Throttle ?

[voodoo22]

Depends on if you're going uphill or down, but if you're on a flat road you want to be in the highest gear at the lowest rpm which allows you to not put too high a load on the engine if you want the best possible efficiency.

Going uphill you need higher rpms, going down a hill you need less.

You have to go by feel. You'll know when you don't have enough rpms for what you're trying to do because the car will sound different and be unresponsive.