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I have had 2 fuel ups since I bought the bike and both of the avg MPG displayed were way off.

The 1st fill up, the computer showed 62.0 and it actually averaged out at 70 MPG with mostly highway miles riding back from Milwaukee to Illinois.

The 2nd fill up showed 54.5 MPG, but the actual was only 42.6. Mostly in town riding with my wife.

Has anyone else noticed this on their rides?
 

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I have had 2 fuel ups since I bought the bike and both of the avg MPG displayed were way off.

The 1st fill up, the computer showed 62.0 and it actually averaged out at 70 MPG with mostly highway miles riding back from Milwaukee to Illinois.

The 2nd fill up showed 54.5 MPG, but the actual was only 42.6. Mostly in town riding with my wife.

Has anyone else noticed this on their rides?
THERE IS NOTHING IN THIS WORLD THAT IS 100% ACCURATE -

(NEWSER) – Most clocks lose minutes over time and need to be reset—but if you're a scientist or an engineer, you need clocks that are just a bit more reliable. And now researchers at the National Institute of Standards and Technology have created the world's two most accurate atomic clocks. The next time they'll need to be reset—for a mere one-second delay—is in 50.8 billion years. The researchers' paper describes the significance of the development: It's like "specifying the age of the known universe to a precision of less than one second or Earth's diameter to less than the width of an atom."

The clocks, as all atomic clocks do, keep time using light frequencies and the fluctuation of atoms. But small movements of the atom or stray electric fields can interfere with the frequencies, so the new design—known as an optical lattice clock—minimizes these problems, holding the atoms in a vice-like grip, MIT Technology Review reports. And while you're probably thinking no one should be that obsessed with being on time, there are real-world applications. As Smithsonian explains, the clocks may help measure small changes in glacier ice thickness or tectonic plate movement; they're even useful for GPS systems.
 

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I have had 2 fuel ups since I bought the bike and both of the avg MPG displayed were way off.

The 1st fill up, the computer showed 62.0 and it actually averaged out at 70 MPG with mostly highway miles riding back from Milwaukee to Illinois.

The 2nd fill up showed 54.5 MPG, but the actual was only 42.6. Mostly in town riding with my wife.

Has anyone else noticed this on their rides?
You are correct, it is not worth looking at.
 

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Most all trip computer fuel consumption systems are quite inaccurate, more so on vehicles with smaller (fewer cylinders) engines. This, aside from the imperfect world issues highlighted by V8eyedoc, is for a number of reasons; a significant one being that most systems have no actual flow rate metering device, such as those used in filling station pumps. Instead the ECU calculates fuel consumption by combining what it knows of:

  • the fuel injector's flow capacity which is non-linear across its operating range and further affected by any given device's mechanical tolerances, electro-mechanical performance characteristics, and fuel pressure;
  • the operating fuel pressure (often just assumed to be the system design pressure);
  • the calculated injector pulse width;

The first two are the least accurate of the lot. And even though the pulse width calculated by the ECU is far more accurate it (when combined with the injector's actual capacity at the actual fuel pressure) makes the final fuel consumption calculation for any single injector at VERY best ±5% accurate for each calculation--more typically ±10%.

In a multi-cylinder engine the error tends to be "averaged out" and generally reduced, and reduced more the more cylinders. Nonetheless the error will remain rather gross making "MPG" displays more of a marketing gimmick than anything to bet money on.

There are aviation and other commercial fuel consumption systems that do use flow rate devices, though these most often report use in gallons or pounds per houir--much more critical information on a ship or in an airplane...
 

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My 08 400 has always been inaccurate and reads low by 3-5 MPG every time I check it. I have never found it to show a lower MPG that I actually got. With the small tank and high MPG, a small difference in filling the tank will show a large difference in MPG. You need to check the actual mileage over several tanks.
 

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If you do want an accurate MPG, you should always fill the same way and to the same level. I put mine up on the center stand and give the bike a little shake when the fuel nears the top of the tank. The filler port has a neck that extends down into the tank a little that will trap air and prevent you from really filling the tank. I usually shake and fill to completely top off the tank if I fill right before I'm going to use that extra fuel. If I'm just fueling and then putting the bike away, I'll leave some room in the tank for expansion of the fuel.

I've never filled while the bike was on the sidestand because it looks like the tank wouldn't hold as much while leaned over like that. I could be wrong though as the lean isn't all that much and I'm unaware of the actual shape of the fuel tank.

I don't recall ever having the MPG gauge on the cluster be "optimistic" and report a higher value than what I calculated though. Usually it's within about 2-4 MPG for me.
 

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The inaccurate speedo and odometer will contirbute an error factor for sure.
But filling the tank consistently is the biggest issue when doing manual calculations. The tanks on the 400 can get a rather large air bubble in them and look full but are not. Don't know about the 650's but I assume they have their particulars as well.
 

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The inaccurate speedo and odometer will contirbute an error factor for sure.
But filling the tank consistently is the biggest issue when doing manual calculations. The tanks on the 400 can get a rather large air bubble in them and look full but are not. Don't know about the 650's but I assume they have their particulars as well.
It's easier to get a consistent fill on the 650 because it has an extended filler neck with venting hoses that eliminate the air bubble you get on the 400. As long as you park on level ground and put the bike on the center stand you can get a fairly consistent fill up by bringing the level up to the cross bar visible in the filler neck. You don't have to do the rocking the bike to get rid of the air bubble routine like you do with the 400.

However the mpg meter on the 650 is no more accurate than the one on the 07+ 400. My 07 reads a little over 3 mpg low. The one on Robins 08 reads about 2 mpg low.
 

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I would be much more surprised to learn that:

A. The average or instantaneous MPG meter was accurate.
B. The speedometer was accurate.
C. The fuel tank level indicator was accurate.

It is an imperfect world if we focus on the detail. I fuel up at the 150/160 elapsed mile point, I record the fuel fill and calculate mpg later - but it 'is what it is' and is in essence a rear view mirror perspective of what 'happened'. Oh and I deduct 10% from my speedo mph reading to determine a more realistic speed OR if using GPS go speed limit + 10% except in town where I stick bang on the limit.
 

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Since the CPU on my 2006 won't display anything over 50.0 mpg, I record it all manually anyways. For winter and when MPG is less than 50.0 mpg, it's not too far off.



I have had 2 fuel ups since I bought the bike and both of the avg MPG displayed were way off.

The 1st fill up, the computer showed 62.0 and it actually averaged out at 70 MPG with mostly highway miles riding back from Milwaukee to Illinois.

The 2nd fill up showed 54.5 MPG, but the actual was only 42.6. Mostly in town riding with my wife.

Has anyone else noticed this on their rides?
 

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Around town the motorcycle shows anywhere from 39mpg to 42mpg. On fill-up, when I manually figure it (filling up to the crossbar in the nozzle) I get usually 58 to 59 mpg. Quite a difference. And this is multiple fill-ups so the single fill-up variation has been taken out of the picture here. I have already decided that the mpg the bike tells me is almost worthless. I will use the swag method (the scientific wild assed guess method) from now on to figure range when riding. That and the gas gauge (which isn't so accurate either by the way).
 

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i would be much more surprised to learn that:

A. The average or instantaneous mpg meter was accurate.
B. The speedometer was accurate.
C. The fuel tank level indicator was accurate.

It is an imperfect world if we focus on the detail. I fuel up at the 150/160 elapsed mile point, i record the fuel fill and calculate mpg later - but it 'is what it is' and is in essence a rear view mirror perspective of what 'happened'. Oh and i deduct 10% from my speedo mph reading to determine a more realistic speed or if using gps go speed limit + 10% except in town where i stick bang on the limit.
hahahahahahahahahahahahahaha.......normanb....you are 100% correct
 

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Being somewhat obsessed with fuel economy over the last 17 months that I've had the bike, I've checked frequently using the pencil and paper method to double check the computer figures. My 400z abs is pretty accurate on the computer comparing favourably with the pencil and paper brimming method figures. Rarely are they more than 1 to 2 mpg out by comparison. And when it was more than that it was (from memory) 2.5mpg difference. Still very close. Quite often I believe these differences are in the fuelling technique, not always burping the tank the same amount of times or whatever. It makes a difference. The ecu will take into account the injection pressure on each cycle and display the average result so it shouldn't be too bad reference accuracy. On cars here in 'Urop' the onboard computers are now very accurate on most cars. I suspect bikes still have a little way to go to match it but they are getting closer.
 

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Have you checked out www.fuelly.com as that is a fun site and you keep track of all your vehicles MPG, etc. you may like it.
 
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