A young driver reached speeds up to 160kmh with one hand on the steering wheel as he swerved along a windy Hawke's Bay road.
Shortly after, Dwayne Bryce Fryer's car left the road, tumbled for 10 metres, then finally came to rest on its roof 300m from where it left the road. Fryer, 16, was dead inside.
Coroner Christopher Devonport has released his findings into the September 23, 2013 crash on Ongaonga Rd, Waipawa.
He found the cause of death was a head injury caused when Fryer lost control, ''with the vehicle sliding backwards off the road through a farm fence and tumbling 10m into a gully before crashing through another farm fence and coming to rest on its roof in a paddock''.
Fryer's passenger, Dayton Aramoana-Clarke, 18, survived.
He told Devonport that Fryer had just his right hand on the steering wheel as he reached speeds of between 140kmh and 160kmh before the crash.
''Mr Fryer was reaching across his right arm with his left arm to flick cigarette ash out the open driver's side window and each time he did so the vehicle veered slightly over the centre line,'' the Coroner's finding said.
He was accelerating, swaying the steering wheel, causing the car to sway within its lane.
Aramoana-Clarke remembered the car hitting gravel, swerving, then sliding.
Bailey Froggett, 17, who was driving a car behind, estimated the car was travelling at 120kmh when it left the road.
''He had thought that the way Mr Fryer was driving around the corners and driving on the wrong side of the road on blind corners that something was going to go wrong.''
Froggett and his two passengers all reported seeing sparks coming from Fryer's car, which a police officer in a serious crash report put down to the cigarette ash being flicked out the window.
The same report - which found nothing on the car that could have caused the sparks - found the cause of the crash was high speed on a windy road, mixed with inexperience, and over confidence.
The unsafe driving - having one hand on the steering wheel - also played a part, police said.
- The Dominion Post