Here's why you shouldn't use D or N while driving downhill in an auto transmission

Jason · Jan 16, 2021 11:00 AM

Image credit: Temple of VTEC Asia

Recently, one of our readers posed a very interesting question: How to drive downhill correctly in an automatic transmission? Actually, the basics of how engine braking works has been covered here previously, and it applies to all transmission types.

Therefore, we will not go into technical details of downhill driving. Instead, let's discuss the dos and don'ts of downhill driving, seeing that this activity is indeed quite a favourite pasttime of Malaysian drivers. Also, the focus will be on the automatic transmission in this segment, even though the principles can be applied across most other transmissions. 

Dos

O/D off button in an older Perodua Myvi

First things first, you should always select a lower gear when navigating downhill. You can usually see options L or 2 (sometimes this could also be 'S') in your gear selector, and a small button on the lever itself for 'Overdrive off'. The lower the gear, the better effect engine braking has on helping slow down your car, thus reducing the strain on the braking system.

Select 'S' when going downhill

In cars equipped with paddle-shift, just select gears 2 or 3 and you're generally getting enough engine braking to safely navigate downhill. That said, you cannot solely rely on engine braking to get you downhill safely. You'd hear of many 'drivers' boasting that they do not brake whilst going downhill. Well, that is just plain untrue.

The most important thing is to learn to brake efficiently and effectively. What does this mean? Brake only when you need to, and apply optimum pressure to slow the car down. Since engine braking is already assisting in slowing down the car, your usage of brakes can be adjusted too.

Apply high pressure braking in short bursts

For example, it is better to brake at high pressure for 3 seconds, versus braking at medium pressure for 5 seconds. Shortening braking periods allow the pads and rotors to cool down in between braking, and cumulatively, this will prevent your brake system from cooking itself prematurely. 

Don'ts

For one, you should not drive downhill by leaving your transmission in D. In this mode, your transmission map is geared (pun intended) towards fuel economy, and will select the highest gear as soon as possible. That being the case, engine braking will not be allowed to do its work effectively to help slow the car down.

Neither should you coast downhill in N. At least in D mode, there is still some semblance of engine braking. By using N, you are disengaging the engine from the transmission entirely, meaning there is zero engine braking. Because of this, your brakes are left to shoulder the entire car's weight, you and your passengers included. Sounds like a bad idea, right? It is. 

Looks cool.... or does it?

One more thing to avoid is riding your brakes. This usually is the main cause of brakes overheating. How does one ride the brakes? You are on the brake pedal for long periods, unnecessarily, and not applying enough brake pressure at the same time. Many drivers do this subconsiously.

Image credit: Cycling About

As always, do make sure your car is well-maintained before going on a downhill drive. With regards to the braking system, make sure your brake fluid levels are fine, and that your brake pads and rotors have sufficient life in them. It isn't a big problem if your car can't start moving, but it is a BIG problem when your car can't stop.

Always ensure your brake system is in good condition before doing a downhill run

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