calculated vs. computer MPG - Please post your results

what???? there goes the trade in value on your pip!

 

Or you could look at it as the more he drives the closer he gets to owning a pip!

 

Trip A / miles 9,423.3
Avg. Speed indicated / 40 MPH
Indicated MPG / 55.4
Calculated MPG / 52.868
Difference / -2.532 mpg
Gal's used / 178.241
Gas/ Reg with 10% Ethanol
Tires / for the first 7,000 + miles / Michelin Energy Saver Tires AS/ 195x65x15 w/ 44 psi in all 4 tires.
for the last miles / Bridgestone / Ecopia / EP422 / 195x65x15 / 44 psi in all 4 tires

 

Out of 10 tanks I've kept track of displayed MPG 4 times:

Code:

#    MPG(c) MPG(d) Chg.(%) Chg.(#)
1    49.8  52.2    +4.82   +2.4
2    51.4  53.0    +3.11   +1.6
3    49.2  52.8    +7.32   +3.6
4    48.6  49.2    +1.23   +0.6
-----------------------
AVG. 49.6  51.7    +4.15   2.1

 

My computer vs. hand mpg has been remarkably stable, even though there was a recent 1500 or so mile gap where neither my wife nor I were driving the car. Trip B, which has not been reset since the car was new, has 49.5 mpg over the 46.8K or so life of the car. My hand calc., for everything except the 210 miles before we bought it and the about 1500 miles while we were away this spring, has been about 2.4 mpg less for most of the life of the car, and now stands at 47.1.
I expect that to go down just a little bit due to new tires.

 

About 5.1% difference. A little lower than mine, but very consistent with other drivers, I believe. I think mine may be higher due to the RPM of my 215/45R17 tires.

 

Trip A (continuation without being reset) Miles 10,388.6
Speed Indicated: 40 MPH
MPG Indicated: 55.4
MPG Calculated: 52.886
Gals: 196.388
Gas. Reg. 10% Ethanol
Tires: 195x65x15 Bridgestone Ecopia EP-422 / 44 psi in all 4 tires( for the last 3,000 miles) before
that Michelin Energy Saver AS same size and PSI.
Difference in Indicated vs Calculated MPG = 2.514 mpg

 

I live in San Diego, so the weather is pretty moderate year round. I have a Jan 2012 Prius. I have an issue where I can never get 10 gallons into the car even though it is supposed to be 11.9 MPG. I can see some reserve, but not over 2 gallons. If I go past the 0 miles left on the tank (15+) I can get almost 10, but I have never been able to put in 10 gallons. Since I get less than 10 gallons, it is pretty easy to calculate the mileage in your head by taking the trip set odometer reading and then dividing by 10. I am consistently getting 3-5 mpgs less than the consumption calculation provided by the car's computer (always less, so if the computer averaged, the millage should range above and below the actual calculated number at the pump). On the last tank, I went 455.8 miles on the tank, and filled up with 9.9 gallons, or 46 mpg. the consumption number on the car was 49.1. This is one of the closer ones. To me this is a problem. I believe the tank should be able to be filled with about 11 gallons (some reserve) and my mileage should be close to 50 (I do drive to get the better millage). I do not believe the car is meeting the specifications that they are selling it to, and would have expected over 500 miles to a tank. As I assume from this forum, people who do not believe the computer, and do the math at the gas station, they are not getting the promised millage. Anyone pushing this issue?

 

You can go a fair amount past the "0" mark, but do so at your own risk. fwiw I've done 70 miles past the 0.

Yes you will average about 5% less real life consumption compared to the car's computer.

As far as getting better gas mileage, you've came to the right place. Have you read many thread or watched any videos on how to pulse and glide?

 

Welcome to PriusChat, Larry!

I don't know that the size of the gas tank has been an issue for anyone, unless the driver needs to be driving more than 500 gallons without stopping for gas. You can drive farther, though I wouldn't recommend it.

Of 293 cars reporting 1.4 million miles of driving with the 2012 Prius, the average fuel economy is 49.4 pounds. You do not have to meet or exceed this, but if you have mileage significantly below this figure, then it would be a good idea to evaluate your driving routine. Here are a few questions that could help people understand your situation and, if possible, offer suggestions on how to improve your mileage:

1. How many miles to drive each day? Do you have a regular commute?
2. Are you driving on highways or city streets?
3. What speed do you drive?
4. Are you driving to try to use the battery only?
5. Do you know the pressure in your tires?
6. Have you made any alterations to your Prius?
7. Do you normally have many passengers or carry anything else in the car when you drive?
8. Do you have the A/C on Auto? At a specific temp?
9. You wrote that you drive to get better mileage: Can you describe how you drive?

Your answers are not going to be right or wrong. They may just help other people understand your situation.

 

So many variables, so much room for improvement!

To me number 5 is the easiest to control and is directly proportional to better mileage.

 

I reset the trip computer every time at the pump, and calculate my own MPG. My own number is always 2.5-3 short than the MPG provided by the onboard computer. Like once I reached 60.1MPG according to onboard display, but my calculated number is only 57.5

I'm kind-of suspecting that Toyota is tweaking the odometer a little bit so that the recorded "1 mile" is shorter than the actual "1 mile".

Once I was taking a 150 mile trip into PA, I use my GPS to record the trip, as well as my iPhone. I do see about 1.5-2 miles difference between the odometer readings and GPS records -- not sure this is due to the "standard deviation" or it's a deliberately manipulating of the system so that it will give us Prius owner something to brag about to others... hope not...

 

I broke my record just now for best tank. With the cooler weather approaching hope to get even better tanks.

10/09/12

Miles: 618.2
Gallons Pumped: 10.578
MFD = 62.0 mpg
Calculated = 58.4 mpg
Error -3.6 / 5.8%
Avg Speed: 27 mph

 

Congratulations! Around these parts, the cooler weather (meaning overnight freezes) makes it more difficult to get such fuel economy. I'm very pleased to be working on a tank that is showing 58.5 MPG (at 525 miles), and I know I won't see this again until April/May.

 

Our mileage experience after 45,000 is the same. There is about a 2 - 3 mpg less actual than what the computer shows. This experience is well documented as we record actual mpg after each fill-up.

 

I also would like to note that we witnessed a significant decline in our mpg (normal during times at home with travel to work 5 days a week runs anywhere between 52 and 55 mpg) after putting Yokohama tires on a couple of weeks ago. Our last two tanks were calculated at 48 mpg. I added some air to the tires but will have to wait and see what the result is this weekend. Very disappointed in the new tires but will admit that the original tires were pumped up a wee bit maybe 35 lbs or slightly better.

 

I very strongly doubt that Toyota is tweaking the odometer this way. It would be rolling out the red carpet for the class action lawyers who have already extracted settlements for warranty fraud on two different brands of my older cars, even though neither of mine actually had that bias.

My current and previous Prius have odometer errors of only 0.1-0.3%, both in the other direction, as compared to my GPS measurements (after discounting a GPS problem, below) and to DOT highway survey markers.

My hiking GPS, when operating in Battery Saver mode, shows a significant disagreement with the odometer. It gets worse in the mountains. But in continuous mode, it agrees very well with my automotive GPS. And both agree well the DOT markers over very long stretches that don't contain milepost discontinuities, down to the 0.1% level.

 

Thanks!

The summers are tough in Phoenix and AC is a must. The winters are mild here. The coldest it gets is high 30s for the low which usually only happens late December.
Ive never hypermiled in the winter, I assume your winters would be a lot harder to obtain good mpg than summers here in phoenix using constant AC.

 

You've got that right!

Have you ever had an entire tank below 40 MPG? It's happened to me, and it is a direct result of single digit temps. Even longer drives don't turn out that well as the extremely cold air just sucks the heat out of the aluminum block. The A/C will take its toll, but the cold does much more to drop the MPGs. I takes a lot of power to run the A/C, but it takes a fair amount to move enough warm air into the cabin -- and then you also have to deal with the effect of cold on the ICE performance.