On the day of the crash Mr Rielly was driving south on State Highway 1 near Otaihanga, about 2.45pm, and began negotiating a sweeping right-hand bend.
He lost traction and moved across the centre line into the opposing traffic lane and crashing, Coroner Smith said.
"At that time the weather was poor and there had been consistent rain falling most of the day."
A witness to the crash said he believed Mr Rielly must have been passing another car and seemed to be travelling about 130km/h at the time and did not appear to slow for the corner before losing control.
"...it was in all likelihood that the speed was in excess of the critical curve speed in the conditions.
"The Honda was unable to negotiate the corner and stay safely in its vehicle lane."
There was no evidence of drugs or alcohol in Mr Rielly's system, he said.
Coroner Smith noted an earlier finding for Kelly Thompson, who died when her car also drifted across the centre line and collided with another in the same area, exactly two months earlier.
Since the crashes, the McKays to Peka Peka Expressway had been approved, which would bypass that section of road, Coroner Smith said.
In the five years preceding the crash that killed Ms Thompson, there had been nine crashes at the same spot.