CDL General Knowledge TestCombination Vehicles (if applicable)Hard
What is the primary danger of 'bobtailing' (driving a tractor without a trailer) on slippery surfaces compared to driving a loaded combination vehicle?
- AIncreased risk of engine overheating due to reduced load.
- BReduced traction on the drive wheels, making jackknifing more likely.
- CSlower stopping distances due to the absence of trailer brakes.
- DDifficulty in maintaining highway speeds due to lack of aerodynamic stability.
Show answer & explanationAnswer & explanation
Correct answer: B. Reduced traction on the drive wheels, making jackknifing more likely.
When bobtailing, the tractor's drive wheels have significantly less weight on them because the trailer's weight is absent. This drastically reduces traction, especially on slippery surfaces. With less traction, the drive wheels can easily lock up during braking or spin during acceleration, leading to a loss of control and increasing the risk of the tractor jackknifing.
Why the other options are wrong
- A. Reduced load typically reduces engine strain, decreasing overheating risk.
- C. A bobtail tractor usually has shorter stopping distances than a loaded combination vehicle.
- D. Bobtail tractors are generally more maneuverable and faster, not slower, on highways.
Bobtailing Hazards
Bobtailing (driving a tractor without a trailer) reduces weight over the drive wheels, leading to significantly decreased traction and increased risk of jackknifing, especially on slippery roads.
- Less weight on drive axles.
- Higher risk of wheel spin and lock-up.
- Requires careful driving on slippery surfaces.
Memory trick: Light in the rear, spin in the gear.