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2019+ BMW 3 AND 4-SERIES FORUMS (G2x Generation) General G20 Sedan / G22 Coupe / G26 Gran Coupe Discussions Which gear to use?

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      03-20-2020, 08:10 PM   #23
mcjohnsonsg
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Quote:
Originally Posted by M40iSFR View Post
Maybe someone who can help with the answer will come along...
I was trying to help you understand the context of your question. The answer is not in theoretical calculation. It is in real world experimentation, as one of the previous posts suggested. You will never, ever, drive in the same set of circumstances that would be modeled by your proposed theoretical calculation. So the theoretical calculation will never be correct, and will frequently be wildly wrong. The more meaningful solution is to run a series of tests in different scenarios, monitoring the mpg readout on the car, and get a "feel" for what is most efficient in a range of circumstances.

I am an engineer with 28yrs of experience, a global technical director in charge of 900 technical staff. You can choose to consider this or not. Your choice.
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      03-20-2020, 08:17 PM   #24
M40iSFR
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Maybe someone who can help with the answer will come along...
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      03-20-2020, 10:10 PM   #25
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Quote:
Originally Posted by M40iSFR View Post
Maybe someone who can help with the answer will come along...
No one even cares to attempt to try to answer it anymore. You got your answer here, you just choose not to understand and comprehend it.

Don't think you realize that even if you can, it makes of no use since you're driving style is different every time and there's tons of variances that wouldn't ever be equal for this test or experiment to give you the right answer or whatever you're looking for.
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      03-21-2020, 05:17 AM   #26
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Quote:
Originally Posted by M40iSFR View Post
I've previously always driven six speed manual cars; 3rd gear was for around town, 4th dual carriageways, 5th the motorway. My new car has an automatic transmission with 8 forward gears to choose from - too many!

Say I'm sticking to the 120 KPH speed limit, 8th gear is most efficient, but gutless. I could easily use 7th, or 6th. I'm wondering what the real word difference in fuel economy is. Shouldn't be too difficult to calculate?
To be honest I am somewhat baffled by the question but maybe booking a session on a rolling road might get, or help you to get, the answer you seek. A rolling road removes many of the variables and you can 'drive' without many of the normal distractions.

As an aside, I had the pleasure of working in Zurich for three years (walking round the lake was the best commute i ever had!) and from memory the place was pretty jammed up with traffic during the day in any event!

We all have our own preferences, but may I ask if you have tried using the 8 speed box in automatic mode - it really is a fine piece of engineering that works exceptionally welll, and the paddle shift is there to intervene if you feel the need. Personally I wouldn't be without it, but each to their own
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      03-21-2020, 05:27 AM   #27
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Maybe someone who can help with the answer will come along...
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      03-21-2020, 05:39 AM   #28
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To be honest it is a very specific question and quite a strange premise. I doubt anyone else drives the way you suggested. So the answer, as I see it, is for you to test and update us all with your findings.

Maybe someone else will help. Or maybe you will enlighten us. 😊
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      03-21-2020, 03:01 PM   #29
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Talking

Quote:
Originally Posted by M40iSFR View Post
Maybe someone who can help with the answer will come along...
Or not!!

Can't say we haven't tried
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      03-21-2020, 06:06 PM   #30
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Quote:
Originally Posted by M40iSFR View Post
I've previously always driven six speed manual cars; 3rd gear was for around town, 4th dual carriageways, 5th the motorway. My new car has an automatic transmission with 8 forward gears to choose from - too many!

Say I'm sticking to the 120 KPH speed limit, 8th gear is most efficient, but gutless. I could easily use 7th, or 6th. I'm wondering what the real word difference in fuel economy is. Shouldn't be too difficult to calculate?
The only way is to test, with instrumentation, to be really accurate. Simulations will be very complex, and/or a bit of guesswork.

I know when I wanted economy figures for a particular vehicle in different gears, two way tests over a particular stretch of road, using OBC figures, was the easiest way to clearly see the changes of MPG in different gears, at the same speed.

Even with BSFC maps for your engine and data for the road load of the specific vehicle, I believe you still need some of the engine mapping detail. For example, regarding emissions control strategy over the rev band and engine load.

BTW, I'm not sure how you arrive at specific gears for different driving scenarios, surely load dictates much of gear selection, not the speed.

AT will use the gear most suited to the conditions. So easy to drop a gear when demand is higher, either through throttle control, or paddle/shifter intervention.

BTW, cruising at 120 KPH in 8th shouldn't be any issue at all, can be much lower and still useable. AT drops a gear or two immediately, when load is applied.
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