Which aspect is typically increased as you raise the numerical gear ratio in a rear axle?

When you raise the numerical gear ratio in a rear axle, you typically increase the towing capacity. A higher gear ratio means that the wheels turn fewer times for each revolution of the driveshaft, which enhances the ability to pull heavy loads. This is particularly beneficial in towing scenarios, as it allows for greater torque to be transmitted to the wheels.

Higher gear ratios are often implemented in vehicles designed for towing because they help maintain engine power in situations requiring significant exertion, such as hauling trailers or heavy equipment. This means that as you increase the gear ratio, you optimize the vehicle's setup for demanding tasks, enhancing its ability to handle weight and providing better acceleration when towing.

In contrast, other aspects like speed, torque, and fuel efficiency behave differently with changes in gear ratios, with a higher numerical ratio generally leading to decreased maximum speed, increased engine torque at the wheels (but not the torque output of the engine), and potentially lower fuel efficiency under normal driving conditions. Hence, the correct response is aligned with the increase in towing capacity provided by a higher numerical gear ratio.