Quote:
Originally Posted by cyclopathic
I punched the numbers into recommended calculator 2800lbs, ,28 Cd, .31 engine, .92 transmission efficiency, etc and calculator shows 53 at 65 and 42 at 75. Test snows 53 at 65 and 38 at 75 consumption. Calculated drop is 21% and actual is 28%, 1/3 worse.
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MPG is not linear, and the actual rate of consumption over a set distance must be used. The calculated drops are much worse than you realize.
For example, a drop of 5 MPG is meaningless without knowing what the start and end MPGs are. A 5 MPG change from 25 MPG to 20 MPG is an increase of 1 gallon of gas per 100 miles (A change from 4 to 5 gallons = 25%). Another 5 MPG change from 10 MPG to 5 MPG is an increase of 10 gallons of gas per 100 miles (A change from 10 to 20 gallons = 100%).
For your numbers:
53 MPG drop to 42 MPG increases fuel consumption by 0.494 gallons per 100 miles (26%)
53 MPG drop to 38 MPG increases fuel consumption by 0.745 gallons per 100 miles (39%)
Gallons per 100 miles = 100 / MPG
53 MPG = 1.887g /100m
42 MPG = 2.381g /100m
38 MPG = 2.632g /100m