View Single Post
Old 12-01-2007, 11:44 PM   #1 (permalink)
Batman Junior
MetroMPG's Avatar
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,213

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 53.56 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)
Thanks: 3,790
Thanked 6,626 Times in 3,437 Posts
2006 in review: mods vs. technique. And the winner is...

Driving technique won over mods by a pretty wide margin: 37.5% vs. 28.0%. Though you'll have to buy into my "comparison" method to believe it. It's pretty inexact (to say the least...)

Tallying just the mods ...

5.2% tranny swap

10.3% alternator optional

2.3% kardboard kammback

2.3% mirrors

5.7% grille block & rear wheel skirts

2.2% undertray

= 28% total theoretical improvement over base from measured mechanical/aero mods

I'll be the first to admit this tally is flawed on several levels: 1) the weather conditions weren't the same for all tests; 2) the speed wasn't exactly the same for all tests (but close to 55 mph); 3) the effects of individually tested aero mods can't simply be summed because their effects interact with one another ... the car is probably more or less than 28% better with all the mods in place. But the car was never driven with all of them in place at one time and then without.

Driving technique ...

To do this comparison, I looked at 3 tanks in Firefly #1 which were predominantly city driving. When I was using that car, I wasn't employing coasting of any form, or P&G/codfishing, and there were none of the mods listed above.

Firefly #1, 3-tank tally: 1474 km, 83% city driving ... 5.2 L/100 km / 54.0 mpg (Imp) / 45.0 mpg (US)

Blackfly, 3-tank tally: 1724 km, 83% city driving ... 3.3L/100 km / 86.5 mpg (Imp) / 72.0 mpg (US)

If you do the math, that actually works out to a 60.2% improvement for the Blackfly.

The biggest flaws in this comparison are: 1) it assumes the "base" cars are identical (which they were on paper, but probably weren't in reality) ; 2) the Blackfly has some mechanical & aero mods on it that the other car
didn't have. Based on the values in the mods list though, we can correct for these mods:

- 5.2% transmission advantage
- 10.3% alternator advantage
- 1.2% aeromods advantage (calculated based on avg. city speed of 25 mph vs 55 mph for the tests)
- 6.0% rolling resistance (this is a WAG - the Blackfly has LRR tires and higher pressures than the first Firefly had)

-22.7% total deductions (this is actually a liberal estimate, because the Blackfly was not running alternator-less, nor with all aero mods, and the taller tranny was only in place for 2 of the 3 tanks)

= 37.5% estimated difference due to driving technique

Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: Oops, I did it again! Bought another cheap, 3-cylinder Mirage. Mods in progress...
Ecodriving test: Manual vs. automatic transmission MPG showdown

has launched a forum for the efficient new Mitsubishi Mirage - fuel efficiency info for Geo Metro owners - electric car conversion on a beer budget
  Reply With Quote