Question: how accurate are car trip computers?
Answer: On average, the BMW's trip computer reported mileage 1.4 mpg higher—nearly 6 percent better—than calculated. ... Over 1064 miles, the Sportage achieved 24.6 mpg according to pump and odometer readings. However, its trip computer padded that figure by 1.1 mpg to 25.7—a 4.5-percent inflation.