I highly doubt that a study has been made but I would love to know the drag coefficient delta that the following conditions/accessories cause: 1. Waxed body (decrease drag by ?) 2. Clean body (baseline) 3. Dirty body (increase drag by?) 4. Off-road type grime (increase drag by ?) 5. Side moldings (increase drag by?) 6. Shark fin antenna (Increase or decrease drag by?) 7. Mud flaps (increase drag by?) I would love if a Toyota engineer with access to a wind tunnel or the Prius v CFD simulation could answer these nuances. Basically that is what I would like to know, are these all just nuances or can each of these things have 2-3% impact on MPG? On the first point: Does it make economic sense to wax your car prior to taking a long highway roadtrip? Will the wax job pay for itself in a long roadtrip, or at least “subsidize” half the cost of a wax job? Is there any outside accessory that noticeably reduces drag coefficient on the Prius v? I would consider buying something that improves the MPG so that it pays for itself in a few years. (Besides LRR Tires)
I would doubt that wax makes a car have less drag, but I would think that its ability to shed dirt and not have the buildup of dirt, would help the drag. Removing the outer mirrors and not running mudflaps would help the most.
I remember mudflaps as having a small but definitely measurable effect on MPG. OTOH, the $ you save by not having any are offset by the additional "soap" and labor used cleaning the lower half of the body more frequently especially if you have a white car. And the back hatch gets dirty quickly too due to the Kamm effect. I prep for a long trip by RainX'ing the front and wear windows, the mirrors and front side windows. As much for bugs as for rain.
The folks at Ecomodder.com have a roll-down protocol and spreadsheet to calculate the rolling and aerodynamic drag. Ask Mr. Google and you can probably find others. Bob Wilson
