Mr Gilbert told his wife to call an ambulance and ran down the hill to help.
"Honestly he's just gone a little wide on the corner [and slid on the slippery road shoulder]. I was just looking out and saw him go straight off the edge. People were there straight away helping. By the time I got [down my driveway] there were already four or five people helping," he said.
Murray Beerhe, also from Hamilton, had accompanied Mr Vincent to the car show in Tauranga, driving his own car.
He said he was driving ahead of Mr Vincent. But when he'd looked in his rear view mirror on Poripori Rd his friend was no longer behind him.
"I looked in my mirror and thought, 'Where the bloody hell is he.' It was just one of those things, he just went off the road a little bit and then he touched his brakes, which he probably shouldn't have," he said.
Mr Vincent was checked by Tauranga St John but did not suffer any injuries.
Traffic was diverted over the weekend as maintenance crews removed rocks from the cliffs above State Highway 29, at Ruahihi Bluffs, about 17km west of Tauranga near Ruahihi Power Station.