gear choice

[MetroMPG]

<img src="http://old.soliton.net/old/images/tach.jpg" align="right">

Feb 28/06
3:30pm - 4:00pm

car: 1998 pontiac firefly (geo metro); 3-cyl; 1.0L; 5-speed. warmed up with approx 30-40 minutes of mixed city/suburban/exurban driving.

route: 1.8 km / 1.1 mi., slightly rolling - *maybe* 5-10 ft elevation chg over 1.8 km (didn't feel like driving out to my usual test route)

weather:

Air Temperature (ATMP): 18.0 °F / -7.8 C

Wind Direction (WDIR)...WSW ( 240 deg true )
Wind Speed (WSPD).......22 kts (40.7 km/h / 25.3 mph)
Wind Gust (GST).........25 kts (46.3 km/h / 28.8 mph)

http://www.ndbc.noaa.gov/station_page.php?station=supn6

wind note: i probably wasn't subjected to *full* wind conditions shown above; this weather station (roughly 5-10 km from the test route) is fully exposed in open water on the St Lawrence River, and the 1.8 km stretch of road i used has portions which are tree-lined, and other portions which are protected by some land elevation to windward.

results:

test speed 65 km/h / 40.4 mph +-1

all readings taken going in the same direction (s/w).

gear...rpm.....mpg(US) ScanGauge readings (mpg = avg function)

5......2080....55.9
4......2500....47.0
3......3495....41.5
2......5175....25.9

for reference: going in the opposite direction along the same 1.8 km route at the same speed:

5......2080....66.7 (nice wind effect, eh?)

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notes:

- take this as "snapshot" FYI info only. the mpg precision is NOT good due to the small sample, short course length, uni-directional (non-averaged) runs, and i didn't use cruise control.

- man i *hated* doing that 2nd gear run. my car doesn't have a factory tachometer. without that scangauge (digital tach) i would have sworn i was going to see pistons flying through the hood. aggh! the noise! but i knew ahead of time (from my service manual) that the rev limiter cuts in at 7000 rpm, so i had revs to spare.

- i just don't like revving engines like that. sheesh. the things i do for "science". (okay, i love revving engines on the race track, but i haven't done that for a few years... and never in a 3-cyl! )

- i should get bonus points in the gaslog for dragging down this tank's mpg in my quest for knowledge!