Gear ratios can be used to increase ________.

Gear ratios are critical in the mechanics of a vehicle's transmission system, serving as a means to modify the amount of torque delivered to the wheels. When a lower gear ratio is employed, it results in a greater torque output when the engine's power is transmitted to the drivetrain. This is particularly advantageous in situations such as starting from a stop, climbing steep grades, or towing heavy loads where increased torque is necessary to overcome inertia or resistance.

Essentially, the relationship between the gear sizes ensures that for every rotation of the engine (input), a proportionally greater force is applied at the wheels (output) when the correct gear ratio is engaged. This aspect of torque multiplication is vital for effective vehicle performance in various driving conditions.

The other options, while related to vehicle performance, do not accurately capture the primary role of gear ratios. Speed can be affected by gear ratios, but typically, higher gear ratios lead to higher vehicle speed at the cost of torque. Friction is a factor in transmission efficiency but is not directly increased by altering gear ratios. Power is also not directly increased by gear ratios; rather, gear ratios help manage the existing power output from the engine to achieve the desired effect on torque and speed.