Senior Constable Jeff Cramp, a crash analyst for Northland police, said the inexperienced 19-year-old motorcyclist was on a Harley-Davidson which was deregistered and in disrepair.
It appeared he was following a carload of friends and family members when he failed to take a corner on the sealed road and crashed into a farm fence.
He suffered severe head injuries and died at the scene.
Speed was not thought to be a factor, though he may have been trying to keep up with the car, but inexperience almost certainly was.
He almost certainly would have survived had he been wearing a helmet, Cramp said.
In the earlier crash two unlicensed 16-year-old girls had been driving on the Waipapakauri Straight, on SH1 about 15km north of Awanui, when the driver attempted a passing manoeuvre but failed to see a car approaching from the other direction.
She swerved to avoid a head-on collision, rolled the car and crashed into a roadside drain.
Both girls were unrestrained. The driver, who was thrown from the vehicle as it rolled, suffered life-threatening injuries and was flown in a critical condition to Auckland Hospital by the Northland Rescue Helicopter.
She was still in intensive care yesterday morning but in a stable condition.
The car travelled about 50m from the initial point of impact in the drain to where it finally came to rest.
Cramp described the passenger as ''walking wounded'' with moderate injuries.
Both would likely have suffered only minor injuries if they had been wearing seatbelts, he said.
''Seatbelts and helmets save lives, there's no doubt about it,'' he said.
Just last month a 22-year-old man suffered critical head injuries while joyriding on a motorbike at Te Tii, north of Kerikeri, without a helmet.
He lost control on a corner and was thrown into a rock-filled drain.
He is, however, understood to be recovering.
The motorcyclist's death brings Northland's road toll for the year to date to 15, according to Ministry of Transport figures.
That is one more than at the same time last year despite the Covid-19 lockdown emptying the roads of traffic for five weeks.
Although both of Wednesday's serious crashes involved teenagers, Far North Reap road safety educator Jodi Betts said the group with the biggest increase in road fatalities was men aged 29-59.
That was why the latest Northland road safety campaign, called Think — One Tear Too Many, specifically targeted that group.
''It's not just young people. It's people not getting the basics right. Even before the lockdown guys weren't looking after themselves or thinking about keeping themselves and others on the roads safe,'' she said.
Some drivers were being caught out by the change from dry roads to wet, or were stressed and fatigued because they'd had to change shifts or take on extra work due to the Covid crisis.
''People are in quite a different headspace than before the lockdown. Some of the driving is diabolical, people are taking enormous risks.''
Since 2016 eight Northlanders aged 0-15 and six aged 16-19 have died in crashes. That compares with 11 aged 20-24, 16 aged 25-39, 27 aged 40-59 and 17 aged 60-plus.
