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And finally, the aero topper (mod G).
I started thinking about making a new topper when I had to carry a freezer that was 1/2" taller than the hinge of the Leer topper previously on the truck. A hinged lid would have eliminated the need to unbolt and raise the topper twice. I also wanted a way to carry larger things, such as a snowblower.
And then, I found Ecomodder.com and started to read about the advantages of aero toppers.
The truck cab is narrower up near the top than down at the top of the box. The topper must fit behind the tapered cab. The hinged lid of an aero topper can be built two different ways. The lid can be rectangular or trapezoidal. If the lid is rectangular, the topper sides need to twist inward toward the rear of the box. If the lid is trapezoidal, the topper sides can be built to match the side taper of the cab and simply cut to a triangular shape. The trapezoidal lid is easier to make. My brother's aero topper has a trapezoidal lid, my topper has a rectangular lid. Photos of both are in my profile.
The rectangular lid has another disadvantage. My Canyon cannot carry full sheets of plywood with the tailgate fully up. It will carry plywood with the tailgate at the halfway setting.
I believe that either design will have the same drag. I know that both toppers have smooth airflow over them. My topper collects zero road salt on the top and sides in the winter, even when the windshield gets loaded with salt.
The topper is held closed with a pair of pins connected to a lockable T-handle. A pair of gas struts hold it open.
Construction is two layers of 3/16" thick underlayment plywood over wood frames. This plywood is sold as 1/4" nominal thickness. All wood was sealed with epoxy, then painted with hardware store gloss enamel.
The topper was installed 12-12-2010. Results:
December 2010 thru February 2011: 28.11 MPG (5.0% increase). The real increase should be slightly better than that because I got careless about tire pressure that winter.
So there it is - A-B-CDE-F-G testing. Not the ideal ABA testing, but it gives me real world relative improvements. My current plans are to continue as is to get summer 2011 MPG with the aero topper. I'm not sure what I'll test next. I'm thinking about air dams, belly pans, or maybe test 100% gas instead of E10.
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