Asked to describe his feelings about high velocity after completing his 200/400m double at last year's Olympic Games, he likened it to his childhood experiences in a home-made go-kart.
Next week Johnson, who makes his first British appearance in five years tomorrow when he races at Crystal Palace, will take command of a far more powerful means of transport. He has been invited by Ferrari's Michael Schumacher to spend a day with the team before the Belgian Grand Prix, and offered the chance of getting behind the wheel of a Formula One car.
The prospect of athletics' hottest property careering round the Spa-Francorchamps circuit on four wheels can hardly be comforting for Johnson's agent, Brad Hunt.
But Hunt, who has guided Johnson's business career since he arrived on the international scene seven years ago, is sanguine about the runner's plans. He knows that Johnson is not likely to do anything silly.
"Control is a key word for him," he said. Johnson will set about driving in the same meticulous fashion in which he prepares for racing on the athletics track, applying power only where it is required.
It is a curiosity that Johnson, who pulled out of a planned appearance at Sheffield after his defeat in Paris, should be making his return to this country at 200 metres, the distance he refused to run in last year's British Grand Prix.
His plans to run the 400m there were frustrated by a desire on the part of some British officials to prevent home runners suffering what they feared would be a morale-sapping defeat on the eve of the Atlanta Games. "If I had been one of those runners, I would have felt the decision was disrespectful to me," Johnson said.
Johnson's handlers made it understood that he would never run in Britain while the British Athletic Federation's executive chairman, Peter Radford, remained. Radford's departure this year has opened the way again.
In the wake of his exploits in Atlanta, Johnson has found his life opening out. This year he has devoted much energy to establishing himself as a commentator and analyst for NBC television, for whom he worked during rounds when he retained his world 400m title in Athens this month.
On the track, too, this year, it has been a case of what he describes as stepping into the unknown. His experience in Toronto on 1 June, when he pulled up injured during his $1m (pounds 630,000) One-to-One 150m challenge with Donovan Bailey, disrupted his season.
He still, one suspects, carries a cold anger at the way in which Bailey and emboldened members of the Canadian press baited him after the race, calling him, in Bailey's words, "a faker and a chicken". Johnson is unwilling to be drawn into discussing the matter.
"It's over now," he said. "You put these things behind you and move on."
His injury, to a quadricep muscle, caused him to miss the US trials. But the offer of a wild card by the International Amateur Athletic Federation guaranteed the appearance at the World Championships of the man most capable of boosting US television ratings.
Before receiving that invitation, he had suffered his first defeat over 400m in eight years, when he finished fifth in his comeback race in Paris on 25 June. Apart from one minor outing in Houston, he was not able to race again before defending his title in Athens.
"This is a very different season from any other I've had," he said. "It has been difficult for me to put a finger on where I'm at at any particular point."
It is a fair bet, however, that Sunday's appearance in the Spar Challenge - his first 200m in Britain since his astonishing 19.85sec performance seven years ago on a cool evening in Edinburgh - will not cause him undue stress.
Johnson, who will be 30 next month, has learned how to stay the course over the last decade. It is a virtue he ascribes to only two other 400 metres runners - his American colleague, Butch Reynolds, and Britain's Roger Black.
Asked to evaluate the new generation of British one-lap runners - Iwan Thomas, Mark Richardson and Jamie Baulch - Johnson replied with characteristic caution.
"In Britain there is always someone who is running well, but the next year they are not there. Someone like Iwan Thomas has run good times, but you have got to be able to continue with the same type of form throughout a championship. As a competitor, I'm sure Iwan's not happy with what happened in Athens."
The reason for the high casualty rate in one-lap running, he believes, is inherent in the event. "It is very difficult to train for and to run, too," he said.
"A lot of guys don't really know what they are doing out there. You can get lucky for a while, but then you have to learn your event.
"It is more mental than a lot of people think. Nobody can run the 400 all out. You have to know the pace, know when to give full effort and when less than full. It's difficult for a lot of guys to understand that."
Even more difficult for them to do it in the way he can.
Bailey, Johnson's tormentor in Toronto, will also be running tomorrow in a 100m field that includes Britain's 19-year-old world junior record holder, Dwain Chambers.
Cathy Freeman, the first Aboriginal athlete to win a world title, runs the 400m, while Marius Corbett, the South African who was surprise winner of the world javelin title, meets Britain's silver medallist, Steve Backley.