Judge Bruce Davidson said that Hiroki exhibited an extremely bad piece of driving that day.
"It must be extremely dangerous to drive a motorcycle directly at oncoming traffic on the incorrect side of the road with a 100km/h speed limit," he said.
"You held your line, described by one witness as playing chicken. You caused the driver of the utility to veer left. The utility and trailer then lost control."
Hiroki faced three charges of driving dangerously causing injury, two charges of failing to stop or ascertain injury, driving in a dangerous manner, possessing an offensive weapon and driving dangerously causing death.
Judge Davidson found him guilty of all charges on February 8 following judge alone trial and Leask was found guilty of driving dangerously and failing to stop or ascertain injury.
Leask was sentenced to five months' community detention and nine months' supervision. He was also disqualified from driving for 15 months.
An earlier collision of vehicles on the day Nelson died was said to be a contributing factor in how Hiroki was driving dangerously.
Crown witness Erica Bak testified in court on January 29, describing an incident close to Bulli Point near Taupo where she rounded a bend to find a motorcycle on her side of the road.
"It was going to hit me fair and square in the middle of my bonnet, so I took evasive action. I moved as far to the left as I possibly could without going into the lake," she said.
"He came right down the side of my car. His foot peg punched out my tyre. In my side mirror I watched him thinking he was going to fall off, but he wobbled and fishtailed and drove off."
The driver was Hiroki, who stopped further down the road after the collision had occurred, took off his shoe and threw it away. His ankle had been fractured.
During the trial, Crown Prosecutor Chris Wilkinson-Smith submitted this alone was dangerous driving.
Many people were affected by the crash near Ohingaiti, including a young couple who were in the utility vehicle who were cut, bruised and needed time off work.
"Their relationship became strained with the male blaming himself for what had occurred and withdrawing emotionally from his partner," Judge Davidson said.
"This accident was not his fault and his actions immediately afterwards in saving himself and his partner, can only be labelled as courageous."
The ute burst into flames after rolling following the collision and a man driving another southbound vehicle was also injured after crashing into the trailer.
Judge Davidson said that Nelson's wife was devastated by his death.
"She has suffered significantly, emotionally, psychologically and financially," he said.
"I am told there has been support offered to her by others within your gang. She wants you to accept accountability for what occurred and demonstrate some remorse."
In sentencing Hiroki, Judge Davidson took into account what little remorse he had shown, but also his 30 year history of offending, including 40 driving convictions.
While on bail following the crash, Hiroki spat at a police officer and police discovered 21 cannabis plants and 104 grams of dried cannabis, worth close to $10,000, at his home.
He was further charged with cultivating cannabis, possessing cannabis for supply and assault.
Hiroki was sentenced to 4-1/2 years' imprisonment for his driving offending and six months' imprisonment for the drug offending. He was disqualified from driving for five years.
"In an inescapable feature of the case that needs to be confronted is that the deceased had driven badly that day as well, although probably not as badly as both of you," Judge Davidson said.
"Over several hours that day he took significant risks and sadly paid the ultimate price."
