There's an on-going discussion in the appearance mod board: http://www.priuschat.com/forums/mud-flapss...omy-vt8007.html The answer appears to be "nominal, if any at all..."
Hi Woody, I haven't checked Dans link, but if mudflaps (I assume the molded ones) effect mileage.... Intellectually I'd say yes, but practically.... Tuesday I went into the western mountains (big hills) of Maine and on a 200+ trip got 55.4 mpg. Friday I did a similar trip of 180 miles and got 54,x mpg. On a 30 mile pizza run 3 weeks ago we got 64.x mpg. I'd like more mpg but if the mudflaps are ruining my mpg I'd like to know what I'd be getting without them. I live in Maine on a dirt road, the mudflaps are essential. Gauge your need by that. If you're just putting them on for "coolness" I wouldn't bother; if they're needed for mud I wouldn't hesitate, they do make a huge difference. Practically I don't think they have a measurable influence on mpg. I had that question before installing them and came close to not installing. After installing them I realized that they rode in the wake of the tires. My opinion is that they have no effect at a reasonably high enough speed. Check Dans link though to get a number of opinions.
I agree. The obvious answer is yes, it will. Probably by a laughable amount too, what with the added weight and wind resistance and flappiness.
