Which of the following instruments is NOT commonly found on a motorcycle?

The instrument that is not commonly found on a motorcycle is the thermometer. While motorcycles typically come equipped with a speedometer, odometer, and tachometer, these gauges serve essential functions for monitoring speed, distance traveled, and engine RPMs. The speedometer helps the rider maintain a safe and legal speed, the odometer tracks mileage for maintenance and fuel efficiency, and the tachometer provides information on engine performance, allowing the rider to understand when to shift gears.

Conversely, a thermometer, which measures the temperature of the engine or outside conditions, is not a standard feature on most motorcycles. While some motorcycles may have temperature gauges specifically for monitoring engine temperature, it is not a typical instrument found across all models as the other three are. Therefore, recognizing that a thermometer is less commonly included in standard motorcycle instrumentation is crucial for understanding the typical motorcycle dashboard layout.