Gucci Mane is a Cyclist now!

He ditched the drugs ... he ditched the lean ... and now Gucci Mane is 'bout a different kind of life -- CYCLING!

The 36-year-old rap superstar has picked up the sport as part of his new, healthy lifestyle -- and he's even got the Lance Armstrong-style outfit to match.

Gucci famously battled with weed and sizzurp before he went to prison -- and now that he's out, he's vowed to stay clean.

Today is day one with the bike ... and he doesn't look half bad.