesis Longitude. 27.5+ setups look appealing for dirt roads, wondering though if scarce spares availability might be a problem in case my wheel brakes, and if those setups won't be too draggy on the roads (though Alee's setup with 2.4 slicks seems especially interesting to me).
It really depends on the route.
Even the Carrettera Austral has some bits on thick loose gravel that require 2" for comfort riding. If you go in the open flats of the Ruta 40 or even the big plateus of Bolivia and the coast of Peru then expect a lot of wind, for which I'd rather have a wide drop bar with a good flare.
If you then follow some of the routes that Ryan Wilson or Alee Denham then I'd bring a MTB rig with 2.4"-2.6".
The best thing is not to overthink it, you will manage it and have an awesome time regardless of what gear you go with. Just make sure it's reliable.