A commercial motor vehicle driver transitions from operating a fully loaded combination unit to driving an unladen (empty) combination vehicle under dry roadway conditions. When applying standard stopping and braking procedures, which statement accurately explains why the empty vehicle requires distinct braking precautions compared to the loaded vehicle?
- The empty vehicle has less tire traction on the roadway, making it more susceptible to wheel bounce and early wheel lockup, which can lead to longer stopping distances.Answer
- BThe air brake system experiences substantially greater brake lag because empty trailer brake chambers require higher air pressure thresholds before mechanical pushrods actuate.
- CThe auxiliary engine retarder must remain set to its highest output level to offset the reduced mechanical friction between the brake linings and drums.
- DThe brake pushrod stroke decreases automatically when the vehicle is empty, preventing the S-cam from rotating far enough to achieve optimal drum contact.
Answer
The empty vehicle has less tire traction on the roadway, making it more susceptible to wheel bounce and early wheel lockup, which can lead to longer stopping distances.
Commercial motor vehicle braking systems are calibrated to provide optimum stopping power when the vehicle is fully loaded. When a combination vehicle is unladen, there is less weight pressing the tires against the pavement, drastically reducing tire traction. Consequently, aggressive brake application easily causes the wheels to lock up and the vehicle to bounce, resulting in loss of steering control, increased skid probability, and greater total stopping distances.
Step-by-Step Solution
Key Concept
Braking characteristics and traction limitations of empty commercial vehicles
Estimated Time:1m 30s