Automotive

Downshifting in a semi-automatic

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  • Oct 26th, 2012 11:29 am
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I'm debating about the same question right now. Some people say Engine breaking helps reduce wear and tear in breaks while other say it puts too much stress on tranny to warrant the trade off. I've had jolting happen when I first used semi-automatic on my 2012 Skyactive Mazda 3. However, I did notice when I went slow enough (ie: 2000 RPM or lower), jolting is not noticeable and actually helps with emergency breaking (if traffic suddenly stops on highway). The semi-automatic tranny that I have will also downshift on its own if I go too slow to prevent engine damage, but does not shift up until I do it manually.

By default, the car's automatic system shifts up at about 2500 RPM, but I've seen it shift up in higher RPMs as well which confuses me as to when is the optimal point to make my shift. Engine sound becomes very noticable after 3000 - 3500 RPM.
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murdoc2k wrote:
Oct 24th, 2012 2:13 pm
I'm debating about the same question right now. Some people say Engine breaking helps reduce wear and tear in breaks while other say it puts too much stress on tranny to warrant the trade off. I've had jolting happen when I first used semi-automatic on my 2012 Skyactive Mazda 3. However, I did notice when I went slow enough (ie: 2000 RPM or lower), jolting is not noticeable and actually helps with emergency breaking (if traffic suddenly stops on highway). The semi-automatic tranny that I have will also downshift on its own if I go too slow to prevent engine damage, but does not shift up until I do it manually.

By default, the car's automatic system shifts up at about 2500 RPM, but I've seen it shift up in higher RPMs as well which confuses me as to when is the optimal point to make my shift. Engine sound becomes very noticable after 3000 - 3500 RPM.
Your car should have rev matched downshifts, especially when in S/M mode... Is it new? It's probably "adapting" to your driving habits.

Do note that throttle position controls when your transmissions shifts the car, if you didn't know... If you go full throttle it's not going to shift till redline. Go half throttle and it may shift at 3000 RPM. If you want it to shift earlier, just get off the throttle a bit, shift occurs, then floor it a bit more. That's what I do when I have to merge onto the highway while still keeping the engine RPMs under 3000 because the engine is cold.
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Swswswish wrote:
Oct 24th, 2012 12:46 am
If you drive an automatic just drive it the way it's meant to be made, if you want to drive like standard then get a standard car.

In a standard you can rev match when downshifting because between gears you're in neutral, it's impossible on an automatic. That's why there's a jolt when you downshift, you're engine braking.

And there's no point downshifting in you're coming to a complete stop.

PS, you never need to downshift to gear 1, your trans will be FUBAR.
Wondering how long it was going to be until this was stated.
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sandikosh wrote:
Oct 23rd, 2012 1:10 pm
Semi automatic? Half manual and half auto? Is there such a transmission.
My old '87 civic came with it. 3 speed and you have to manually move the lever to 1-2-3. Pretty peppy car for a carb'd 1.5L.
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Simply put its bad for your transmission and engine. However while driving on icy/slippery roads make use of your engine breaks if using regular break is causing your car to skid. But otherwise this would be a big no no.

(I have been driving manual Mustang for past 5 years with all season tires during all sort of weather conditions)
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quanvn wrote:
Oct 23rd, 2012 1:45 pm
Rev matching can eliminate the jolt you feel when downshifting.
This is getting into the double clutch downshift zone and it will be too complicate for normal guys, you have to know your car so well to find all the sweet spots...

For OP:
Put it this way, your auto trans itself downshift as well, without jolting! So, if your car can move if you just put your gear into D or OD, then I guess you don't need to do anything else... :facepalm:

For others:
So when you drive a manual, can you downshift without jolting? If you know how you know how to properly downshift! By matching speed, RPM and how to release the clutch...
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As mentioned by others, there should be no issues or negative impact to your vehicle if performed correctly, on a manual anyways.

1. Clutch in
2. Shift to Neutral
3. Clutch out
4. Rev match (blip throttle)
5. Clutch in
6. Shift to lower gear
7. Clutch out
8. Throttle

Timing is everything and it takes a bit to get the feel of your car but once you figure it out it does not seem complicated.....
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InTheNavy wrote:
Oct 24th, 2012 6:59 pm
As mentioned by others, there should be no issues or negative impact to your vehicle if performed correctly, on a manual anyways.

1. Clutch in
2. Shift to Neutral
3. Clutch out
4. Rev match (blip throttle)
5. Clutch in
6. Shift to lower gear
7. Clutch out
8. Throttle

Timing is everything and it takes a bit to get the feel of your car but once you figure it out it does not seem complicated.....
If your learn how to drive a tractor trailer, it has an "unsyncolized manual transmission" and therefore double clutch is the only way to shift up or down!

Now to do this on a "syncronized manual transmission"? I have never done it although I know how to do it, but I know some rally racer do this when downshifting on the Impreza STI or Mitsi EVO. Why? I am not a racer I don't know...
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murdoc2k wrote:
Oct 24th, 2012 2:13 pm
I'm debating about the same question right now. Some people say Engine breaking helps reduce wear and tear in breaks while other say it puts too much stress on tranny to warrant the trade off. I've had jolting happen when I first used semi-automatic on my 2012 Skyactive Mazda 3. However, I did notice when I went slow enough (ie: 2000 RPM or lower), jolting is not noticeable and actually helps with emergency breaking (if traffic suddenly stops on highway). The semi-automatic tranny that I have will also downshift on its own if I go too slow to prevent engine damage, but does not shift up until I do it manually.

By default, the car's automatic system shifts up at about 2500 RPM, but I've seen it shift up in higher RPMs as well which confuses me as to when is the optimal point to make my shift. Engine sound becomes very noticable after 3000 - 3500 RPM.
All tiptronic / sportshift / sequential sportshift trans are like that, even though you can control the gears, it's not mechanical like a standard transmission, it still goes through a computer. If the computer senses that the car will be performing poorly due to the current gear it will shift for you. So you can't redline, bog your engine, or stall. The reason your car won't shift up automatically is because you haven't redlined yet, only then will it automatically upshift for you.

An automatic transmission shifts depending on how you use the gas pedal. If you apply constant pressure it will shift at 2k-2.5k rpm because it knows you're just accelerating. If you slam on the gas, it will shift at a higher RPM, possibly won't even shift until you release the gas, because it's assuming you need more power (ex, you're passing someone) so it stays in the power band. There is no optimal point, the optimal point is what you decide based on how much power you need for the situation you're in. I shift at 2k rpm because I'm going in a straight line and I don't need the power.
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InTheNavy wrote:
Oct 24th, 2012 6:59 pm
As mentioned by others, there should be no issues or negative impact to your vehicle if performed correctly, on a manual anyways.

1. Clutch in
2. Shift to Neutral
3. Clutch out
4. Rev match (blip throttle)
5. Clutch in
6. Shift to lower gear
7. Clutch out
8. Throttle

Timing is everything and it takes a bit to get the feel of your car but once you figure it out it does not seem complicated.....
That is double clutching and you only need to do it on vehicles with unsynchronized gears. Usually only found on heavy transport trucks and specialty vehicles.

Almost all vehicles on the road have synchronized gears. Here is what I do.

1. Clutch in
2. Shift to lower gear
3. Rev match (blip throttle to generally ~1k higher than where you were at in the previous gear)
4. Clutch out and throttle again as necessary
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Others have mentioned rev-matching a manumatic when downshifting.
To put it even more simply, don't downshift with your foot off the throttle. The car will jerk if there's no built-in sport mode to blip the throttle. This wears the engine mounts and transmission.
Feather the throttle so the torque converter stays engaged then shift down. This will be smooth and stress-free.
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appleb wrote:
Oct 25th, 2012 9:37 am
That is double clutching and you only need to do it on vehicles with unsynchronized gears. Usually only found on heavy transport trucks and specialty vehicles.

Almost all vehicles on the road have synchronized gears. Here is what I do.

1. Clutch in
2. Shift to lower gear
3. Rev match (blip throttle to generally ~1k higher than where you were at in the previous gear)
4. Clutch out and throttle again as necessary
Anything you can do to save those syncros helps. 3rd gear is always the first to go, it's no fun to drive especially the 2.0 lire 4 bangers.. Even if you hit the sweet spot just right they still grind sometimes. It's just good practice.
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heyhey wrote:
Oct 25th, 2012 11:55 pm
http://www.youtube.com/watch?v=U8jZn2n9 ... e=youtu.be

Does this downshifting cause a lot of damage? I still brake when necessary, but for coasting I find this much more fun.
If it feels smooth to you and the car doesn't jerk violently then it should be fine. Just remember to feather the throttle on downshifts like I mentioned above which it looks like you are doing.
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I tried the "manual" function on a Hyundai

It was weird
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So the OP has yet to clarify what tranny he has? Does he have a torque convertor with tiptronics or a true dual-clutch semi-automatic? There is a big difference..
My old 328, when I downshift, there is a pull because it is a torque convertor. It slows down right away, and probably hurts the tranny but it was a lease.
On my S4, there's barely any feel when you downshift because it just rev matches but it will slow down faster. If I want to slow down a lot, I need to downshift twice to get any significant slowing down effect with the DSG. I don't think this hurts the tranny unless you downshift 2-3 gears at once. Even when I do that, my RPM goes from sub 2k to 4-5k? I push it harder than that on acceleration.

Mostly, I downshift to pass people but I use it to slow down on off ramps instead of braking and it allows for fasting acceleration after the ramp.
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