"It didn't bother me," Stewart told MTV News while promoting the film at the Toronto International Film Festival.
"You can do no wrong with [Salles]. He puts so much inside of you. In the four-week rehearsal process, it was OK to ask any question, to bring up any story, to really overanalyze everything and intellectualize everything."
By the time cameras rolled, Stewart said an errand like stripping down was "so not a big [deal]."
She said she welcomed the chance to do right by the book, adding, "Anything that feels guarded, in this particular movie especially, would just be so against the spirit of it."
"On the Road" costars Garrett Hedlund, Sam Riley, Kristen Dunst and Elizabeth Moss.