03-18-2020, 04:33 PM | #1 |
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Which gear to use?
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? |
03-18-2020, 09:07 PM | #4 |
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If you're "sticking" to 120 kph then why do you need a gear with guts? 8th is best. If you you want to overtake someone you can easily downshift, the transmission is very quick.
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03-18-2020, 10:51 PM | #5 |
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03-18-2020, 11:14 PM | #6 |
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When you select drive, tilt the shift to the left which will engage sport mode and drop you down at least one gear. The BMW automatic is excellent and very fast. Stepping on the gas will get you into a lower gear in a hurry.
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03-20-2020, 09:56 AM | #10 | |
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Your fuel economy will suffer, and your 0-60 (etc.) speed will suffer but if you want control, throw the gear shift to the left and simply use your paddle shifters (I assume you have them). There is no real way to calculate the difference as your driving style will create wide variances. |
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03-20-2020, 04:09 PM | #11 |
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It must be possible to calculate.
At a constant speed of 120 KPH, gradient, rolling resistance, and all other variables constant. 8th gear would be say 1,000 RPM, 7th gear 1,500 RPM, etc. What's the difference in fuel consumption. Maybe something to do with gear ratios? Last edited by M40iSFR; 03-20-2020 at 04:15 PM.. |
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03-20-2020, 04:48 PM | #12 | |
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03-20-2020, 05:00 PM | #14 | |
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03-20-2020, 06:22 PM | #16 |
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Yes, it is possible. Car is calculating it and display the results right in front of you? Am I missing something here?
Last edited by hamera; 03-20-2020 at 06:33 PM.. |
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03-20-2020, 06:40 PM | #18 |
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03-20-2020, 06:54 PM | #19 |
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03-20-2020, 07:23 PM | #20 |
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You could never reproduce exactly the same conditions though. Even if you slammed on the brakes, reversed and drove the same section of road in a different. Tyre temp, engine temp, wind direction etc would all be factors.
It would have to be a theoretical calculation that keeps all other variables constant. If 6th gear ration was 2.3, 7th 2.1, 8th 1.9 you could calculate the increase in engine revolutions, and the relationship between fuel consumption. But I'm sure there are other factors too. People don't need to contribute if the thread doesn't interest them. Not looking for opinions. I'm happy to leave it here until an engineering geek finds it. Last edited by M40iSFR; 03-20-2020 at 07:29 PM.. |
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03-20-2020, 07:53 PM | #21 | |
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By the way, I am an engineer. |
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