Automatic Transmission: Shift To Sport While Driving

[nunusguy]

Gotta clear this up...

Engine braking (to "mansplain" further) uses the engine's internal friction (as drivers, we don't really care whether it's mechanical friction or pneumatic resistance) to slow down the car.

This helps in the mountains because you can regulate your speed on looooooong downhills without having to use the brakes. If you're on the brakes for ten or twenty minutes straight, they might overheat, and then you're SOL.

In manual transmissions, you'd achieve this by downshifting, of course. In older automatics, it's the same thing -- move the lever to "2" or whatever. In our CVT Civics, "S" or "L" will do the job (and in the Sport trims with paddle shifters, you can click down to a shorter ratio via the left paddle, too).

nunusguy, I haven't been on the same route, so I don't know exactly what warning signs you saw. But I've generally seen only two types -- signs to encourage engine braking (such as "Use Low Gear - Downhill 15 miles") and signs to prohibit it, the latter of which usually in residential areas to tell big trucks to not use their "Jake brakes" to avoid disturbing people in their homes.

So to dovetail this back into the original question, "Is it OK to shift between Drive and Sport while moving?" ---

Yup, it's fine, just like it was always OK to shift between D, 2, 1, etc., in traditional fully-mechanical automatics. It's even less of a concern now because the CVT is entirely computer-controlled and will not choose a ratio that'd cause the engine to over-rev. The capability to do this on-the-move is to allow engine braking (or, rarely, if the uphill is long and gradual, and the transmission can't decide for itself which ratio to use).

Thanks BarracksSi, that was a very comprehensive and helpful response and I appreciate it, you da man !

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[kalvin126]

So to further explain.. lol I agree with all of what BarracksSi said.

Gotta clear this up...

In manual transmissions, you'd achieve this by downshifting, of course. In older automatics, it's the same thing -- move the lever to "2" or whatever. In our CVT Civics, "S" or "L" will do the job (and in the Sport trims with paddle shifters, you can click down to a shorter ratio via the left paddle, too).

You activate engine braking in modern cars just by releasing the accelerator pedal. You do not need to decrease gear ratio. In automatics/CVTs it is still the case. You do not want to lug the engine so you have to be sure RPMs do not drop too low (below 1.5k RPM~). Automatics take care of this for you by automatically reducing gear ratio when needed.

The rate of deceleration is determined by RPMs though; Higher the RPM, the higher the deceleration.

Gotta clear this up...
nunusguy, I haven't been on the same route, so I don't know exactly what warning signs you saw. But I've generally seen only two types -- signs to encourage engine braking (such as "Use Low Gear - Downhill 15 miles") and signs to prohibit it, the latter of which usually in residential areas to tell big trucks to not use their "Jake brakes" to avoid disturbing people in their homes.

Also another reason why some states discourage use of engine braking is because some times it is not enough to moderate your speed as in prevent your car from accelerating due to the descent grade. The 152 highway in California has a mountain part where I can go down hill and my car still accelerates to 90 mph even during engine braking.

The beauty of engine braking, though, in my opinion is that it saves gas. No gas is used. I personally let go of the gas pedal as early as I can; such as if I see a red light ahead, anticipating a light turning red or about to turn green. If I could just decelerate enough but still keep the car in motion while waiting for the light to turn green, I save gas by not having to accelerate from a dead stop. I am a Eco-nut as you could maybe tell lol. I easily get 45~MPG in the city in our Civics. Though sometimes turning off Eco mode and flooring it some times feels so awesome lol.