For your viewing pleasure and eco-driving enlightenment, may I present a graph showing cruising speed vs. fuel consumption in the Micra SR automatic that Nissan loaned me a little while back.
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UPDATE: also see post #8, below, for the results for the Micra S 5-speed loaner.
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(Yes, I'm still going through my notes, posting up interesting info.)
Route: This info was gathered on a straight & level, 1.6 km / 1 mile stretch of dry road using a ScanGauge that was calibrated against 2 actual fill-ups. The numbers are averages of 2-way runs for each speed (except for the highest one), to average out effect of wind & grade. There were never any vehicles ahead of me in my lane (no drafting effect).
Weather conditions (Mon, Jul 14, 2014):
- Temp: 16C
- Wind: WSW 2 kts
- Press: 101.1
- Humidity: 93%
A/C was off, and cruise control was used for the test: set once for each speed, cancelled with the brake at the end of the first run and "resumed" for the run in the opposite direction to ensure the same speed each way.
- I went by the Micra's indicated speed (which we know reads a little high). So shift the plot to the left by the right amount if you want to fine tune it even more.
- That blip in the numbers between 50 & 60 km/h is there because the Micra's automatic transmission shifts into top gear and locks the torque converter right around 58 km/h under light load, making that the car's most efficient cruising speed (lowest engine RPM in top gear).
Does this mean you should expect to get 5.7 L/100 km if you head out on a highway trip and set the cruise at 100 km/h?
Not necessarily. Ever heard the saying "your mileage may vary?"
- These numbers don't take into consideration the extra fuel burned getting up to speed.
- The route was very flat; in hills, you'll likely get worse mileage.
- There was almost no wind (and the 2-way runs average out its effect). In a headwind/crosswind you'll get lower fuel economy; in a tail wind you'll get better.
- 1 person on board: no passengers & no cargo.
- Weather was very MPG-friendly: mild temps. Winter conditions will have a big negative effect on these numbers.
- No A/C use -- A/C drops the Micra's fuel economy.
- The road was dry and smooth (pavement in good condition).
- etc. etc.
All of these variables will affect the numbers.
I do this test with every car I own to have a benchmark of what I can expect on a round trip under good conditions. (Also I want it for comparison purposes, since I tend to modify my cars to improve mileage.)
The moral of the story: speed kills MPG.