1990 marked the beginning of the Rainey era with the Marlboro-Yamaha rider taking 7 wins and scoring points in every race but Hungary after he had already clinched the championship. Rainey's teammate was 1989 champion Eddie Lawson, but he was unable to defend his championship after breaking his left ankle in the first round and then severely shattering his right ankle the following round at Laguna Seca. Rainey on having Lawson as a teammate: “I just wanted to devastate Eddie. I don’t think he was ready for a team-mate like me. Maybe he thought he could control me, but at that stage I was past being controlled.” Rainey switched from Dunlop to Michelin tires this year.
The 1990 season continued the trend of crashes as riders tried to cope with the harsh power output of the V4 two-strokes. Honda put forth a proposition limiting the top class to 375cc and 3 cylinders, but that never caught on. Still, with 500cc lap times becoming stagnant, it was clear that something needed to be done.