In the Race Now settings, set your Field Size to 1 and your Weekend Length to include a Practice session (this should give you plenty of space to experiment with your top speed). Load into Daytona International Speedway (this track allows you to easily reach top speed). Drive to track in your Practice session. Run a few laps and note your Top Speed. Pause the game and choose Settings > Controls > Controller. Adjust the R2/RT Saturation slider down 5 notches. Return to the track and drive a few more laps and note your Top Speed (it should be higher). Keep adjusting the Saturation slider downwards 5 notches at a time and see how it affects your Top Speed. At some point, you will see no improvement in your Top Speed. When this happens, adjust the Saturation back up 5 notches. This controller should now be properly calibrated to reach Top Speed. Please note that this setting will be global for all controllers and may need to be readjusted if you change controllers.