When Michael Schumacher flicks his Ferrari into first gear and screams away from the grid, it will be the final grand prix start of his career.

Ninety minutes later, the most successful Formula One career will officially be over.

Schumacher will have retired.

The debate, though, will go on: the most successful, yes, but is Schumacher the greatest?

Greater than five-time world champion Juan Manuel Fangio? Greater than threetime world champion Jackie Stewart? Greater than Jim Clark, Ayrton Senna, Alain Prost or Niki Lauda? The reality is that such comparisons are impossible.

Schumacher has built the impregnable Ferrari machine around him since he moved to the Maranello giant in 1996.

Bankrolled by the biggest investment to date in F1 as the Italian firm strived to win their first world championship after 21 barren years, anything Schumacher desired he received.

He had the talent and the pace, but with Ferrari he also enjoyed a level of support, commitment, desire and development never seen before in Formula One.

But let's not belittle his achievements. The man has rewritten every record in the book: seven world titles, and possibly an eighth depending on events today at Sao Paulo; the longest reigning world champion . . . four years, 11 months and 17 days between October 8, 2000 and September 25, 2005; the most grand prix victories (91); most pole positions (69); most wins in a single season (13, 2004);

most successive wins in a season (seven, 2004) and most points (1,364). The list goes on.

But while Clark was racing opponents in the mid1960s in a car almost identical to those around him, and Fangio racked up his five world championships with a plethora of different teams, Schumacher's stats don't quite have the same sense of achievement about them.

That he has long been in a position of superiority, first with the excellent team of Ross Brawn and Rory Byrne at Benetton, and then at Ferrari when they followed him to Italy perhaps adds to the disappointment with his attitude to the spirit of his sport and his fellow competitors.

And it's that sneering contempt for his rivals which grates with those who are not Schumacher fans.

Talented, he unquestionably is. And there are countless examples of dazzling performances where he has extracted results which to lesser mortals would not have been possible.

Take the Spanish Grand Prix on May 29, 1994. Despite completing most of the race stuck in fifth gear, Schumacher managed to come home second, just 24 seconds behind Damon Hill.

He started from pole but began to suffer problems with his gearbox before the first round of pitstops during which he managed to complete his stop, stuck in fifth, without stalling the car and without losing the lead. Hill and Mika Hakkinen, who later went out with an engine failure, managed to make it past but Schumacher made his second stop, again without problems, and nursed the car home to a podium finish. Brilliant.

Perhaps the best though was the Hungarian Grand Prix on August 16, 1998. Traditionally a two-stop race, Schumacher and his Ferrari team rewrote the manual when, soon after the start and unable to eat into Hakkinen's lead, they switched from a two-stop to three-stop strategy.

"You have 22 laps to make up 18 seconds, " Brawn told his driver through the pit-tocar radio. "Okay, " came the reply.

What followed was a breathtaking sequence of 20odd metronomic laps at qualifying speed which guaranteed him the time for the extra stop. It had seemed impossible, but Schumacher emerged from his final pitstop five seconds ahead of David Coulthard's McLaren.

"We're in shock, " was all the stunned Scot could say afterwards. "You just can't win with three stops." While the rest of the paddock scratched their heads in disbelief, making the impossible possible had become an everyday occurrence for the German.

But that talent has always been tarnished by those moments when Schumacher's brain slipped into neutral and he has carried out the most outrageous acts of villainy which will be laid alongside his more illustrious achievements for ever more.

Those moments when he lost the ability to understand the distinction of where the line is and when not to cross it.

Adelaide in 1994. Locked in a world championship shoot-out with Damon Hill, Schumacher led from the start and had established a small but comfortable gap when he inexplicably pushed too hard, understeered wide and clattered a wall, terminally damaging the suspension of his Benetton. Crawling back to the pits, as Hill made a rash move to overtake, Schumacher blatantly turned in on the Williams, ending the Englishman's race. The title was Schumacher's. Controversially he went unpunished by the sport's governing body, the FIA, a trend which continued through his career.

Three years later at Jerez, Schumacher tried to take out the Williams of Jacques Villeneuve in the season's final race, which would decide the championship. This time, and thankfully for the sake of the sport, his Ferrari ended up in the gravel. Title to the Canadian.

Nine years on, we all thought Schumacher . . . who now regrets the move on Hill . . . had matured.

That, though, went out the window when he parked his Ferrari at Rascasse during qualifying for this year's Monaco Grand Prix thus halting arch rival Fernando Alonso's flying lap.

The hostile reaction, not just from F1 fans but, more tellingly, from the F1 paddock, stunned the 38-year-old and catapulted him back to the bad old days, undoing the good work he'd done in the intervening years.

And that's the problem.

Whenever Schumacher's remarkable achievements are discussed, his reputation will be haunted by those split seconds of cold, calculated and clinical cheating. And that will be what stops him being the greatest.