CDL General Knowledge TestDriving SafelyHard
A commercial driver is preparing to drive a vehicle equipped with a manual transmission on a long, steep downgrade. To maximize control and prevent service brake overheating, what is the correct downshifting technique?
- ADownshift one gear at a time, allowing engine RPMs to increase before selecting the next lower gear.
- BSkip multiple gears at once to quickly reach a very low gear, then maintain speed with the service brake.
- CShift to neutral and coast, using the service brake for speed control.
- DEngage the clutch and hold it in while applying the service brakes to slow down, then select a lower gear.
Show answer & explanationAnswer & explanation
Correct answer: A. Downshift one gear at a time, allowing engine RPMs to increase before selecting the next lower gear.
Proper downshifting on a downgrade involves selecting a gear that allows the engine to control speed without excessive use of the service brakes. Downshifting one gear at a time, matching engine RPMs, ensures smooth engagement and effective engine braking, preventing shock to the drivetrain and maintaining control.
Why the other options are wrong
- B. Skipping multiple gears can cause a sudden, dangerous increase in RPMs and shock to the drivetrain, leading to loss of control.
- C. Shifting to neutral and coasting is extremely dangerous and illegal, as it removes engine braking control.
- D. Holding the clutch in disengages the engine from the drivetrain, eliminating engine braking and relying solely on service brakes, leading to overheating.
Downshifting on Downgrades
A technique for manual transmission vehicles where the driver selects progressively lower gears while descending a hill to utilize engine braking, preserving service brakes and maintaining control.
- Prevents service brake overheating and fade.
- Requires matching engine RPMs to road speed for smooth shifts.
- Must be done one gear at a time for optimal control.
Memory trick: One gear at a time, rev match with rhyme!