my evic is usualy within 1/2 mpg of actual pretty consistantly, now that i have my 245/75-r16 BFG MTKM tires.
The evic was off by a bunch (always over est fuel econ) b4 i put the bigger tires on.
My speedo is now dead on (where b4 the tire upgrade, my spedo read faster than acutal speed) my odometer is off by about 11%. when i put my 11% back in after getting the "fill" mileage, it almost always agrees w/ the EVIC within a 1/2mpg ish.
Sample data from my fillups
10/13/2007@036788
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Fill ((410miles)+ (41.0miles)/19.6gal) == 23.01mpg
EVIC == 23.4mpg
SG == 19.5mpg
the 41miles is adding 10% of the miles back in for the odo being off (bigger tires will make your odo read too low, which is y most people complain a lift makes their mpg go low, yes yes aerodynamics axle ratios ect blah blah blah, but most of the time, they just dont factor the tire diameter).
SG is low b/c it crashes all the time and is never right