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The 1998 Grand Prix motorcycle racing season was the 50th F.I.M. Road Racing World Championship season.
1998 Grand Prix motorcycle racing season Wikipedia
Mick Doohan and Honda continued to dominate the 500 class with the Australian taking 8 victories and Honda winning all but one race. Simon Crafar winning the British Grand Prix for Yamaha's lone victory. After being shocked by 500 class rookie Max Biaggi's opening round victory in the Japanese Grand Prix, Doohan went on to claim his fifth world championship in as many years, finishing off the season with four consecutive wins.
A controversial finish marked the 250 title race. Aprilia team-mates Tetsuya Harada and Loris Capirossi both went into the final race in Argentina with a chance to win the title, Capirossi leading Harada by 4 points. With one corner to go, Harada was in second, with Capirossi third, which would have given Harada the championship on tiebreak. Entering the final turn, his bike was struck from behind by Capirossi's machine, sending both riders off the track. Valentino Rossi took the win with Capirossi recovering to finish in second and claiming the title. Afterwards, Aprilia would release Capirossi from his contract.
Kazuto Sakata would win his second 125 title for Aprilia after a tight battle with Tomomi Manako and Marco Melandri.Riders marked with light blue background were eligible for Rookie of the Year award.