[azraelswrd]

Depending on where and how you drive, aero mods can only do so much. From my own experiences/experiments smooth hubcaps and rear skirts do very little for my FE because I drive about 80% city and 20% highway (and "highway" is 45-55mph at most).

Plus it's hard to say if a mod is having any significant effect after a tank/refill worth of driving because so many variables can factor in along the way from driving style since that is difficult to maintain the same at all times. One trip you can be getting 50mpg and another trip, a traffic jam and headwind get you 30mpg. This is why instant digital feedback is critical here that a vac gauge cannot or rather its limited by what it can offer.