The 20-year-old driver was uninjured.
Mr Pinker was one of a group of off-road enthusiasts who were riding motorcycles and the four-wheel beach buggy on the north bank of the Waimakariri River, approximately 3km west of the State Highway 1 motorway bridge.
Sergeant Mike Brooklands of Kaiapoi police said it appeared crash helmets were being worn by both men but it was unclear if Mr Pinker had been wearing a seatbelt.
"Seat belts were available," he said.
"We understand the driver was wearing a seat belt but have yet to establish whether the deceased was wearing one."
Alcohol was not believed to be a factor.
Police enquiries, including a serious crash unit investigation, are continuing and the driver of the vehicle has been spoken to.
No decision had been made yet on whether any charges would be laid, police said.
A post-mortem examination is being held today before the matter is referred to the coroner.
Any other recreational off-road vehicle users who may have been in the area and seen the beach buggy being driven have been asked to contact Constable Brendan Riley at Kaiapoi police on 03 371 8048.