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Difficulty: MediumSpeed on Curves and Downgrades

Due to the reduced aerodynamic drag and mechanical friction of modern commercial motor vehicles, a driver may need to select a lower transmission gear to safely descend a steep downgrade than would be required to climb the same hill.

Answer: Answer

Answer

True. Modern commercial vehicles frequently require a lower transmission gear to descend a steep grade than to climb it due to decreased aerodynamic and mechanical drag.
The statement is true because modern commercial vehicles have aerodynamic bodies and low-friction drivetrains that offer minimal passive resistance going downhill, while powerful engines allow uphill travel in higher gears. As a result, relying on the climbing gear during descent yields insufficient engine braking, requiring an even lower gear to maintain a safe speed.

Step-by-Step Solution

1
Analyze the mechanical and aerodynamic characteristics of modern commercial motor vehicles.
Modern trucks feature streamlined bodies and low-friction components that generate less passive resistance to gravity on downgrades.
Passive drag factors directly influence how rapidly a heavy vehicle gains momentum on a decline.
2
Compare uphill climbing power against downhill retarding force requirements.
High-horsepower engines permit climbing steep grades in higher gears, but using that same gear downhill provides inadequate engine compression braking.
Engine braking capability decreases in higher transmission gears.
3
Determine the proper pre-descent gear selection procedure.
The driver must select an even lower gear before beginning the descent to control speed without overheating the foundation service brakes.
Proactive gear selection prevents thermal brake fade and runaway vehicle emergencies.

Key Concept

Transmission Gear Selection on Downgrades for Modern Commercial Vehicles
Estimated Time:45s
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Topics

Speed on Curves and Downgrades

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