calculated vs. computer MPG - Please post your results

Over a little more than 5000 miles I'm averaging 47.5 and my car displayed MPG is averaging 50.1. A bit disappointing since my 2005 was less than .5 MPG in error. My gas mileage has improved significantly over the last few tanks, getting broken in and lots more air in the tires. My last four fills were 51.3, 47.2, 49.8 and 48.4 actual MPG. This is going up and down 3500 feet each day. The extra power is very nice.

One last note my 2005 averaged about 43 MPG on the same route with Ethanol fuel, 46 with real gas. Can't find real gas here anymore so I think the 2010 is a significant improvement.

 

What I wrote was 5% from Toyota engineer and 10% from VW Golf.

Ken@Japan

 

My mistake! Happily, this matches the latest calibration trend line:


Thank you Ken!

Bob Wilson

 

My Gen III is now at its 60 day mark. The first tank was spot on with calculated amounts but every tank since then has been about 3 miles less then what the computer reads (ie: computer reads 62 by i calculate closer to 59).Hopefully they can update the software!

 

First fill after 500 Km on her and still breaking it in...56 MPG imperial or 46.5 US MPG...display says 4.9 KM/100L

 

I just filled the tank the second time so the first two fills have given 53.5 amd 54, respectively, for computed MPG vs 55.5 and 56.3 MPG for the dispalyed data.

 

Now reporting in with 15 tank fills. I see some regular fluctuation, though this recent tank was very close to the overall average difference between the MID's Computer MPG and my Per-Purchase Calculated Mileage.

I continue to see the 2010's MID computer exhibit a fuel economy at right about 5% above the MPGs I calculate after each purchase.

Here is the latest update of my chart for the first 7,000 miles on my 2010:


See the following link for a higher-resolution graph:
View attachment 2010 Prius Mileage Record 7081 Chart.pdf

 

Just filled up again today and the car computer said 59.2, at 40mph average. Actual was 8.9 gallons for 503 miles or 56.4mpg. It seems that the higher my car computer reads the larger the difference from the calculated mpg.

 

Thanks! I can add this to the 'mph vs MPG' chart. As for the error:

59.2 * .95 = 56.24 corrected indicated
(56.4-56.24) / 56.4 ~= .3% error
​

Bob Wilson

 

I am not sure if Bob still collects data, but here some data from my collection. Four tanks. The second set seems skewed... perhaps not completely filled the tank... who knows. All this time I have mostly daily trip to work about 50 mil round-trip into New York City and home. Average speed 16mph (that is consistent for the lifetime) not much elevation difference guess the biggest the bridge !!!.

I used to have a GenII and after a few hand calculation in the beginning I never bothered just trusted the computer... so I am little disappointed with this large (5%) reported difference. By the way how this error is calculated ?? What is the base the reported vs. calculated (if makes any difference)?

	Column 1	Column 2	Column 3	Column 4
0	miles	gal	mpg indicated	mpg calculated
1	458.5	9.39	49	48.84
2	532.4	9.05	58.2	58.83
3	493.5	8.99	57.7	54.89
4	490.7	9.22	56.2	53.24

Gabor

 

2nd fillup (11.541 gallons):

Miles Computer MPG Actual MPG (hand calc) Avg. speed

701.2 64.1 60.8 25

 

Thanks and this is good data for the calibration study but we have enough, over 130 samples. What I need now is:

	Column 1	Column 2	Column 3
0	mpg indicated	mpg calculated(optional)	average mph
1	xxx	yyy	zzz

.
I'm adding samples to an 'mph vs MPG' chart. Over time, we'll see trend lines that will allow us to understand what this car does in the hands of multiple drivers in different conditions. We'll get a 'range' of results.

Right now, I'm not too worried about PnG versus cruise control or other driving styles. Driving style is not a 'population' study but needs a specific "A" vs "B" vs "A" testing. However, a population study is very useful for understanding the vehicle as individual drivers 'average out' and we'll have the ZVW30 numbers.

Bob Wilson

 

Bob,

You can use my data to start. Interestingly all of those were at 16mph average. Really. Not too surprising, since I really used the car on the same exact route 5 times a week and very little else. (Had no vacation this summer). That means about 8-9 trips plus a little in town driving per tank.

Will create the table you asked above in my next posting.

Gabor

 

Bob asked data in this format

	Column 1	Column 2	Column 3
0	mpg indicated	mpg calculated	average mph
1	49	48.84	16
2	58.2	58.83	16
3	57.7	54.89	16
4	56.2	53.24	16

Hope this is helpfull.

Gabor

 

	Column 1	Column 2	Column 3
0	mpg indicated	mpg calculated	average mph
1	54.5	52.11	31

This is with increasing the tire pressure to 42/40 about half way through. The total miles driven for the above is 487.9 miles.

 

I've just updated the chart and here is what we're seeing:


Also, I didn't realize we have a peak, trip meter:


Bob Wilson

 

I've got a chart like that for my 15 tanks, and it just isn't enough for me to develop any trend.

I can't recall whether you have my MPG v. MPH data, Bob. Here's what I have to date:

	Column 1	Column 2	Column 3
0	MILES	MPGs	MPH
1	463.3	57.6	25
2	460.3	57.7	50
3	564.4	51.7	48
4	547.9	59.3	27
5	518.0	57.3	21
6	484.5	50.7	44
7	420.4	60.4	40
8	318.4	59.0	35
9	406.6	59.2	28
10	503.8	61.3	26
11	462.0	58.8	28
12	286.4	57.8	35
13	355.6	52.7	55
14	494.4	59.0	26
15	483.0	54.0	20

View attachment MPGvMPH_7081.pdf

 

I think constant speed MPH vs MPG relations are reasonable research item.
But, I think variable speed tank average speed MPH vs MPG is meaningless.
It's just my personal opinion.

Ken@Japan

 

If the driving style varies considerably during the measured period, I would agree.

I keep track of the mileage by "style" -- city and then highway. Really, though, I track it by urban and inter-urban. I think that data may have more value.

 

For a vehicle performance benchmark, I agree that constant speed, 'mph vs MPG' is critical for modeling. I'm keeping that chart separate from the general user reports. There is a concept called "managing user expectations" and that is what the second chart does.

Many of us have seen postings complaining about not getting the expected MPG. These invariably fall into groups or combinations:

• speed - those who feel they must drive +80 mph (130 km/h)
• short trips - trips of 5 miles / 8 km or less
• untuned - over filled oil, under filled tires, alignment
• sub-optimal driving - taking the high-speed, steep hill in the morning instead of route that allows vehicle warm-up or use the traction battery to arrive

These self-selected, user reports are giving us a clue, a hint, that this vehicle easily achieves 50 MPG (4.7 l/100 km) or better out to 70 mph (112 km/h) and then it starts to fall off. This is the new 'knee in the curve.' It also shows higher performance is possible within the PriusChat pool of drivers. We are learning what works and this after having the car in our hands for less than 120 days.

I'd also note that:

12 gallons @ 85 mph = 1,020 miles
​

Off hand, a 1,000 mile tank, as Ken@Japan has already shown, is well within the vehicle's capabilities.

Bob Wilson