The width of the road varied by almost 1m in the northbound lane, meaning it would be "virtually impossible" for any motorist to gauge the distance to overtake any cyclist.
Taupo District Council has since reviewed lane widths and widened or resurfaced some areas.
The group Mrs Farrelly was with had originally planned to cycle a 92km Girls on Bikes event in the area, and continued on with their plans when the event was cancelled.
Each member of the group was an experienced cyclist and they were riding in single file at the time of the crash, the coroner found.
Evidence from cyclist Yolande Savage at the inquest detailed the moment she watched Mrs Farrelly get hit.
"I was behind Jane ... I was looking ahead watching Jane's wheel as I was a couple of metres behind her. She stood up on her right pedal and turned around to look behind her.
"I saw her wobble and as the truck hit her hand went up in front of her. I did not hear the truck coming from behind at all so I got a shock when I heard the brakes screeching and a thud as he hit Jane," she said.
The cyclists were all startled by the truck as it overtook them, Mr Matenga found.
"No one in the group of cyclists heard the truck approaching until it began to pass them. The truck came as a complete surprise," he said.
Truck driver Larry Boulcott told the inquest in 2014 he hadn't had an eye examination in at least five years at the time of the accident. He later had a test which found he required specialist glasses.
But Mr Matenga found the truck driver's eyesight did not cause the crash.
He said he was not able to consider whether one eye test for truck drivers every 10 years was insufficient because of the finding.
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