Downshifting to Prevent Brake Failure

As a friend of mine and I drove through a steep hilly region recently, we observed something that may have amounted to a very dangerous situation.

As we overcame a high hill in our car, we looked forward to coasting our way down the other side. To our surprise, the downhill trek was much steeper than the one we had just taken uphill. A garish sign bearing a caricature of a freight truck cautioned us:

Warning: 6% Grade Ahead. Use Engine Brakes.

Mountain Road Driving

Not having driven in the mountains before, my friend asked me, "Should I be concerned about that sign? What does it mean?"

"Yes," I answered, "you do need to pay attention to it."

I further explained to my friend that the sign was a little misleading in that it seemed to address only large freight trucks. Despite the fact that we were driving in a passenger car, I explained that the laws of gravity applied to our small car just as equally as it did to big trucks.

Steep Grades

To start with, I explained that the 6% grade was actually pretty steep.

In plain words, for every 100 feet a vehicle drove down that road, that a car or truck would drop 6 feet in elevation. While this may not seem like a big deal, one can try parking one's car on a slight incline, stepping out, releasing the parking brake, and trying to stop the car with one's body after the car has rolled perhaps 15 feet or so. It's well near impossible! Momentum has built up, and only a good pair of brakes can stop the vehicle.

In a passenger car weighing somewhere between one and two tons, stopping is usually not a big deal. Passenger car braking systems do a good job with stop and go traffic on a level surface. However, what if one were to apply the brakes continuously on a steep downhill decline? This kind of situation is exceptional, and push your car's braking system to its limit âˆ' and perhaps beyond into the danger zone.

Brake Failure Due to Overheating

Because no vehicle's braking system is meant to be applied continuously, driving in mountainous or hilly areas is a less-than-ideal situation that clearly makes this point.

When one starts "riding" the brakes continuously down a steep hill, the brakes most soon become hot. Depending on how steep the grade and how long the the ride down is, car or truck brakes can overheat and fail.

To continue the story I had started above, my friend and I observed an older year luxury car several hundred meters front of us as it went downhill. The car's telltale red lights showed us that the driver was braking pretty much continuously. After some time, we saw a wisp of smoke develop behind the car. My friend and I were able to smell the smoke: the distinctive odor of burning brake pads. In a manner of a few moments, that thin wisp developed into a rather obvious smoke trail.

Fortunately the driver had seen the smoke also and was able to successfully pull over and stop his vehicle. As my friend and I drove by, I saw smoke rising up from the front wheel wells.

"Engine Brakes"

"Wow, that could've been bad!" my friend remarked.

I agreed and then suggested that my friend all of the advice on the sign at the top of the hill.

I explained that the "engine brakes" concept specifically referred to large freight trucks, but applied to passenger cars just as well. I went on to say that truckers face the same problem with brakes overheating as passenger cars do - and actually even more so because of the heavy load they are carrying. So instead of using their brake pads to slow themselves down, they used their engine as a brake by downshifting several gears.

Downshifting on The Hill

I suggested to my friend that she use the same technique truckers used by downshifting her car's engine a gear or two. Open to the idea, she did so under my instruction and with some caution.

The vehicle we were riding had an automatic transmission with four forward gears, the highest of which was an overdrive "OD" - a very high-speed gear. I suggested downshifting one notch into "D" âˆ' which on that vehicle served as a generic forward gear suitable for high-speed cruising in the city.

After downshifting that one gear without applying any gas to the pedal, the engine revved up noticeably and helped slow the car down. After the car had some time to slow even more, I suggested that my friend apply the brakes to slow down even more, and then shift down one more gear to see what happened. The engine revved up even more, and the car decelerated much more noticeably.

At this point, we were only going perhaps 35 mph, which was a fair match for the speed at which my friend's second gear was designed. Because we didn't want to go any slower, nor well as overstress the transmission, I cautioned my friend not downshift any further.

Further on down the hill, our vehicle sped up to 45 mph or so, thus causing the engine to wind up also. To stem this acceleration, my friend only had to apply the brakes occasionally.

After some time we got to the bottom of the hill, where my friend shifted back up to overdrive. My friend expressed her thanks for the experience, and followed up by asking for some explanation on what had just happened.

Downshifting Saves Brake Pads

The idea is simple. Basically passenger car breaks are good for quick stops. However, under a sustained heavy braking load, they can overheat and produce smoke, as we had noticed with the other car.

As an alternative to burning up one's brake pads, a driver can use their gears as a braking system. Because both the engine and transmission require lots of energy just to get them moving, a driver can use the appropriate gear to leverage this inherent friction as an alternative form of braking.

The result? The diversion of all that downhill energy into the transmission and engine, and less use of the conventional brake pads. On the safety side, this reduces the chance of brakes overheating and failing. On the practical side, this also reduces wear and tear on the brake pads, thus allowing the driver to use the brakes over a longer service life.

Be Knowledgeable âˆ' Use Some Caution

Both truckers and experienced passenger car drivers can confidently use their lower gears to slow down on steep hills. You can, too. Before trying this, make certain that you keep in mind a few simple rules.
Speak with a knowledgeable friend or your mechanic about your car's "yellow line" or "redline" engine revolution limits. Have them explain to you how to use downshifting to slow your car down.
When shifting down a gear while driving downhill, your engine will "rev up" and experience some increased load. You don't want to overstress your car's transmission or engine by allowing them to "rev" too high. Relieve some of the added stress by applying the brakes firmly for a few moments to help lower the engine's revolutions.
Only shift down one gear at a time.
While driving downhill in a lower gear, very steep hills may cause your car to continue to accelerate. Simply apply the brakes firmly for a few moments to keep this acceleration in check. If you use the correct gear to leverage your engine as an "engine brake", you will need to apply the brakes only occasionally.

On busy, narrow or one-lane downhill roads, don't slow down too much lest you might be struck from behind.

When used effectively, downshifting while driving down steep inclines will transfer a great portion of the braking action to your car's transmission and engine. For most cars this extra stress is not a major concern. Using your car's engine as a brake allows your car's regular brake system to serve as a kind of backup for when further deceleration is needed.

In the end, this helps keep your speed in check while driving downhill, as well as reducing the wear and tear on your brake system.

Drive safely!

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