He pulled over, went and said g'day, and experienced something of an awakening. "They were just normal, they spoke to me, and it was like, 'This is where I should be.' "

Shaw isn't the first young athlete to decide the sacrifices required to be truly elite aren't worth it. Yet it's not often the decision to walk away in search of normality is taken by someone who's already the best on the planet among his peers, and is tipped to not only make the transition from cycling's junior ranks into the Australian team for the 2016 Olympics, but hurtle around the Rio track so swiftly he would finish on the podium.

David Lunn, a former elite rider who has been a friend and mentor, notes, "It's everyone else who wanted that for him. Zac always says, 'It was never my dream, I just wanted to ride fast.' "

Cycling officials still hope he'll change his mind, have told him to take his break, rediscover the passion. The Rio door is open until October; they've told Shaw that three or four months of toil is all it would take to get him back up to world-class speed.

He appreciates all they've done for him, but isn't about to bring them good news. "I say I'm taking a break so as not to totally disappoint people," he says of what he tells anyone who asks, "but realistically I don't see myself riding again."

His 19th birthday on Wednesday underscored the life he's left behind, and the ordinariness of the one he's chosen. A year ago, he got his driver's licence the day he turned 18, drove through Melbourne's streets for the first time to the Darebin velodrome, donned his Victorian Institute of Sport jersey and got on his bike. If not this, he'd ride the bike paths from Ferntree Gully to VIS headquarters at Albert Park - "an hour and 10, or 45 minutes if I was running late and put the foot down" - before switching from commuter to athlete.

This week, his working day still began at 7am, but in a Colac timber mill where three months ago Shaw started a mobile plant mechanic's apprenticeship, "fixing stuff that's broken - loaders, forklifts, all sorts of vehicles". Before Shaw became a bike rider at 12, his grandfather gave him an old motorbike, and he discovered the joy of pulling things apart and putting them back together.

Now, his "training" entails being in his uncle's pit crew as he races super rods at speedway tracks from Avalon to Echuca. He's building his own car, modifying an old 302 Cleveland engine, which he aims to be racing within a year. "Going round in circles real quick - but with an engine instead of on a bike."

He hasn't ridden a bike for five months, and actually no longer has one to ride. After the junior worlds in Glasgow he sold one and bought a VZ Commodore. The other belonged to the VIS, and had been gathering dust in his Mum's garage until someone came and collected it last week. They wanted him to hang on to it just in case, "but I said 'No, don't waste a good bike, give it to someone else.' "

Glasgow 2013 was the proving ground for his uncommon talent. A year earlier, in New Zealand, Shaw had won the one-kilometre time trial. In Scotland he stepped out to the three-k individual pursuit, challenging himself to transfer from sprint to endurance on six months' training, against rivals who'd tackled the longer distance since they first sat in a saddle. "No one's ever done it - won the kilo and then the three k."

He'd always seen himself as an endurance rider, but switching virtually on fast forward took a toll. His parents separated, he felt mentally drained and almost came home from a two-month camp at the AIS in Adelaide. The size of the challenge dawned on him, and for the first time he questioned his own long-held theory on all things - "that I could just do it, full stop".

Cycling had always been fun; he liked the banter on long training rides, the culture at his local club, would turn up out of the blue and hold a flag on a corner at veterans races. He also discovered that he liked to compete, virtually toying with the competition at state titles, winning nationals on little training when few thought he could.

Lunn says his ability to push beyond where testing says his maximum oxygen consumption should be is extraordinary. Shaw says he can't remember much about racing, only that he would "dig down and bury myself", hurt like hell but drive himself on, thinking only, "breathe, ignore the pain ... how many laps have I got left?"

In Glasgow he defied the odds by winning the individual pursuit, then tried to defend his one k title. He finished third, a whisker off winning, and collapsed in a screaming heap. It was half an hour before he could even summon the strength to sit in a chair.

"I think that's what made me strong - I could find that extra bit where I'd spew for half an hour afterwards, push myself so hard that I'd get a headache and not be able to see properly. I could push myself through the threshold and into that extra red zone."

It's this cocktail of raw talent, will to win no matter the physical cost, and outright mongrel from gun to finish line that makes coaches salivate in any athlete. Shaw understands that people are disappointed with his decision, but can't abide the reaction of some.

"People say, 'What a waste of talent', straight to your face. I can't understand that - I'm doing what I want, I'm happy, leave it be.

"You could be monumentally awesome at netball and still not want to live it. Do you see yourself doing that every day for seven hours? That's my point exactly."

Phil Anderson, the legendary Australian road racer, spent time in the Colac area and knows Shaw as a focused young rider who "did everything he could for the sport". He would be disappointed to see him walk away, given the long odds that he'll come back, but acknowledges the huge sacrifices he's already made, not least leaving school in Year 10.

"He's got all these fantastic results, all the accolades, but obviously he feels he's missing out on other things," Anderson says. "He could just be fed up. They get dragged around the place ... looking over the fence at their mates can be pretty hard."

Shaw reflects that something he viewed as a hobby became a job, and he realised he'd never thought of cycling that way. For all his talent, he knows there are no guarantees, yet couldn't contemplate "years of maybes or coulds, I wanted it confirmed".

Last Sunday night he watched the Paris-Roubaix, went to bed, and realised he hadn't for a single moment thought, "that's awesome". His world championship gold medals are under his bed, his jerseys in a cupboard; the wall of trophies won throughout his teens will soon come down and be packed away too.

He still goes to the gym three times a week, "just for myself", and rejoices in the simple pleasure of exercise. As a cyclist he wasn't allowed to swim; "having only 4.1 per cent body fat meant I'd sink". Jogging was off limits too, but this week he ran 10 kilometres. "I just went for a run."

Now, he goes to "parma night" with those mates he didn't see for so long, tinkers with his car, pulls things apart and puts them back together again, embraces his apprenticeship. He catches up for coffee with Lunn, and smiles to think his friend recently told him he'd never seen him look so happy. "I'm back where I was before I started."

If, in a couple of years, he thinks he's made a stupid mistake, he believes he'll still be young enough to get back on the bike. Asked if he's proud of what he did, Shaw replies: "I don't really think about it. It was good at the time."

And Rio? "It doesn't matter at all. I'd rather just go to work."