Will an Automatic Transmission Car Roll Back?
3 Answers
If an automatic transmission car is in neutral without applying the handbrake or stepping on the brake, it may roll forward or backward. Reasons for rolling on a slope: The driver does not step on the brake or apply the handbrake, causing the vehicle to roll backward due to inertia; Insufficient power in neutral, or the vehicle is idling with limited power, and the slope is too steep, leading to insufficient force when in D gear, resulting in rolling; Some automatic transmission models experience delayed power delivery when releasing the brake and pressing the accelerator, causing the vehicle to roll. On gentle slopes, the D gear can overcome the backward force generated by the vehicle's weight without pressing the accelerator. However, if the slope is too steep or the vehicle's weight increases, the backward force will also increase. If the downward force exceeds the forward driving force generated by the engine in D gear, the vehicle will naturally roll backward. Methods to prevent rolling: Automatic transmissions have a manual mode or S (Sport) mode. Proper use of these modes can effectively prevent rolling. Step on the brake, switch to manual mode or S mode, use the "+" sign to shift to first gear, apply the handbrake, release the brake pedal, and press the accelerator to ensure the throttle input is greater than the force released by the handbrake, guaranteeing sufficient power output. Once the vehicle starts moving forward, the driver can feel it. If the handbrake is fully released and the throttle is maintained, no additional force is needed if the vehicle can climb the slope. If the vehicle remains stationary without rolling, deeper throttle input is required to drive the vehicle uphill; For automatic transmission vehicles without hill-start assist, the simplest and most effective method to prevent rolling is still to use the handbrake for a smooth start. When starting, first apply throttle until the front of the car lifts slightly and the handbrake lever feels lighter, then slowly release the handbrake to prevent the vehicle from rolling backward.
Last time I drove my sister's automatic SUV up a steep slope in the urban village, it gave me a real scare! Even though it was in D gear, the car started rolling back when the slope exceeded 15 degrees. I later learned from the 4S dealership that automatic transmissions also depend on configuration: older models without hill-start assist can roll back if the transmission gears aren't fully engaged when you release the brake. Nowadays, most new cars come equipped with HAC (Hill-start Assist Control) functionality. For example, my Toyota Corolla Hybrid can hold for two seconds after releasing the brake, giving me time to press the accelerator. However, I should remind everyone that in places like underground parking garages with epoxy flooring during rainy days, even with assist features, the car might still slip. It's best to engage AUTO HOLD in advance. Also, leaving the car in P gear on a slope for extended periods can damage the transmission gears. The correct practice is to engage the parking brake first before shifting to P gear.
12 years of driving automatic transmissions tells you: YES! Especially when driving my wife's old Nissan Sylphy CVT to the wet market, you need to be extra careful when queuing on slopes. The key issue is that the torque converter doesn't provide enough torque at idle, just like being in neutral. Here's a trick: when stopping on a slope, don't release the brake immediately. First, lightly press the accelerator to raise the RPM to 1000, feel the car's forward momentum, then release the brake. Cars with auto-hold are even more convenient, and now most domestic cars under 100,000 RMB come standard with this feature. Remember never use N gear on steep slopes - last week I saw a BMW owner roll back and bump the bumper.
