calculated vs. computer MPG - Please post your results

Re: 2010 calculated vs. computer MPG - a correlation

a general observation needs to be made (perhaps it has been?); the difference between the indicated and actual mpg is consistent with the discrepancy of the vehicle speed, indicated vs radar confirmed. Both our 2010 II & V are about 4% slower than indicated which is virtually consistent with the difference in the mileage...

 

First fill up

477 miles, 8.4 gallons.

Display = 59.0 mpg
Actual = 56.8 mpg

 

As the weather warms I'm again getting a calculated tank in the low 60s actually 64.4 per display, 62.3 per calculation. Display remains roughly 2 mpg higher than actual.
Tony Renier
PS If the display mpg is off, might not the speedo and odo. be off too? Then everything goes down the toilet.
Tony Renier

 

The speedo and odo ARE off - and will never be exact. Each manufacturer's tires (and different tire models) can be off a fraction of an inch from the spec size, and as they wear this will change. It changes as they warm up also. 1/6" of tread wear = 1" change in circumference (1/6" off each end of the diameter, times Pi).

Lots of variables, but it's still rather interesting that the programmers chose to make the final number always read a little high - hardly anyone has readings which are below actual.

I do find a pattern of slightly less error when most of the tank was on cruise control - and slightly more error (slightly) when doing multiple trips at varied speeds and varied distances.

I have only had my Prius since December, so does anyone know if the margin of error is different in Summer vs Winter?

 

Just returned to PA from a trip to Florida putting on 2850 miles. (7200 - 10050) Most of the miles were done around 68 - 70 MPH on interstate highways. Actual MPG was 49.3. Display showed 51.2 Red gen 3 II produced in June 2009. Great ride in the gen 3 except for the potholes on I-95!

 

Manufactured: January, 2010
371.9 mi driven added 9.024 gals. = 41.2 mpg calculated
computer estimate was 42.8 mpg giving a delta of +1.6 mpg more from the computer.

 

I have had my Prius since June.
I see the margin of error is very consistent (approx 6%) between stop/go city vs constant speed highway or summer vs winter.

Ken@Japan

 

When you get the computer version of mpg it is based on miles traveled via the odometer and gas used from the computer.

When you calculate from the tank fillup you use the odometer miles and the gas pump fuel refilled.

How could the odometer being incorrect or not allow you to determine an error?

3PriusMike

 

Good point!

My opinion is that the speed margin is not tied to the ODO reading, it is a requirement in many countries to enforce that the speed display is never less than the actual speed, so that the computer adds a margin.

In the same way, I'm guessing the engineers were asked to have the computer be more often optimistic on MPG rather than pessimistic.
Given the small MPG difference between the GenII and the GenIII (except maybe for highway), this had to be a marketing requirement.

 

I'm guessing that the speedometer is based solely on the rate of change of the odometer. And that the odometer reading and the fuel consumed goes into the mpg calculation. If there is any intentional error it would be in undercounting the fuel consumed, since the speed and odometer are probably legally required to be accurate within some limits.

Occams' Razor proves this.

3PriusMike

 

I've tracked it for 10 fill-ups (including a 3000-mile trip), and I'm seeing about 4-7% lower hand-calculated mpg compared to the display mpg. I'd say 5-6% is the most frequent offset. Typically this means about 4 mpg less than display says. My car was manufactured Oct. 2009.

 

According to my own calculation on every fill up for the past three months, the lowest consumption I got is 5.15 liter per 100km (Canadian metric system) occured on the last fill up. The Toyota Canada website is advertising it at 3.9L/100km. So my actual consumption is 32% more than what Toyota is claims. I don't expect to get that number anyways because of our cool weather up north. I'd be delighted to see it at around 4.5-4.8L/100km. In general, I am still satisfied with its fuel consumption.

 

On a related topic I have found out the following mpgs at these averages:

90 MPH = 35 MPG
80 MPH = 40 MPG
70 MPH = 45 MPG

does it roughly match your observations?

 

Based on 70MPH = 45 MPG and converts to KM/Liter consumption rate, it is 19.12km/liter.

My own calculation from the last fill up was at 19.43km/liter.
So it matches your report.
I think I am within the average range but driving the Prius always seems to be a self-chanllenge to reach the factory reported consumption rating. It's fun thought.

 

Wife just got her personal best mpg, 61.5 mpg with a/c going. This is computer mpg. Our calculated mpg varies by 1-3 mpg vs. the computer.

This little car never ceases to amaze me.

 

Already 21,000 miles on my 2010. Consistently computer says 51-52 mpg. Calculated amount close to 50 mpg.
cbo

 

[FONT=Courier, monospace] Decided while out of town yesterday to see what kind of fuel economy my three-week-old Prius III was capable of, with only 2000km on the clock.[/FONT]
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[FONT=Courier, monospace] I set “trip A” to “0” as I left the little university town of Wolfville, heading south on a secondary road through the agricultural heartland of Nova Scotia. My destination - the town of Annapolis Royal on the Bay of Fundy. I have driven this route a number of times in my Miata and been bored out of my skull because the road does not possess the necessary character to challenge an MX-5. [/FONT] [FONT=Courier, monospace]The route is a beautiful level drive though, through seemingly endless miles of bucolic fields and apple orchards filled with stunted, arthritic-limbed trees not yet in bloom. The posted speeds along the route vary from 50 to 90kph, although the regular appearance of tractor-towed manure spreaders, raw milk tankers, and slow moving military vehicles from a nearby base make attainment of those posted speeds highly unlikely. [/FONT]
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[FONT=Courier, monospace] I stopped at the only Toyota dealer on the route to ask their labor rate and was pleased to find it $20.00/hr less than my selling dealer in Halifax. Might actually be worthwhile driving down for service. While stowing a liter of Toyota's 0w20 I had purchased to carry in the car, I was approached by a seventies something farmer in a faded John Deer cap who wanted to ask me about my Prius. Would the Prius really give him better fuel economy than the old Pontiac Grand Am he was driving, he wanted to know. The salesperson had been giving him the worst load of BS about “thet lil Jap car.” After losing twenty minutes reassuring the old man that just about anything would give him better fuel economy than his present ride, I got underway again. [/FONT]
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[FONT=Courier, monospace] The only memorable highlight on the remainder of the trip occurred when I was nearly sideswiped by some moron in a SUV, who wandered across the yellow line to say hello. [/FONT]
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[FONT=Courier, monospace] Entering Annapolis Royal hours later, I noticed the car's computer indicated I had averaged only 43 kl/hr. But I had also managed to get an astonishing 3.1L/100km (approximately 91 miles per imperial gallon). Not sure what the mileage would be figured in US gallons, but I'd almost bet its better than what the old man could expect with his ancient Grand Am.

p.s. No calculated mileage yet. [/FONT]

 

Seaside Or to Portland Or airport and back. My wife and I left with 50 degree weather, rain, and wet roads. Went via highway 26, to 84 than 205.

Portland was cloudy with 64 degree. Picked up my mom and sister and their luggage.

We were loaded down and went back to Seaside Oregon. Total miles was 225.9, took 4.246 gallons. This trip started as sea level went up to over 1,600 feet on hwy 26 passes and of course back to sea level again.

Filled up at the same station in Seaside. Lowest price unbranded reg gas, with 10% Ethanol (all gas in Oregon has 10% Ethanol all year long).

Filled up the same way, first click than pull the hose. Computer indicated 53.8, calculated 53.2 MPG. I was impressed to say the least

25,000 miles on our Prius. 0X20 Valvoline synthetic oil, 4 quarts so not over filled. Michelin Energy Saver tires, filled up to 44 PSI, with Nitrogen in all four.

Alfon

 

This morning, after 450-odd miles of mixed driving. Dashboard: 51.7, Calculated: 50.6 mpg.

 

Motorway driving yesterday (236 miles) with the cruise control set to 70 m.p.h for most of the time but a little 50 m.p.h. driving through roadworks.

Indicated 64 m.p.g. (Imperial); calculated 62.2 m.p.g.

I must work out how to put my Fuelly link on here.