I understand what an overdrive is (lower revs, good for highway), but can someone explain if that is the only time i should be using it? Is there more too it? Its the 4th gear right?

I understand what an overdrive is (lower revs, good for highway), but can someone explain if that is the only time i should be using it? Is there more too it? Its the 4th gear right?


over drive means gears with a ratio below 1:1,
if a gear ratio is 0.99:1, then that is an over drive gear
So both automatics and manual transmission have over drives.
As for a 4th spd auto, most of the time over drive is 4th gear, thats what the button is for. On/off, changing from 4th to 3rd.
But some cars have both 3rd and 4th (last two gears) in over drive. So they can't use a botton like that, or OD off means only 1st and 2nd gear.
What I do is I just leave in drive. My car doesn't have a OD button, and I am too lazy to shift to 4th gear and move it back to 5th (D) between local and highway. I just let the computer take over.