Source of that information? I'll put up with them full time, if shown good evidence that they make that much difference. My current routine is to use them only on long trips, when speeds are generally higher, so aerodynamic drag becomes a bigger factor than in local short trips.
You are unlikely to find anything other than anecdotal evidence. Anything scientific is going to require strict controls that aren't representative of real word driving. Really the best you can do, as others have mentioned, is try both with and without and see what gives you the best results for your driving style and routine. That does necessarily mean that your results will be indicative of MPG difference for anybody else.
I've been thinking of doing the same thing, though I'm not sure it's worth the bother. I guess I'd be more inclined to uncover the alloys if mine weren't black.
I'm sure Toyota engineering has either done that test, or else measured the difference in drag and done the analysis to translate that drag difference into fuel consumption difference under specified conditions. I'd settle for knowing the difference in drag coefficient. with vs. without wheel covers.
These are the responses Toyota gave to others who have asked. One may have better luck asking specifically for drag numbers.
Thanks, NPG! Love their consistency (and their sloppy dangling modifier, too)! The "possibly" is silly; either removing the wheel covers will definitely "lead to a decrease in fuel economy," or it definitely will not.
