Originally Posted by stevehnm
Well, I did a 1586 (within 1%) two way highway mile trip this weekend, and checked my mpg with my Scangauge. The good news is that although the initial mpg was off by various numbers up to 2.5 mpg (but sometimes less than 1) it eventually came in to the Scangauge reading during the tank (asymptotically, for you other geek engineers like me). It seems there is some incongruity with the initial mathematical procedure. I had to set the Scangauge to the mpg indicator rather than reality though. That meant it was set 4.3% higher than actual, so will have to get that adjusted next time in to the shop though.
The bad news is that the average speed was between 70 and 75 mph, and the actual mileage was 26.7 mpg. Based on past experience of over 200 kmiles, my 2004 Corolla, purchased new, would have made 34 +/- 2 mpg. The Corolla (5sp) was 2008 renormed at 36 mpg highway, also.
Looks like Subaru optimized the engine and gearing to maximize mpg during the EPA test cycle, and ignored reality...
If you put 36mpg as the HWY number in the MPG for Speed calculator and look at the numbers shown, 27.7 shows up at 75mph. Pretty close to what you are achieving.
You can achieve the EPA numbers, but not if your average speed is 70mph+
Is your complaint that the EPA numbers for the Impreza are misleading, or that your driving style does not achieve them?