The wheel was one of two that broke loose from the 10-wheel truck as it travelled at what police believe was excessive speed down Thepkasattri Road, Phuket's main north south artery.
Alexey Balabko, 26, was knocked out by one of the wheels as it crossed the median strip and collided with his motorcycle.
A second wheel crashed into a pickup, like Mr Balabko heading north from Phuket City towards the Sarasin Bridge.
The crash occurred in Phuket's Srisoonthorn district about 2.30pm. Mr Balabko remained in a coma today.