What does the term "gear ratio" refer to in a vehicle's transmission?

The term "gear ratio" specifically refers to the relationship between the number of teeth on the driven gear and the number of teeth on the driving gear in a transmission system. This ratio plays a critical role in determining how power is transmitted from the engine to the wheels, impacting the vehicle's performance characteristics.

When you have a larger number of teeth on the driven gear compared to the driving gear, the gear ratio is higher, which means that the vehicle will have more torque, but lower maximum speed. Conversely, a lower gear ratio—where the driving gear has more teeth than the driven gear—allows for higher speeds but less torque. Understanding gear ratios helps in optimizing vehicle performance for various driving conditions, such as acceleration or cruising.

The other choices do not accurately define gear ratio. The speed of the vehicle is a result of how the transmission and gear ratios work together with the engine's power output, not a definition of gear ratio itself. The amount of torque refers to the twisting force produced by the engine, which is influenced by gear ratios but is not a direct description of what gear ratio means. Lastly, the size of the tires can affect overall vehicle dynamics and speed but has no direct relation to the definition of gear ratio.