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Old 11-27-2007, 11:20 PM   #6 (permalink)
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Blackfly - '98 Geo Metro
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Last 3: 70.09 mpg (US)

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90 day: 55.97 mpg (US)

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90 day: 70.75 mpg (US)

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Better late than never, the Camry results:

Conditions were pretty ideal:

Temp: 25 C / Wind: 2 km/h SSE

Test approach was A-B-A, where...

A = no mods in place;
B = rear wheel skirts plus "fairing" behind OEM mud flap where the lower aft edge of the skirt was attached

(note: pic taken the next day after tape had been applied/removed several times already - it was a smoother installation for the test runs.)

- 3 bi-directional runs (6 one-way runs in each direction) for each of A,B,A
- Speed was 95 km/h, cruise control set once, cancelled by brake between runs, (flat, deserted road, little to no wind, no traffic in my lane; infrequent oncoming cars)

A average = 45.9 mpg (US)
B average = 46.3 mpg (US) - 0.7% increase over A

This was on a 2007 Camry hybrid.

But here's the problem: while the average of the six bi-directional A runs is less than the B runs, there was a big difference between the average of the first and second set of A runs:

In fact the average of only the 2nd set of A runs is bigger than the average of the B runs.

If you look at the Corolla test, you'll see something similar: the average of the 2nd set of A runs is higher than the first set (though not higher than the B runs).

All of which suggests to me that:

1) in both cases, the drivetrain was probably still warming up (making the car more efficient) while I was doing the runs. This skewed the results.

I had driven each car for about 25 minutes & 25 km before starting the runs.

2) if #1 is true, then if I had done a 2nd set of B runs after the 2nd set of A runs, the difference between the A & B averages likely would have been greater still.

Unfortunately, the only way to know this for sure would have been to do another set of B runs, and I didn't.


In conclusion, my testing bites.

Also, testing for small differences is difficult & time consuming.

And I need to drive much further to ensure a car is fully warmed up next time I try a test.
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