He struck the barrier head and back first, with his legs in the air, some 73 metres from where the bike left the track. The force of the impact shattered his helmet.
The rider following Jones told the inquest the teenager had braked too late for the corner and his rear wheel had locked up. Jones released the brake, but his bike still left the track.
Jones braked again on the grass, but was "thrown from the bike violently". He all but cleared the gravel trap before slamming into the tyre wall.
Coroner McElrea found the likely cause of the crash was loss of control due to a temporary front brake failure.
He made a number of safety recommendations to the South Canterbury Motorcycle Club, which organised the event, and the South Canterbury Car Club, which owns the raceway.
Coroner McElrea urged them to consider air fences rather than tyre barriers on the corner where the crash occurred, when the track is being used for bike racing.
Air fences could be hired for more than $10,000 an event - an amount which Jones' father commented was far less than the cost of intensive care for his son.
Coroner McElrea also recommended the clubs ensure the gravel trap was adequately maintained and checked, and consider measures to make the grass less slippery, such as removing moisture.
He made the same recommendations, on a broader basis, to national body Motorcycling NZ.
Coroners have also ruled on the deaths of two men in separate South Island road crashes.
Christchurch man Matthew Barnes, 25, died in hospital of serious head injuries after a head-on crash with another car at Arthur's Pass on April 15, 2012.
He had been drinking heavily the night before, and flatmates - one of whom said he looked "really tired" - had urged him not to drive to Motueka.
Coroner McElrea found Mr Barnes' vehicle had crossed the centre-line before the crash. He was in excess of the legal blood alcohol limit of 80mg/100ml, with a hospital test showing he had 104mg/100ml.
Marlborough man Timothy Shand, 63, died when his Nissan 4x4 left the narrow, unsealed Port Ligar Rd near his home on February 18 last year.
Coroner Ian Smith found Mr Shand had been passing a council tractor and mower, which had pulled over to the side of the road, when the right wheels of his Nissan went off the edge of the road.
He was thrown from the vehicle as it rolled 140 metres down a steep bank before coming to rest in a stand of trees.
Reports by police and council said the road was challenging, but noted both drivers were familiar with it. Coroner Smith made no recommendations.
