What gear should an automatic car use when going downhill?

[VonCharles]

Automatic cars need to adjust the gear selection based on the steepness of the slope. Use lower gears for steeper slopes and higher gears for gentler slopes. Below are relevant explanations: Methods for controlling speed: For manual transmission cars facing long or steep downhill roads, you can shift into D2 or D3 to control the gear. D2 means the transmission won't shift beyond 2nd gear, while D3 limits it to 3rd gear. This allows full utilization of engine braking to effectively control vehicle speed. Principle of engine braking: Engine braking refers to the drag effect created by the compression resistance, internal friction, and intake/exhaust resistance generated during the engine's compression stroke on the driving wheels (manual transmission cars can be parked on slopes while in gear using this principle).

[NaomiMarie]

I've been driving automatic transmission cars for over a decade, and the safest way to handle downhill slopes is to use lower gears, such as shifting to L gear or manual mode's 1st or 2nd gear. This is because the engine assists in braking and deceleration, reducing wear from frequent brake usage. Especially on long steep slopes, continuous braking can cause brake discs to overheat and fail, potentially leading to accidents. Once when driving on mountain roads, I neglected to use lower gears and ended up with smoking brakes—fortunately, I didn't lose control. Now, I always slow down and shift gears in advance, which not only protects the braking system but also saves fuel. Different car models may have different gear names; for example, S gear is also a good option—check your owner's manual to familiarize yourself with your vehicle. In terms of safety, controlling speed downhill is crucial, and developing this habit is absolutely worthwhile.

[RowanDella]

I just started learning to drive, and my instructor taught me to shift gears when going downhill, so I've gotten used to using the S or L gear. Simply put, lower gears help stabilize the speed and prevent the car from sliding uncontrollably, as the engine slows the car down, avoiding excessive use of the brakes. If you stay in D gear all the time, there's a higher risk of burning out the brake pads. I tried it on a slope in my neighborhood, and after shifting to a lower gear, the car noticeably slowed down, making driving much more reassuring. When encountering a steep slope, slow down first before making adjustments—some cars have a downhill assist button that can be used in combination. Don’t forget to check tire conditions and brake fluid; regular maintenance helps prevent accidents. New drivers should practice a few more times to get the hang of it. Automatic transmissions aren’t foolproof—manual intervention is crucial in key situations.

[MacSienna]

From the perspective of automotive principles, using a lower gear for engine braking on downhill slopes: automatic transmissions at lower gears result in higher engine RPM, where resistance consumes energy, reducing the tendency to accelerate, thereby protecting the brakes. I prefer manually locking into 1st or 2nd gear, letting the engine handle the braking task; on long slopes like highway exits, this avoids brake fade leading to loss of control. Technically, different transmissions like AT or CVT perform slightly differently, but the core is maintaining a stable speed. Regularly checking transmission fluid is also crucial to ensure smooth shifting.