Solo long distant driving offers plenty of time for serious contemplation on the finer points of MPG and Mileage Computers/Odometer readings...




so once while cruising across five states in six days, I began the simple task of doing an odometer check by synchronizing the speedometer/odometer with the highway mileage markers - fully expecting them to be consistent with each other.


Well, things were invariably consistent from the very start, but anything but accurate...

Strangely, the Bullitt's odometer was showing me that it was under reporting the actual mileage by approx 0.1 every ten miles!!! [ or 1 mile in every 100 miles traveled ]

This data remained absolutely true over the entire 2500 mile trip and I am 100% confident that there is no simple explanation [yes, I'm still on the OEM tires].

now here's the question for the experts here; given these facts, was the 27.2 MPG - as calculated by the Mustang's computer - being too generious, or was it under reporting the Bullit's true MPG?

I welcome your on-topic comments please ...

 

1% on the odometer isn't too bad, and based on that your 27.2 is really closer to 27.5, but check the "Gallons used" on the next fill. On mine it under-reports the fuel used by close to 5%, and the actual fuel mileage is overstated on the computer by that amount. If yours is similar, then your actual mileage is closer to 26.0 mpg.

I returned home from a trip this week in my GT and showed 28.2 for the 610 miles. That is closer to 27 in reality.

=Vic=

 

hmm, I wouldn't call 1% "serious".
You must reset regularly for real time consumption.

 

You are also taking for granted that the mileage markers have no inaccuracies in their placement.

 

I agree with hawgman. Coupled with that, your sense of timing isn't perfect, so you might not be syncing at the exact same times with the start and end mile markers as you pass them at highway speed. (and technically the more miles you put on your stock tires, the smaller they get and the higher speedometer and odometer readings you'll get, but that's an extreme case)

I did an experiment over the summer to figure out why our speedometer needles are inaccurate. It's been my experience that the needle never matches the actual speed you're going. It's usually 3 mph faster (reads 75 when you're really doing 72). And a lot of people have complained it doesn't match their GPS. If you hook up an SCT tuner for data logging, like I did, you'll find that the speed the car tells you you're going is different from what the computer actually knows (shown in the data logging). And the one the car knows (VEHICLE_SPEED) is dead on with the GPS (I used two seperate GPS devices simultaneously to confirm).

Now I trust my odometer more than the mile markers.

 

I have noticed this aswell. but I thought the road crews here in AZ were ummm