It is believed the 38-year-old lost control on a roundabout in the suburb of Redwood Park on Wednesday morning.
The force of the impact flung parts of the bike onto the other side of Milne Road.
His passenger, a 45-year-old man, suffered serious but non-life-threatening injuries.
The man was rushed to hospital just after 3am.
Emergency crews tried to revive Smith but he couldn’t be saved.
His former partner, Married at First Sight contestant Stacey Hampton, told 9News Smith “is now at peace with his brother, mother and friends”.
“He was an amazing father, he adored his children and his parents,” Hampton said.
“Our hearts are broken and our lives will never be the same.
“He had a heart of gold and adored his family and friends.”
His sister was among those laying flowers at the scene. Fellow Rebels took social media to pay tribute.
“Another brother taken too soon, you will be greatly missed and never forgotten,” one post read.
It follows the death of Rebels enforcer Bradley Daniele, who died suddenly in hospital last week.
Milne Road was closed for several hours on Wednesday morning as major crash investigators combed over the scene.
Redwood Park residents said the road was notorious for accidents and called for more to be done to improve its safety.
Smith is one of 52 people to lose their lives on South Australia’s roads so far this year.