Good to "see" you here, momorris. What vehicle are these wheel covers going on? That info might get you some more specific tips / pointers here.
Smooth wheel covers are definitely a good project, judging from the gains others have reported. I'm partially done on mine now. I can't imagine taking the time to do them in fiberglass but who am I to say it's not worthwhile?
Most guys seem to have used plastic serving plates or stamped metal pizza pie pans. I'm using perforated aluminum sheet with a stiffener on the back side, but I can definitely tell you that method is not quick.
If you go to the project library:
EcoModder Project Library - EcoModder.com
you'll find a few threads on smooth wheel covers. See the section "Project Section: Aerodynamic mods - fabrication", and you'll need to scroll down 15-20 threads there (currently) to see the ones on smooth wheel covers.
Here's a thread I've based some of my project on:
Simple Honda VX Alloy Wheel Covers (drilled acorn wheel nuts as attachment points)
That wheel cover should be suitable for most wheels, the attachment method is specific to Honda HX and VX and maybe for alloy wheels in general. Worth reading though.
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Check your tire pressure - keep it up !!
We've learned that diet has a closer relationship to cancer than we ever thought. Please see this Wikipedia article on
The China Study.
Driving Lean Burn '97 Civic HX, lotsa mods by now! '89 Volvo 240 is semi-retired. I did love that car though!