Part of the improvement came from the softer, grippier Pirelli Supercorsa SC tires I was running, and some of it was the track. Different tracks play to different bikes' strengths, and thus far I've only raced the RC at Chuckwalla. Sonoma is distinctly different—different speeds, different rhythm, and most importantly, different pavement. Sonoma's surface is far less abrasive, so the Pirellis wore beautifully while still offering the improved traction, stability, and line holding that I experienced when I first tried the tires at Chuckwalla. The Supercorsa SCs are far and away the best tires I've used on the RC390.