Stephen Hales, 33, was competing in the Canterbury ATV Association's hill climb race in Ashley Forest on Saturday afternoon.
Police say he failed to negotiate a bend while racing downhill, hit a clay bank and was thrown from his bike.
Attempts to resuscitate him failed and he was pronounced dead at the scene.
The police say he had serious neck injuries.
Sergeant Brent Register says an investigation is underway. He also says the motorbike association gave a safety briefing before the competition began and that all safety rules were adhered to.