With the cycling season kicking into high gear, the strongest doping allegations yet against Lance Armstrong surfaced Thursday in a barrage of detailed messages from Floyd Landis, the disgraced rider and former teammate who finally confessed to years of cheating himself.

In a series of e-mails sent to sponsors and sports officials, Landis alleged Armstrong not only joined him in doping but taught others how to beat the system and paid the former president of the International Cycling Union to keep a failed test quiet.

“We have nothing to hide,” Armstrong said at an impromptu news conference before the fifth stage of the Tour of California.

“Credibility,” the seven-time Tour de France winner said in Visalia. “Floyd lost his credibility a long time ago.”

In two e-mails obtained by The Associated Press, Landis also admitted for the first time what had long been suspected — that he was guilty of doping for several years before being stripped of his 2006 Tour de France title.