What two indicators determine when you should upshift?

The two indicators that determine when to upshift while driving a commercial vehicle are engine speed and road speed.

Engine speed, measured in revolutions per minute (RPM), indicates how hard the engine is working. Upsifting at the right RPM helps maintain optimal engine performance and efficiency. If the engine is running at too high an RPM, it can lead to excessive wear or even engine damage, so it needs to be shifted to a higher gear to lower the strain on the engine.

Road speed, on the other hand, gives you a sense of how fast the vehicle is moving. Upshifting at the appropriate road speed ensures that the vehicle stays within a safe operating range for both the engine and the vehicle itself. If you attempt to upshift at too low of a speed, you might stall the engine or create unnecessary strain on the transmission.

The combination of these two indicators—engine speed and road speed—provides a clear guideline for when to shift gears appropriately, ensuring smooth operation and longevity of the vehicle components.