Armstrong has confessed to doping during all seven of his Tour wins from 1999-2005, but insisted he raced clean when he made his comeback in 2009.
Wiggins, the current Tour champion, finished fourth behind Armstrong in '09 and bases his suspicions on observations he made while racing alongside the American in key mountain stages.
"I can still remember going toe to toe with him, watching the man I saw on the top of Verbier in 2009 to the man I saw on the top of Ventoux a week later when we were in doping control together," said Wiggins, speaking at a Team Sky training camp in Mallorca.
"It wasn't the same bike rider. You only have to watch the videos of how the guy was riding. I don't believe anything that comes out of his mouth anymore."
Sitting with his 7-year-old son, Wiggins watched Armstrong end years of denials by confessing to doping during a lengthy interview with Oprah Winfrey last week.
Wiggins said he experienced a range of emotions - from sadness to anger and finally to satisfaction.
"I had to explain it to my son because (Armstrong) had won the same race his dad had won," Wiggins said. "But by the end of the hour and a half, I had the best feeling in the world.
"When he started welling up about his 13-year-old son, and him asking what's all this about. I never have to have that conversation with my own son. His father's won the Tour clean and there's this element of being quite smug about the whole thing."
(Copyright 2013 by The Associated Press. All Rights Reserved.)