calculated vs. computer MPG - Please post your results

Trip A : 5,111.5 Miles
Average Speed: 40 MPH
Indicated MPG: 54.6
Calculated MPG: 52.289
Gal's used: 97.753
Gas Type: Regular unleaded various brands Costco etc. with 10% Ethanol

Just filled up and the computer indicated 57.7 MPG when real MPG was 54 MPG. Off by about 6.5%.

GPS will tell you! I have a 2010 III with 40K miles. I noticed the mgp always about 3 % lower than the calculations at fillup. Then I noticed my gps shows me going 57mph and the prius shows 60mph on the highway. I imagine you'd have to check other gps' to see if the prius does really read the mph high. Obviously if it does...there's your error cause. Yes, I have the stock tires. What do you get on a gps for compared speed?

The car computer reads correctly despite the speedo being off by 2mph on average. Others have checked odometer accuracy via highway mile markers and the odo appears accurate.

07/20/2012
Miles: 702.5
Gallons Pumped: 10.171
MFD = 71.7mpg
Calculated = 69.1
MFD vs. Calculated = -2.6
% Error = 3.8%
Avg Speed: 37mph
Price: $3.599

Trip A / several fillups
Miles: 6,136.1
Indicated MPG: 55.3
Calculated MPG: 52.863
Error: 2.437 mpg
Gals' used: 116.074
Avg. speed indicated: 40 MPH
Gas: regular unleaded with 10 % Ethanol (mostly Costco brand)
Tires: 195x65x15 Michelin Energy Saver AS tires with 44 PSI
max sidewall pressure in all four tires.

In theory and I believe in fact, the more miles you have and fillups
the more accurate you will be on your figures when comparing
indicated MPG's with calculated MPG's.

Trip A (several fillups) without resetting
Miles: 6417.7
Avg. speed indicated: 40 MPH
Indicated MPG: 55.5
Calculated MPG: 53.0792
Difference: 2.421

Gas: regular unleaded with 10 % Ethanol (mostly Costco brand)

Tires: 195x65x15 Michelin Energy Saver AS tires with 44 PSI

max sidewall pressure in all four tires.

Last tank, filled up 07/28

600.2 miles
10.38 gallons
Dash reading 61.2 mpg/manual calc 57.8 mpg = 5.5% error
Average speed 30 mph
Constant AC use 75/76 F one to two bar manual setting.

Hopefully you guys can shed some light on what I'm experiencing. Just bought a package 5 about a month ago. Right now on my current tank the car is showing only 43 mpg! I used trip A to see this info. On trip B (which hasn't been reset since I bought the car) I'm getting 45 mpg. My trips are mostly round trip to work which is about 16 miles. That round trip is about 30% stop and go residential and 70% longer stretches of city driving. I'm almost always in Eco mode and I'm trying my best to apply all the driving techniques I've read about here. There are only 650 total miles on the car so I'm wondering if it's a break in thing? Would appreciate any light being shed on my poor (comparatively) mileage.

This really isn't the place for this question but yes, it's a break in thing as well a a 17" wheel thing and a new-to-a-GenIII thing. all of these combined along with semi-short trips can ding mpg. With decently long trips and some effort you may be able to get into the 50s but a lot of folks average mid-high 40s with 17" wheels unless they have a killer commute, drive slow, hypermile or use 100% gasoline. I would expect your mpg to go up once you figure out the nuances of this car and the tires/car breaks in.

Oops. My apologies for posting in the incorrect thread. Should I start a new thread?

Trip A (several fillups) without resetting
Miles: 7826.1
Avg. speed indicated: 40 MPH
Indicated MPG: 56.2
Calculated: 53.714
gals. 145.699
2.486 difference
Gas: regular unleaded with 10 % Ethanol (mostly Costco brand)
Tires: 195x65x15 Michelin Energy Saver AS tires with 44 PSI
max sidewall pressure in all four tires.


Read more: http://priuschat.com/threads/calculated-vs-computer-mpg-please-post-your-results.65053/page-43#ixzz22sHm6iAA

Miles: 700.2
Gallons Pumped: 10.141
MFD = 72.4 mpg
Calculated = 69.0
MFD vs. Calculated = -3.4
% Error = 4.63%
Avg Speed: 23 mph
Price: $3.73

523.4 miles
9.46 gallons
58.9 mpg dash reading = 6.1% error
55.3 mpg calculated
29 Avg Speed
3.29 a gallon
Constant AC use
Stock 15 inch tires - 42/40

Mark and Kalome, those are nice tanks. Congrats!

Why thank you, but not as good as your numbers.

I just posted a thread. I would be interested to know how you have yours setup on your Gen III.
Mounting your scangauge | PriusChat

Thanks man!

Off topic, but has there always been this many crazy anti-good-gas-mileage people on this forum? Some of those other threads are nuts.

Everyone's situation is unique so I try to take that into consideration when judging someone's mpg numbers. I know what you are dealing with temperature wise and I think you are doing well so I have to say something. My average numbers are only 64-67mpg indicated because of my uphill commute and higher speeds. If I moved back to my old house my numbers would drop quite a bit.

Your ability to pop off 70mpg+ tanks left and right makes me jealous!

The sudden influx of anti-hypermilers is nothing new. When a new model of Prius comes out we see a lot of new members who traded in sports cars for a Prius. They continue to carry their old justifications for speeding and their anger for those who would rather driver slower. I find it amusing that just because they came over from an Acura TL or a BMW We are supposed to be impressed or that maybe they are the better drivers or more courteous because they speed. *rolls eyes*