[jjguitar]

I hope someone can clear this up for me.

I am confused about RPMs and gearing in a car. This is how I understand it to be:

(We'll use and automatic as an example)...When starting from a dead stop, I am in first gear. After I hit a certain point, the transmission will switch to second gear, which will make the RPM gauge suddenly go down a bit. However, wouldn't the engine's rotation speed keep increasing? I always thought that if the gas pedal has a constant pressure, the engine rotation speed will increase evenly, and only the transmission determines the rate at which the tires spin...the RPM of the actual engine does not decrease with the RPM gauge. However, when they say that the overdrive gear (4th) increases gas milliage by lowering the RPMs, then my theory does not make any sense. Could someone explain what I have wrong here?

Thanks,
Justin