Originally Posted by bullwinkle
Originally Posted by CR94
... For example, my car consistently gets 0.945 [See correction below.] times the mpg it claims as a long-term average, regardless of conditions that make mpg vary from tank to tank. In other words, it claims to burn 0.945 times as much fuel as it actually does. Toyota lies to that extent.
Not exactly right, you mean it burns 1.058 times the fuel, which is 5.8% more fuel, and I bet your speedometer (& likely odometer) are also a percent or 2 on the high side, which also means you're actually not going as far as indicated for the same amount of gas.
Not exactly right. "Burns 1.058 times the fuel [claimed]" (your wording) means the same as "claims to burn 0.945 times as much as it actually does" (my original wording). However, I did give the wrong factor. It's not 0.945, but about 0.955 (sometimes 0.956). This deliberate fudge factor on MPG displays is something manufacturers choose---subject to normal manufacturing tolerances, of course.
Your speculation about my odometer is inaccurate. It runs near perfect now. It showed slightly low with the previous tires (of the same nominal size). The speedometer indicates around 1 or 2% (hard to determine exactly with such low-resolution displays) on the high side at middling speeds, so your guess is closer there. Nearly all speedometers exaggerate by design, many worse than this.
My ScanGauge shows the speed the computer "thinks" is actual speed, based on wheel rpm and tire dimensions assumed by the programmers. That's always lower than the intentionally exaggerated speed shown by the speedometer. Both are dependent on tire size. GPS, which is unaffected by tire variations, shows actual speed to be in between the other two opinions.
