“Naturally, your riding style, comfort level, and how much weight you plan to carry will determine the answer to this for you. I rode it on a 27.5+ hardtail with a 120mm fork the first time around. The second time was on a Salsa Cutthroat with a Lauf fork and 2.1” mountain bike tires. I would not suggest anything smaller than a 2.1″ tire with great sidewall protection. I would also highly suggest front suspension with the ability to lock out the fork for the flat sections.
There are long stretches of beautiful gravel where a gravel bike would be ideal. It’s the mountain passes and the sandy stretches of two track that make a gravel bike unrealistic. Think about a Tour Divide rig and go from there. The more weight you plan to carry the more volume tire you will want.
[As for tires . . .]
I, personally, would not go smaller than a 2.1″ tire. Fast rolling with great sidewall protection and knobby enough for chunky rock and deep sand.”
Posted by Jan Bennett on Bike the Pony Express, 3/10/20