calculated vs. computer MPG - Please post your results

After that long beep and the "2 go" miles @ 0, I know the co-pilot will keep leaning over and looking at the dash until I stop and fill up, even though I feel confident that another 75 is a very safe estimate. It's a losing battle.

 

That is incredibly helpful, thanks so much. What is the diff between CONS and AVG? The avg given was 34.

BTW- I'm sitting in the prius with my a/c...dont want to get out of the car- its so hot out! Like most people in this area, I dont have a/c at home.

 

Avg should be speed in MPH

 

Thanks for that Link priori, With that in mind Im prob getting about 61 mpg, Ill check when I fill back up.

 

all that I can say is I run 2mpg less that what the car says in true calculations but sometimes it is right on, I am sure it will very based on the pump kicks off.

 

I've been running 6% oversized tires in our NHW11 and also recently completed a 1,000 mile tank with my wife's ZVW30. From these experiments, I've traced our errors to the tire diameter:

indicated_miles / indicated_MPG = true_gallons​

Our ZVW30 has Sumitomo T4s that using GPS calibration are less than 1% off. The indicated and measured MPG are accurate. As for our NHW11, the oversized tires completely account for the indicated MPG error.

In the case of the NHW11, the indicated MPG is always lower than true. But the lower transmission speed, the tires turn slower at any given speed and this improves real MPG.

Bob Wilson

 

Date Aug. 11, 2013
Miles driven: 344.5
gal's used: 6.140
mpg computer: 58.3
mpg calculated: 56.107
difference: 2.193 mpg
speed avg. 44 mpg
25 % city / 75 % hwy: speed range 25-72 mph (freeway driving Interstate 5 Washington State).
Gas used: Costco / 87 reg unleaded with ethanol
tires 195x65x15 Michelin Energy Saver AS (all inflated to max sidewall pressure 44 psi)
Note: Energy Saver tires increased mpg at least 2-3 mpg over stock Yokohama Avid tires.

 

Hi F8L - My last two fill ups on our new 2013 Prius results were:

Manual calculations using "Mileage Tracker" 53.150 mpg compared to computer which said 54.6
Manual calculations using "Mileage Tracker" 50.920 mpg compared to computer which said 53.4

So computer had an extra 1.45mpg on one fill and 2.48 more mpg on the other. So while the computer is off a little, it wasn't off a huge amount.

Manufacturer Date is April 2013

This mileage was about 50/50 city and hwy. I am very careful in my driving style, but not a hyper miler. Most miles were driver only with car empty.

We also have a 2010 Prius, I'll check the figures for that year model to see if there is any difference.

Interesting thread, , , THANKS

 

As an update my car computer is 2.6mpg optimistic every time.

Travis

 

My question is when you turn your car off, the screen gives you the time driven, miles, mpg aveerage. But it is always different then the con average on trip A or B. I know the trip is average overall but should the computer one being higher always raise the trip average?

 

2010 Prius with 17IN wheels. Computer is off always.
3 Fillups ago Computer 48 Manual 46
2 fillups ago computer 47.9 manual 50.2
last fillup Computer 43.9 manual 40.1

 

Mine is roughly 2-3 optimistic vs Fuely...I've only started using Fuely this month, however last fuel up:

Prius Said: 52.8 / Fuelly said: 49.6

 

Prius on-board trip computer: 58.8
Fuelly actual calculation: 55.9

 

Update today :

Prius: 50.1
Fuelly: 47.8

 

I have checked about 15 tank refills and find that the actual hand calculated MPG averages 2 to 3 MPG less than the car's computer shows. This is a 2012 model 4. This seems to be in the range that most owners are seeing.

 

I thought I might give this thread the benefit of some long term data. I took delivery of my 2010 Prius V on 6/2/09 and have kept track of all my gasoline purchases in a little blue book. I transferred the data to an Excel spreadsheet so I could do the math. From the very beginning, I noticed there was a difference between the way I always calculated MPG (miles traveled / gallons pumped) and the way the MID calculated MPG (Trip A display). So I started keeping track of my MID MPG starting in October of 2009. There were a few occasions where my record keeping broke down but my Odometer and Gallons pumped is complete. So here is the data:

Total Miles = 37083 Total Gallons = 859.6 MPG = 43.1

MID MPG Ave = 45.4 MPG Difference = 2.3 %MPG Difference = 5.5% ((MPG Difference / Calc MPG) * 100)

Maximum Number of Entries: n = 118

Just a few observations. Most of my driving is short trips around town. There are a lot of stop lights and stop signs. So the "pulse & glide" method works only after the engine is warmed up to normal operating temperature. My best MPG is 53.8 and I like the 5-Minute MPG bars on the MID. It is great when I can get a bar > 75 MPG.

I hope this helps keep the thread interesting.

Rich Mulligan
Hawthorne, CA

 

It seems in summer our Prius is usually off about 2.5 mpg, in winter its closer to 3.5 mpg, the gauge
always over reads the real true calculated mpg's. We now have over 106,000 miles so it is not
due to the gas pumps cut offs etc.

 

Alright wow, this thread has been going on for 4 years. Most of the reports are that the computer mpg is too high. Any idea as to when Toyota will fix this?

 

I doubt it'll ever happen. I've seen some users report success when filling to the top of the neck. Not really sure how this makes the indicated mileage and the calculated mileage differ.. Not going to try it either, haha.

Anyway, here are mine. I have a 2012 Prius C, will check on date manufactured tomorrow. Here's what I've tracked since the day I picked my car up (less 2 partial fillups including the dealership fillup and the tank following it). Feel free to take a look at my Fuelly as I keep all of my data in my notes on there. I expanded my notes so I can see everything easier and quicker too. I love Fuelly.

325.7 miles 62.9 indicated, 54.8 calculated
422.9 miles 59.3 indicated, 57.5 calculated
472.1 miles 60.9 indicated, 58.1 calculated
468.7 miles 61.2 indicated, 57.8 calculated
511.3 miles 64.5 indicated, 61.0 calculated
489.1 miles 65.0 indicated, 61.4 calculated
460.1 miles 62.3 indicated, 58.7 calculated
472.2 miles 62.4 indicated, 58.3 calculated
404.9 miles 55.2 indicated, 53.0 calculated
447.9 miles 60.1 indicated, 56.5 calculated
450.0 miles 63.7 indicated, 60.5 calculated
507.6 miles 66.5 indicated, 63.0 calculated
500.7 miles 64.6 indicated, 61.2 calculated
461.1 miles 61.6 indicated, 57.8 calculated
521.0 miles 70.4 indicated, 67.4 calculated
542.9 miles 75.4 indicated, 71.8 calculated
520.6 miles 67.9 indicated, 65.4 calculated
353.7 miles 64.5 indicated, 62.3 calculated
441.2 miles 70.7 indicated, 66.9 calculated
451.2 miles 69.8 indicated, 66.8 calculated
519.3 miles 68.6 indicated, 65.4 calculated

This translates to 64.6 indicated, 61.2 calculated (on average) and thus a generous 3.4 MPG difference over the course of around 10k miles (on average)