The 16-year-old Stoner, from Kurri Kurri in New South Wales, will make his 250cc Grand Prix debut just four weeks after breaking his shoulder in testing at the Catalunya circuit in Barcelona, Spain.  And McCoy, 29, from Camden on the outskirts of Sydney, is ready to go after breaking his leg in testing at Estoril, Portugal, in February.

McCoy will line up on his tried and true 500cc Yamaha in the renamed premier racing category, MotoGP, formerly the exclusive domain of two-stroke machines up to 500cc but now also open to four-stroke bikes of up to 1000cc.

The Japanese GP heralds the much-anticipated direct confrontation between the new-era and traditional machines after months of European winter testing.

The reigning 500cc world champion, Italian Valentino Rossi, who clinched his title at last year's memorable Australian Motorcycle GP at Phillip Island, is heading the four-stroke challenge on the new five-cylinder Honda.

Rossi topped the time sheets at last weekend's final test at Suzuka, with Japanese team-mate Tohru Ukawa ? also on a four-stroke Honda - the only other rider within a second of his time.

Leading Yamaha's four-stroke charge is another Italian Max Biaggi, who was runner-up to Rossi for last year's crown and won the 2000 Australian Motorcycle GP.

Rossi and Biaggi are sure to resume their intense rivalry on the track, with the Honda seeming to have the early edge over the Yamaha M1.

McCoy, a three-time GP winner in 2000, is sticking with the two-stroke Yamaha on which he set faster times than Biaggi.  The Australian has a new team-mate this year - young American John Hopkins, following the return of Japanese rider Noriyuki Haga to Superbike racing.

While McCoy concedes the four-strokes have a power and acceleration advantage, he feels the two-strokes will still be highly competitive this season.

"I got in behind Max at Suzuka (last weekend) and the M1 (four-stroke) certainly gets off the turns quicker than the 500 and has a higher top speed," McCoy said.

"But the 500 can go deeper and harder on the brakes and is a bit quicker into the corners, so at some tracks it is going to be interesting over a race distance.

"At Suzuka I thought Max might pull away, but I stayed with him for a couple of laps and was able to check out the corner lines he is using on the M1."

Also keeping the two-strokes near the front throughout the 16-round championship, which visits Victoria's Phillip Island on October 18-20, will be the reigning 250cc world champion, Japan's Daijiro Katoh, Italian Loris Capirossi and Brazil's Alex Barros - all on Hondas.

Suzuki has brought forward the development of its four-stroke machine to put 2000 world champion American Kenny Roberts, and Spaniard Sete Gibernau on the Suzuka grid, while Aprilia has installed McCoy's former team-mate, Frenchman Regis Laconi, on its new, but relatively untested, four-stroke.

The new MotoGP regulations have triggered a tyre war in parallel with the technical battle between the bike manufacturers and the 990cc four-stroke motors.

Three tyre companies - Michelin, Dunlop and Bridgestone - will be official tyre suppliers this year. By comparison, in Formula One car racing there are only two,  Bridgestone and Michelin, while Bridgestone is the rookie in MotoGP.

McCoy's Red Bull Yamaha team made an early off-season switch to Dunlop, and the immediate dividends were a string of sub-record lap times in testing.

"Dunlop have some tyres that suit my style and they are prepared to build new ones as I need them for different tracks, which is something I haven't had before," McCoy said.

World title favourite Michelin has retained a powerful line-up of riders and teams, not least Rossi and his Honda factory colleagues, plus Yamaha M1 riders Biaggi and Spaniard Carlos Checa.

In the 250cc category, Stoner, who last year competed in both the British and Spanish 125cc championships plus scored 125cc wildcard rides at the British and Australian GPs, will join an impressive line-up, including former 125 world champions Roberto Locatelli, of Italy, and Emilio Alzamora, of Spain, plus Italian Marco Melandri and Spanish sensation Toni Elias.

Teenager Manuel Poggiali, from San Marino, will defend his hard-won 125cc world title, riding against established stars such as Japan's Youichi Ui and Masao Azuma and Italians Lucio Cecchinello and Simone Sanna.