Mr Brons climbed out of the Toyota Landcruiser and tied the end of the winch rope around his waist and attempted to walk across the river - which was swollen and fast-flowing due to recent heavy rain - to the opposite bank.
His close friend Ryan Dick, who was driving the 4WD, said both he and Mr Brons had successfully carried out such crossings before.
However, on this occasion Mr Brons was dragged downstream by the strong current until the 30m rope was taut.
He was held in position for around two to three minutes, and could be seen struggling to keep his head above water.
Mr Dick told the inquest he could see the top of Mr Brons' head in the water, and see that he wasn't moving.
The rope then snapped, and Mr Brons was swept downstream.
Police were notified, and a search and rescue operation found his body two days later around 1km downstream. The incident was captured on video footage.
Expert witness Dr Charmaine Tate said the rope tied around Mr Brons' waist would have hindered his attempts to survive.
If a person is immersed in swift water they should adopt a defensive swimming position, with their back to the flow with both feet pointed downstream, she said.
A rope should be held over their shoulder.
"Once Jeremy lost his footing, the presence of the rope around him pulling against the force of the river and his position facing upstream resulted in his face being forced under the surface," coroner JP Ryan said.
"Dr Tate considers this would have caused a relatively quick loss of consciousness as his airway was overwhelmed by water."
Four-wheel driving advocate Michael Sheppard, who gave evidence to the inquest about best practice, said the decision by Mr Dick to drive across the river appeared to have been a reasonable one under the circumstances, and given that Mr Dick had previous experience of crossing that river.
Mr Sheppard suggested a number of alternative options the group may have considered to free the vehicle before Mr Brons attempted such a crossing, but coroner Ryan said the potential effectiveness of any of those was "moot".
However, there was "considerable value" in four-wheel drive enthusiasts being aware of the variety of techniques available to them, he said.
"It is tempting to suggest that with the benefit of hindsight, the Upper Grey River was not safe to cross on September 27, 2014. However, it may be that it was simply bad luck that Ryan's truck became hung up on a boulder."
The trip was not part of an organised activity by a club, but "simply a collection of like-minded enthusiasts setting out on an expedition as a company for mutual support", coroner Ryan said.
"However, the events that unfolded on this expedition highlight the benefit of group members having some training in safe practices, particularly with regard river crossings.
"In giving his findings, coroner Ryan recommended four-wheel drivers join an official club and undertake training before attempting such river crossings.
"Given the inherent risk involved in driving four-wheel drive vehicles through a fast-flowing river, which is sometimes done by four-wheel driving enthusiasts, it would be prudent for such enthusiasts to undertake some raining in safe practices for river crossings," he said.
"I would therefore encourage all four-wheel driving enthusiasts to join a club which offers such training in a theoretical and practical setting."
