Didn't MythBusters disprove all of those theories of improving gas mileage via tonneau covers, toppers, mesh tailgates, etc?
They never tested with a topper, only tailgate up and down, mesh tailgate, tonneau, and no tailgate. Here are the stats they posted.
* Tailgate down: 5.2 gallons/hr @ 55mph. 1.2 gallons/hr @ 25.
* Tailgate up: 5.0 gallons/hr @ 55mph. No reading for 25mph given, but tailgate up was once again confirmed as more efficient.
* Hardcover over pickup bed: 5.0 gallons/hr @ 55mph. 1.2 gallons/hr @25mph
* Tailgate mesh: 5% more efficient
* Tailgate removed: about the same as tailgate up and hardcover
I just put a topper on my truck...and switched to synthetic. If I get any better MPG I have no way of knowing which did it or which contributed the most. Oh well!
The best MPG I got was 17.8 on the drive back to Carlsbad from the SF Bay Area. I made it all the way from San Jose to Diamond Bar before filling up, I think it was 376 miles? I could've gone farther, but I don't want to push it. I don't think I've ever put more than 22-23 gallons in my truck.