40 miles a day will not be a problem- some of us do that on their daily commutes- but the problem will be the Butt.
Get plenty of longer time rides in and give the butt enough time to get attuned to the saddle- and to get it set up right. I think most newcomers will be able to do 40 miles in a day after a few months- but to get on the saddle on the 2nd and subsequent days could be a bit painfull.
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How long was I in the army? Five foot seven.
Spike Milligan