Against a year ago, light truck sales for the quarter to September were up 0.7% to 3674, medium-weight truck sales were down 9.2% to 218 and heavy truck sales rose 111.3% to 223.
Infometrics economist Mieke Welvaert said new very heavy commercial vehicle sales outpaced the growth Infometrics forecast for the September quarter.
First-time registrations were up 11% from last year, compared with the the 5% growth forecast, she said.
"High export volumes have helped keep a floor under heavy commercial vehicle sales," Ms Welvaert said.
Underpinning export growth was a favourable exchange rate, with the New Zealand dollar at two and a-half year lows against its United States counterpart this week and strong export commodity prices.
September commodity prices were at their highest level since 2014; in New Zealand dollar terms.
"With exporters increasing production volumes to make the most of current prices, we’ll be revising our heavy commercial vehicle forecasts upwards," she said.
New light commercial sales were only 0.3% higher than a year ago, but may have been caught up in the biosecurity scare earlier in the year, she said.
Stink bugs were discovered in three Japanese car shipments earlier this year and ordered out of New Zealand, which created a large backlog of vehicles awaiting clearance.
