In my experience it depends on the bike, the saddle, the ride and the rider. It is too cold here for me to ride regularly year round. In the early parts of my cycling season, I have to toughen my tuchus. Once I have that done, shorter 20 or so mile rides are fine in running shorts. Longer rides I like padded shorts.
I wish GPS would have been around in the late 70s because I'm pretty sure I rode more miles in cutoff jean shorts than I do now in lycra.
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"It is the unknown around the corner that turns my wheels." -- Heinz Stücke