Explain the term “axle” in a vehicle:

1. Correct answer: Shaft or system of drive shafts running the width of the vehicle, on which the wheels are installed.
2. The drive shaft that transmits the rotary motion from the gearbox to the differential.
3. A line along the vehicle, from bumper to bumper, which runs parallel to the vehicle's longitudinal axis.
4. The back beam of the chassis, to which the towing pin of the truck tractor is connected.

WhyAn axle is a shaft or set of shafts across the vehicle on which the wheels are mounted. A lengthwise line along the vehicle or a wheel drive is something else.