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Discussion Starter #1
So this car has a feature where if you step on the throttle and release, it will shift from any gear into neutral. Sport mode disables this because once you hit the throttle against to accelerate, there will be a bit of delay as the PDK goes back into gear. You can also do a shift up from 7th gear to manually get into coast mode. I find myself in cruise control on the highway and engaging coast mode after deactivating cruise control because when the PDK is disengaged, the car coasts with less drag, allowing it to get further and maintain speed without touching the throttle and increasing MPG. If you do this well enough, you can get 36+ mpg.

Question is why doesn't deactivating cruise control automatically put the car in coast mode (in neutral) and is there a way to set it to do this...to remove a step of having to use a paddle shifter to upshift ever time you deactivate cruise control...
 

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Nope.

Actually I very rarely use CC because I prefer to let the car coast on the highway.

So this car has a feature where if you step on the throttle and release, it will shift from any gear into neutral. Sport mode disables this because once you hit the throttle against to accelerate, there will be a bit of delay as the PDK goes back into gear. You can also do a shift up from 7th gear to manually get into coast mode. I find myself in cruise control on the highway and engaging coast mode after deactivating cruise control because when the PDK is disengaged, the car coasts with less drag, allowing it to get further and maintain speed without touching the throttle and increasing MPG. If you do this well enough, you can get 36+ mpg.

Question is why doesn't deactivating cruise control automatically put the car in coast mode (in neutral) and is there a way to set it to do this...to remove a step of having to use a paddle shifter to upshift ever time you deactivate cruise control...
 

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Does the car ever go into coast mode while CC is on? Do you have to do anything under normal circumstance to activate coast other than release the throttle or upshift?
 

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Does the car ever go into coast mode while CC is on?
Not to my knowledge. My experience has been that activation of either Cruise Control or the "Sport" button will lock out (prevent) the coast function.
 
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Nope.

Actually I very rarely use CC because I prefer to let the car coast on the highway.
Cool. I use CC on the highway all the time, when traffic is light enough to allow it. Continuously fiddling with the throttle and checking the speedo (to make sure I'm not speeding) takes time and attention. When I have the CC set, I don't have that distraction, and can spend more time maintaining situational awareness of the traffic flow.
 
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I'm pretty sure the car went into coast while the cruise was on, the last time I used cruise control. I was using cruise and coast as an attempt to get more mpgs, when I drive the fuel economy is pretty sad.
 

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I'm pretty sure the car went into coast while the cruise was on, the last time I used cruise control. I was using cruise and coast as an attempt to get more mpgs, when I drive the fuel economy is pretty sad.
My (non-ACC) 2013 absolutely will not coast in cruise under any conditions. Really perplexing why they'd disable that. I wouldn't be surprised if they fixed it in 2014 and/or 2015 cars.
 

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Discussion Starter #8
I'm confused... Some of you can get the car to coast while in cruise? mine definitely doesn't but I see zero reason as to why it can't..and why they don't fix it via software update.
 

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My (non-ACC) 2013 absolutely will not coast in cruise under any conditions. Really perplexing why they'd disable that.
I don't see the present setup as being odd... The purpose of CC is to maintain vehicle speed, and the computer controls the engine & transmission to achieve that function. In "coast", the engine is disengaged from the drivetrain and the fuel mixture goes down to idle. When the car is in coast mode, the CC can't function; because the engine is disengaged.
 

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I don't see the present setup as being odd... The purpose of CC is to maintain vehicle speed, and the computer controls the engine & transmission to achieve that function. In "coast", the engine is disengaged from the drivetrain and the fuel mixture goes down to idle. When the car is in coast mode, the CC can't function; because the engine is disengaged.
That's not even remotely how a cruise control system works. It's all drive by wire, and the system that disengages the PDK clutch has nothing at all to do with the control loop that regulates the vehicle speed. They could enable coasting during cruise, they just didn't, at least at the time my car was built.
 

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That's not even remotely how a cruise control system works. It's all drive by wire, and the system that disengages the PDK clutch has nothing at all to do with the control loop that regulates the vehicle speed. They could enable coasting during cruise, they just didn't, at least at the time my car was built.
I never said it wasn't drive by wire - of course it is. That point is irrelevant. What do you think "regulates the vehicle speed?"...the RPM of the transmission output shaft which is a function of the engine rpm and the trans gear. And you don't have ANY control of vehicle speed while the coast mode is activated; because coast mode puts the transmission into neutral (the trans output shaft is disconnected from the engine crankshaft).

The purpose of CC is to maintain a CONSTANT speed. Coasting has nothing to do with maintaining speed - the car will gain or lose speed depending on the slope of the road. Allowing coast mode to take over control of the engine/trans while in CC mode defeats the purpose of the CC.

I didn't say that coast mode couldn't be added via software, I simply said I didn't see anything odd about the present setup that excludes coast mode while in CC mode. The only time coasting could realistically be allowed during CC would be when the car is rolling downhill and the increased forward motion due to gravity is offset by mechanical friction and aero; such that constant speed would be maintained without CC. How often would that situation occur? Probably not a whole lot.
 
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I never said it wasn't drive by wire - of course it is. That point is irrelevant. What do you think "regulates the vehicle speed?"...the RPM of the transmission output shaft. And you don't have ANY control of vehicle speed while the coast mode is activated; because coast mode puts the transmission into neutral (the trans output shaft is disconnected from the engine crankshaft).

The purpose of CC is to maintain a CONSTANT speed. Coasting has nothing to do with maintaining speed - the car will gain or lose speed depending on the slope of the road. Allowing coast mode to take over control of the engine/trans while in CC mode defeats the purpose of the CC.
So it's beyond the ken of German engineering to, oh, I don't know, exit coast mode when necessary to maintain the cruise control setpoint speed?

We must be talking past each other, because otherwise this entire subthread makes no sense.
 

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Discussion Starter #14 (Edited)
I never said it wasn't drive by wire - of course it is. That point is irrelevant. What do you think "regulates the vehicle speed?"...the RPM of the transmission output shaft which is a function of the engine rpm and the trans gear. And you don't have ANY control of vehicle speed while the coast mode is activated; because coast mode puts the transmission into neutral (the trans output shaft is disconnected from the engine crankshaft).

The purpose of CC is to maintain a CONSTANT speed. Coasting has nothing to do with maintaining speed - the car will gain or lose speed depending on the slope of the road. Allowing coast mode to take over control of the engine/trans while in CC mode defeats the purpose of the CC.

I didn't say that coast mode couldn't be added via software, I simply said I didn't see anything odd about the present setup that excludes coast mode while in CC mode. The only time coasting could realistically be allowed during CC would be when the car is rolling downhill and the increased forward motion due to gravity is offset by mechanical friction and aero; such that constant speed would be maintained without CC. How often would that situation occur? Probably not a whole lot.
yes I totally get why the car doesn't coast while cruise control is on. As you mention, it's to maintain speed and that doesn't happen when you coast down hill. Instead cruise control downshifts to engine brake.

Id want the ability for the deactivate function to always put the car in coast when sport mode is off so I don't need to feel like a ninja quickly hitting the cruise lever down followed by pressing one of the panel shifters in.
 
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