Should I be using fourth or fifth as my main gear when driving long runs?
Fifth gear uses probably four or five horsepower just to run the gear. If you were towing a trailer, ran into a headwind or were on a constant uphill, you’d be far better off, fuel economy wise, to use less throttle in a lower gear like fourth. Fifth gear isn’t as robust as fourth either and will wear out quicker. Fourth gear, in a gearbox, is generally straight through and not using any gears at all, where fifth is using just about everything.