Discrepancy in Average and Calculated MPG

Speeo and odo errors certainly can be opposite, in the case of our Fusion (yuck), the odo is so close to actual it's not worth the effort to factor it for FE calculations. The analog Speedo reads almost exactly 1 MPH SLOWER than the digital dash indicated speed.

 

Speedo discrepancy is not so much error as deliberate misrepresentation brought on by legislation and liability mitigation.

Also, it varies depending on the destination market. In the UK, for example, the error is typically 10% overstated between 20 and 80 mph. So if the speedo reads 77 mph, you're actually going 70 mph. This was the case with my UK Prius.

 

2.80/galon ahh no way man! you guys suck lol

 

Don't know where you get that idea from, may be true in the EU, but not here.

 

He probably got that idea from a website called PriusChat, where it has been posted many times to many threads over the span of my membership.

Three decades ago, I got the idea from a usenet group called rec.autos.*.

 

Welcome to life in the hills.

 

I'd picked up on this probably 25 years ago when I had longtime subscriptions to car and driver magazine, motor trend etc. I don't remember which one, but in one version of the roadtest they would show the displayed speed vs actual at varied speeds. It was always 1mph under actual speed.

 

I keep a spreadsheet, and find that the actual mileage calculated by dividing fuel into miles is about 6.5% LOWER than the MPG indicated on the screen. Here are some of my more recent readings:

 

hi just wanted to ad what I noticed this week

filled car to full (until bowser clicked off just once)

drove 200km exactly at highway speeds of 110kph very hilly terrain some hills were up to 10km long and moderate grade, my battery (reasonable condition not perfect but not dead either, excellent around the city) hovered around 1 bar for 50% of the trip, I wont use my prius on this route ever again I couldn't even keep up with the traffic on some hills, everyone flying past smiling at me small children sticking their finger up and poking tongue out, could almost hear their parents saying "look kids idiot in prius cant even get up the hill" anyway that's another story lol ....

MFD displaying 5.5L/100 avg for the 200km trip

stopped at same brand gas station as previous fill with same overhead line type fuel bowser, filled car to full again until bowser clicked off just once

total fuel for re-fill was 12.0L

that's a 1.0L discrepancy (if both gas pumps are calibrated and working similarly)

 

I make it 0.5 discrepancy?

There's no reason to drive exactly 200 kms to do a calculation, btw. You need two values: distance (any distance will work) since last fill up, and volume of gas pumped when you fill up. Put those two values into a ratio equation with 100, and the fourth value is your liters per 100 km.

As an example with your values:



You're basically saying 200 is to 12 as 100 is to what. And the drill for determining "what", using your values for example, is: 12 times 100 divided by 200.

You can do this with a spreadsheet to automate it, but by hand works fine too.

Also, I wouldn't be concerned with discrepancies introduce by pump variations, they're relatively minor, and are pretty much cancelled out by even just two fill ups. Every subsequent fill up makes for more accuracy.

 

Hi Mendel Leisk

I didn't, 200k is just what the trip ended up being that day.

Sorry I mean there was a 1L discrepancy for the full 200k trip, not 1L/100 .. so yes 0.5L per 100

as 100 is to 5.5 as reported by the MFD

11L vs 12L -for the full 200k trip

cheers

 

I suspected I was preaching to the converted. Thanks for letting me off easy.

 

Update: Got to take Prius on a mini trip yesterday, just shy of 100 miles and so I took the opportunity to check the ODOmeter accuracy. Now, I did notice a very slight difference EB v WB on I-20, so clearly even the State of Texas cannot get this EXACT

The odometer error with the currently installed ( Continental Control Contact Touring A/S 88t BSW ) tires is 1% HIGH > The odometer records 10.1 miles for each 10.00 driven.

Note: Those were already installed on the used car, we simply replaced the one bad, one worn with like tires.

 

I find that strange. When I go uphill (like in the Rockies of Colorado, or mountains in California), I pass everyone. Sure, the Prius is making a lot of noise, and my mileage drops, but I don't care. You must have some awfully steep hills, or else something else is wrong.

 

Multiple 10+ mile moderate to high grade mountain hills with 110km/h speed limit, battery has just enough time to recover around 4 bars then your at the bottom of another 10 mile mountain hill.. Prius runs out of energy in no time .. mfd shows battery at1 purple bar after 4 or 5 minutes then the prius has a job to hold 90km/h

I notice your car is a 2010 they have a bigger engine and they also squeeze more limits from the battery, gen3 may be more useful in tough conditions than my old 2008

 

The speed limit here is 65-75 mph (depending where you are), which is 104-120 km/h. But you are quite correct, the 2010 does have a bigger engine. When I heard that they were starting to put a larger engine in starting with the 2010, I waited.

 

the gen3 cars also push the limits of the hv battery a bit harder! something like 15-20% more available battery capacity than gen2

"I think" in Australia hybrid Camry would be a much better choice if you use highways a lot but Prius wins hands down for a city commuter ..

 

Just got an email about this thread in my weekly "tapatalk" feed.

Though my car is a gen 3, 2010 FWIW I've been tracking actual vs indicated mileage for 40,000 miles and the system is 4.2% more optimistic than the actual mileage. 51.17 indicated, 49.13 actual.

My fuelly mileage shows higher because I stopped posting to it a while ago. It's ridiculous enough that I bother to track mileage in a spreadsheet, I don't need to track it on a website also!

 

I started out with just a spreadsheet, then decided to join fuelly. I found by dropping my existing values into a new spreadsheet tailored to fuelly format, I was able to import it all into fuelly in one step. Food for thought if you want to bring your fuelly account up to date.

Now, I basically enter the info in my spreadsheet, then immediately over to fuelly, repeat. We're only filling up about once a month though, lol.

My dash vs calculated error is 7.5% btw. Might have something to do with our 17" tires. But I kind of doubt it. And I run 195/65R15 snow tires every winter.