At constant vehicle speed, which gear ratio will lead to higher engine RPM?

The gear ratio significantly influences the relationship between the engine RPM and the vehicle speed. A higher gear ratio means that the engine must turn more times for each rotation of the wheels. Consequently, at a constant vehicle speed, if you select a higher gear ratio, the engine RPM will increase.

In the case of a 3:1 gear ratio, for every three rotations of the engine, the wheels rotate once. This higher ratio compared to lower ratios such as 2:1 or 4:1 indicates that for the same speed, the engine will be operating at a relatively increased RPM because of the need to compensate for the additional turns required by the wheels.

The lower gear ratios result in less engine RPM for the same vehicle speed since the engine turns fewer times per wheel rotation. Conversely, a gear ratio of 4:1 or 5:1 will require even more engine RPM to achieve the same speed, but since the question specifies identifying which will lead to the highest RPM at constant speed, the 3:1 choice is optimal.

Ultimately, selecting a gear ratio that is higher, like 3:1, will result in a noticeable increase in the engine's RPM while maintaining a steady vehicle speed.