When using road speed to know when to switch gears, you should:

Question

There are two indicators that determine when you need to shift into a higher gear. One indicator is the engine speed (rpm). You should read your vehicle's manual to learn its rpm range and shift up when you reach the top of that range. The other indicator is road speed (mph). You should learn which speeds each gear can accommodate, then keep an eye on the speedometer and shift up as needed.

Accepted Answer

Learn what speeds each gear is good for and shift up when necessary.

Answer

Watch other vehicles and try to keep pace.

Answer

Watch other trucks and shift when they shift.

Answer

Use the speed limit as a guide.