Before the 2006 season, Penske changed engine manufacturers from the under-powered Toyota to the more powerful Honda in its Dallara IR-05 car after Toyota withdrew from IndyCar. Castroneves started fifth and led 40 laps for his first series road course win in the Grand Prix of St. Petersburg. He took a second successive victory at Motegi, leading 184 laps from pole position to lead Wheldon by 42 championship points entering the Indianapolis 500. After qualifying second, handling difficulties caused him to strike the turn four concrete barrier, leaving him 25th after 109 laps. Castroneves won the Bombardier LearJet 500 after strategic errors by his teammate Hornish and CGR before tire problems at Kansas and a sixth place at Kansas lost him the points lead to Hornish. A victory at Michigan International Speedway gave Castroneves a one-point lead over Hornish going into the final race in Chicago. A fourth place put him third in points with 473.