Mileage vs mileage comparison between the app and my car's odometer

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My Honda CRV's display constantly shows a total mileage that is different than my Automatic mileage for the same trip. The difference is small, but why is there any at all?
Do you read a different source for actual miles driven than the car's dash display?

Thanks again!
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Stanley Rowin

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Posted 3 years ago

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Matthew Stevens

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The mileage has never matched on my Prius C either: not even close most of the time.
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Tom, Former Employee

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Good question, Stanley. The app determines distance travelled by reading velocity data directly from your car's on-board computer, so it's not direct "copy" of your car's dashboard display (which likely displays odometer data). Odometer data isn’t available via the OBD-II port, which is why we look at other data sets to determine distance traveled.
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Robert Reuscher

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There can be a number of reasons why the mileage is different, but it should be close on a single trip unless it's long trip. 

1) does your odometer show tenths of a mile? Mine doesn't unless it's on the trip odometer. 

2) Have you replaced your tires? Did you put the same exact model of tire back on your car? The odometer/speedometer in your car measure tire revolutions for distance and speed. They are calibrated for the specific size tire, and probably for the original tire delivered with your vehicle.

For example, my charger takes 235/55-R18 tires. It came with Michelin Pilot MXM4 tires, I replaced them with Goodyear Assurance Comfortred. Both are the "same" size (235/55-R18), but the Michelin tires rotate 731 times per mile and the Goodyear's 744 times per mile, this has thrown off my speedometer by about 1 mile per hour. This is also going to make my odometer off too. It's because the Michelins outside diameter is 28.4", the Goodyears are only 28.1 (even though their tread depth in 2/32 deeper). 
3) Plus I sure the car's odometer has a specified accuracy rating, I doubt that any of them are 100 % accurate that's put in a mass production car. 
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On a 2015 Honda Accord Hybrid, the mileage shown in Automatic is consistently 5-10 MPG higher than the dashboard shows.

I get really good gas mileage (the car states 67.8 MPG on the current tank and I know it to be accurate because I take it right down to 0.2 L or so and fill up to the tippy top which is 18.875 gal every fill up) but the Automatic adapter has consistently been at 74.5 - 76.4 MPG per week.  I'd love to get that kind of mileage, but it's simply not accurate.

As a suggestion, it would be really nice if you could add a user customizable field for tuning mileage error up or down by a percentage and/or MPG.  In my case, I would tune down by 11-12% and my Automatic would be reporting data far more indicative of the true MPG that I get out of my vehicle.

As an aside, I think the margin of error comes from the fact that I get poor (16-35 MPG) in the first few minutes of driving due to how the current Honda hybrid system works (warming up the gas engine from cold start, etc) vs after driving for 20, 30, 40 minutes.  Using the third party DashCommand app in conjunction with my 2nd gen Automatic adapter, I'm able to see that I can get upwards of 90 MPG on the 35-45 mph streets that make up the end of most of my trips.  I think the difference in MPG between trip start and trip finish makes the Automatic adapter's view of my MPG skewed so high.
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Tom, Former Employee

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Thanks for the really detailed post, siobhan. As Ani explains in this related topic, since hybrids have a part time EV only mode, this can cause some of our MPG calculations to be off for certain models. Here’s a link to a related topic on inaccurate MPGs as well. 

It sounds like this has been a consistent problem for you, so could you send a message to about this? Our tech support team will review your drive data in more detail.

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