viper: it takes you time to react to seeing the light pop up, so when you shift 'at' the light, you're really shifting after the light, i.e., after the ideal time to shift. Only by a split second (most people's reaction time when they're not doing anything else is in the 0.1 to 0.3 second range, when you're busy driving maybe it's a bit longer), but that matters for drag...