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Old 04-20-2020, 11:48 AM   #14 (permalink)
Aero Wannabe
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Join Date: Dec 2007
Location: NW Colo
Posts: 692

TDi - '04 VW Golf
90 day: 47.98 mpg (US)
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I realized last night as I was entering the test data that if you only look at the averages, my results show the covered rims give a slight improvement over the bare alloy rims. As I noted in that post my final run may have been impacted by heavier traffic. Also, those runs were later in the day when winds are typically higher, gusting and variable here in the high desert. This makes it harder to get good data. I have tried various forms of the wheel covers over 12 years of driving VW TDI and my tank mpg averages would always go down when I used them. My best mpg tanks all occurred on summer tires with the bare alloy rims. I was puzzled by this so I assumed my wheel covers were somehow deflecting and trapping oncoming air. I doubled up on the wire ties. No improvement. My first attempt was larger, matching the widest part of the tire, so I tried a smaller set. No improvement. I assumed the ties through the spokes were too close to the center so I moved them closer to the circumference. No improvement. I purchased Julian Edgar’s new book- Modifying the Aerodynamics of Your Road Car, and found some information that could explain why I was not seeing positive results from this widely accepted modification.
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.
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