S is for sport. If you're driving on twisty country roads and want to keep the RPM up as you wind through corners, the "S" position is where you want to be. In "S", the transmission holds lower gears longer for more power as you come out of the curves. "The "B" position favors lower gears, too, but for a totally different purpose. Just as you might shift a conventional transmission to Low on a long downhill grade; you can shift into the "B" position to increase engine drag and help slow the Corolla while coasting down a hill.