broski499: full points for monitoring your trip MPG, but it's a case of apples & oranges.
There must have been different factors on each leg of the trip affecting the results - traffic, wind, elevation change, temperature etc.
If you graphed bi-directional runs (to cancel wind/grade effects) and with no other traffic around, you'd find that MPG at 55 MPH is going to be a little better than at 60.
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