calculated vs. computer MPG - Please post your results

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When you get a chance, reset a trip meter along side a mile marker on a long segment, say 50+ miles. At the end, record the trip meter distance and mile marker. Alternatively, compare a GPS distance reading with a reset trip meter. What I've found is the distance reported by the car is off by 5-6%.

To solve the problem, I put over-sized tires whose revs/mile gave me an accurate trip meter, odometer, and MPG.

Bob Wilson

 

What size did you end up using?

 

Here you go:

How to improve gas mileage in this situation? | Page 2 | PriusChat

Yokohama P205/70R15 (787 revs/mile)

Bob Wilson

 

I'm finding 2-4 MPG off from Computer to hand calculations (Computer being higher by 2 to 4)

 

My Gen 4 is about 4-5% off (MFD is optimistic wrt reality). This has improved from Gen 3 which was 6-7% off.

 

I somehow missed the notification of your response nearly a year ago so here's a very belated THANKS!

 

My first full tank fill up:

Display readout: 51.2 mpg
Actual calculated: 47.6 mpg

 

My first tank on my new to me, 1 owner CPO 2013:

Display: 46.7
Calculated: 44.3

Still light years better than my gas Jetta

 

Funny. I sold my 2001 Jetta to get my 2013 Prius. I always get around 41 mpg. I don't know how you guys get your 45s. My car does have 16inch wheels. So the calculated is probably in the 30s. What a disappointment.

 

There's a one week average on economy mode from my unscientific test.

 

When I first got my 2012 in 2013, I calculated the difference between displayed and calculated for the first few months. Based on probably 5-6 months of data, I found that the displayed was typically 3-4 MPG more optimistic than the actual. That was mainly during the spring/summer months, and my MPG were in the high 50s/low 60s. My rule of thumb is to subtract 3 mpg from the displayed value. I always keep the car in economy mode. When I need additional power, I just mash the gas peddle.

 

After over 1,000 gallons of gas, 125+ fill-ups, and 55,000 miles, my lifetime display averages to 53.7 mpg while my calculated lifetime average is 52.04 mpg.

A difference of 1.66 mpg.

 

Edit: Removed since the .pdf file was unreadable!
3rd attempt:

 

^ A difference of about 3.2%.


For a similar data point:

3393 liters (135 fill ups, typically with just under 1/2 tank remaining), and 68,817 kms, works out to 4.93 liters per 100 km (47.7 miles per US gallon).

My average displayed fuel economy is 4.60 liters per 100 km (51.1 miles per US gallon).

The variation there is 7.2%.

There's maybe a bit of apples/oranges there: the first value is a single calculation, using the total fuel and total distance, whereas with the second all I can do is average all the displays. But I don't think it matters much.

 

I may have posted this before, but my lifetime average is 45.5 mpg, and the "average" of all my percent error calculated (each tank) is 6.4% (computer always reads high).

 

My Prius is not used as a daily driver, so in nearly three months of ownership I've put less than 1,000 miles on it. This is about my first fillup.
Miles: 475.9
US gallons: 8.251
MPG: 57.7 (calculated), 60.8 (display), 5.37% difference.
Actually, the real mpg should probably be higher than that, because I wasn't quite sure that the tank was full when I got the first click, so I squeezed more into it until I got the second click. Now I know that the filler "neck" holds a quarter of a gallon. Using the figure of 8.0 gallons, my mpg would be 59.5. I think that is acceptable fuel economy for the first tankful in my first Prius .

 

Another tank or two, and any disparities in your fill technique will cancel out. That's very good mileage, you must be consolidating trips.

 

"Another tank or two, and any disparities in your fill technique will cancel out. That's very good mileage, you must be consolidating trips."

Yes, since I have the convenience of another car for daily abuse, I can choose to drive the Prius on trips of at least 10 miles, or on strings of short runs. I try to drive it at least once every 10 days or so, and I always find reasons to visit family and friends in other towns. This is my first Prius, but I did put close to 300 thousand miles on an Insight. I discovered that over the years I had worked out for myself various driving techniques for fuel efficiency, usually by trial and error and by watching the real time MPG display, though I try to never hold up traffic. I'm sure I still have a lot to learn. Since the weather affects fuel use - quite a bit - I'm curious about what will happen this fall.

 

Since my first fill up in the PiP on January 15 this year, my calculated raw mpg averages 89.71 mpg vs. the HSI display guesstimate of 94.71. So it's about 5.6% optimistic. That covers 11,984 miles.

 

Consider getting a smart charger, and maybe install a quick connect for it. Our usage is not that sporadic, but I keep it on such a charger, whenever there's a day or three idle time.