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?)

---

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!

[krousdb]

Great job! It confirms what I had been seeing with the SuperMID but your testing is much more scientfic than my casual observations.

Thanks for taking one on the chin for the greater good. But I'm sure with your newfound knowlege that you will make up for it by the end of the tank. ;-)

[MetroMPG]

newfound knowledge? get a taller transmission!

i'd be curious to know for the sake of comparison where other people's supermid/scangauge-equipped cars are at 40 mph in top gear on a relatively flat road.

of course it's hard to compare what with wind and temp differences (though i could average my 2 windward/leeward top gear runs).

[krousdb]

Originally Posted by MetroMPG

newfound knowledge? get a taller transmission!

i'd be curious to know for the sake of comparison where other people's supermid/scangauge-equipped cars are at 40 mph in top gear on a relatively flat road.

of course it's hard to compare what with wind and temp differences (though i could average my 2 windward/leeward top gear runs).

I would be happy to run those tests if I could find a relatively flat road. Thats a tall order around here.

[diamondlarry]

Originally Posted by MetroMPG

newfound knowledge? get a taller transmission!

i'd be curious to know for the sake of comparison where other people's supermid/scangauge-equipped cars are at 40 mph in top gear on a relatively flat road.

of course it's hard to compare what with wind and temp differences (though i could average my 2 windward/leeward top gear runs).

I'll try to remember to check that tomorrow. If I remeber right though, it's somewhere in the 60-70 range. On a recent trip from dropping my daughter off at church, I averaged just over 63 mpg(Scanguage) for the 4& 3/4 mile trip. I was travelling between 35 and 45 most of the time. Since I had the Scanguage in trip mode I'm not sure what the instantaneous mpg was.

[JanGeo]

Boy I gotta wonder about going 40mph in 2nd . . . that is really reving it for sure, I have done it a few times and my Geo sounds pretty good at that rpm.

[diamondlarry]

Originally Posted by MetroMPG

newfound knowledge? get a taller transmission!

i'd be curious to know for the sake of comparison where other people's supermid/scangauge-equipped cars are at 40 mph in top gear on a relatively flat road.

of course it's hard to compare what with wind and temp differences (though i could average my 2 windward/leeward top gear runs).

I checked my Scanguage readout at 40 mph in 5th gear and was a bit surprised. It read between 75 and 80 mpg with an occasional spike into the mid 80's. Of course, if I touched the throttle at all, the mpg dropped like a lead baloon back to normal levels.

[philmcneal]

yup 70km/h is indeed the sweet spot to cruise (1800+) rpm's for me in 5th gear. Although at 60km/h it feels that I'm lugging the engine (1500) rpms (or not i dunno) but the car feels more smooth cruising at 2000 in 4th gear though.

Too bad I don't have a scangauge, wonder if I really should cruise at 1500 rpms in 5th... I'll never know i guess!

Besides.. i rather take it out of gear at 70km/h and turn off the engine

[SVOboy]

I've been cruising my mom's camry at 1k rpms, 25 mph in 5th,

[JanGeo]

My xB is about 2 to 1 in 5th gear so the lowest it likes is about 1000rpm 20mph and gives about 50-55mpg on a level road but what happens is if I stay at the speed the engine doesn't get lubricated enough. If I throw a rev with the clutch in the mpg goes up to about 66mpg for a little while. Anywhere from 20-30 mph gets high 45-50 MPG going faster 35-40 MPH is good typically in the 42-43 MPG range.