Which statement about proportioning valves is true?

Proportioning valves play a crucial role in maintaining optimal braking balance, especially during hard stops. When a vehicle brakes, the weight distribution shifts, causing the front brakes to bear more load than the rear brakes. This can lead to rear wheel lock-up, which can result in loss of control. Proportioning valves are designed to regulate and adjust the brake pressure applied to the rear wheels, ensuring that they do not engage too aggressively compared to the front wheels.

By providing better braking balance during hard stops, proportioning valves enhance safety and performance, allowing for effective braking without compromising vehicle stability. This means that the vehicle can stop more efficiently and safely under emergency conditions – an essential aspect of brake system design.

The other statements do not reflect the primary function of proportioning valves. They do not increase stopping distance, nor do they decrease brake balance; rather, they actively contribute to better balance. Additionally, while some modern vehicles may incorporate more advanced braking systems that reduce the need for traditional proportioning valves, they still play an important role in many vehicle designs to optimize braking performance.