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Old 04-20-2020, 12:24 AM   #10 (permalink)
Aero Wannabe
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Join Date: Dec 2007
Location: NW Colo
Posts: 685

TDi - '04 VW Golf
90 day: 47.98 mpg (US)
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Test Data Day Two

My Day One results were inconclusive so I decided to do another round of testing. Day 2 was 59 degrees with the wind averaging 7 mph but occasionally gusting to 10-15 mph (as per weather radio from the airport just north of the test road). I increased the speed for all runs to 65 mph to try to highlight aerodynamic differences.

A1 runs Day 2 east/west average mpg- 48.45
B1 runs Day 2 east/west average mpg- 48.6
A2 runs Day 2 east/west average mpg- 50.65

The testing was still somewhat inconclusive. The differences could have been from wind changes or other traffic on the road.

I went home and changed to my summer tires and rims. My summer tires are replacements of the stock Goodyears which are getting thin. They are mounted on VW Mk III GTI 9-spoke replica Minilite rims. I also have coroplast wheel covers held onto the spokes with zip ties. Again I left the car running while I removed or installed the wheel covers to keep the same cruise control setting for all these runs. The C runs are the naked alloy rims and the D runs have the smooth wheel covers on over them.

C1 runs east/west average mpg- 56.45
D1 runs east/west average mpg- 54.1 (coroplast covers on)
D2 runs east/west average mpg- 56.1
C2 runs east/west average mpg- 51.75

On my last run of the day my west bound data may have been corrupted. I encountered some slower traffic and had to brake before the end of the run. I got only 47 mpg for that leg. I averaged the C runs with the spinning alloy spokes open to the air and got 54.1 mpg. I averaged the D runs with smooth wheel covers and got 55.1 mpg. There is not a huge difference but the advantage goes to the alloy rims with the coroplast cover by 1 mpg. I have some thoughts on this but will update more tomorrow.

The biggest difference was the change from snow tires on steel rims, covered or not, to lighter rims and summer tires- almost 5 mpg or roughly a 10% improvement!
60 mpg hwy highest, 50+mpg lifetime
TDi=fast frugal fun

Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.

Last edited by COcyclist; 04-26-2020 at 11:53 AM..
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