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Here is one. My Porsche has a display which tells you the MPG. However the car display is consistently between 1 and 2 mpg better than what I calculate after fi

by larrys 11y ago

Here is one. My Porsche has a display which tells you the MPG. However the car display is consistently between 1 and 2 mpg better than what I calculate after filling the tank and doing the math. And I repeat it's consistently worse than the display which calculates the mgp per tankful which is probably what most people rely on. I've been meaning to bring this up with the dealer but haven't so far. This is in addition to not coming anywhere near to the stated MPG and with conservative driving (non sport mode ..)

rconti 11y ago
Yeah, mileage computers in cars are known for being a bit optimistic. It's not hard to beat the EPA highway number for your car. Put it on the highway, cruise at 65mph, done. The EPA test cycle doesn't even exceed 55mph, but it has quite a bit of slowing and speeding up, so you can beat it with a consistent cruise a good bit over their 55mph number.
- ptaipale 11y ago
  A partial reason for this is that the speedometers have to be optimistic by law (depending on jurisdiction, but I think this is the case most everywhere. When your speedometer shows 100 km/h, it is permitted that true speed is 90 km/h, but it is not permitted that the true speed is 101 km/h. And the same variance applies to odometer, of course. Things like tyre wear and pressure have a noticeable impact on what both meters show, and manufactures have to stay on the safe side, by law.
  - rconti 11y ago
    This is true -- my understanding is that Germany actually requires they never read low EVEN IF FITTED WITH THE WRONG SIZE TIRES which is sort of insane. That said, I believe the odometers are typically bang on, which would mean the mileage calculation should be accurate. Or could be, if they wanted it to be.