Dozens of journalists were in attendance at a supermarket car park in southern France ahead of the 43-year-old's ride to Rodez, but no fans were there to greet the Texan.
Armstrong is taking part in Geoff Thomas's 'One Day Ahead' charity event.
The American joins former England footballer Thomas and a team of amateurs, who are aiming to raise $2 million for Cure Leukaemia by cycling the route of two stages a day before the official peloton passes through.
Asked what kind of reception he was expecting from French fans, Armstrong said: "I don't know... all I know is this is a frenzy. But if I compare this experience to going to dinner in Toulouse last night with local people, it's very different.
"People are always very nice, I respect it and I appreciate that and I enjoy being here."
While Armstrong is riding to Rodez, the Tour de France peloton will embark on a punishing mountain stage that culminates with a climb up to the Plateau de Beille.
Chris Froome (Sky) leads after 11 of the 21 stages, the 2013 winner almost three minutes clear of nearest challenger Tejay van Garderen (BMC).