Computer MPG

[samfrank]

On my '13 Norge the computer says my average MPG is about 43-44 but the actual is more like 34. What gives? I don't ride for fuel economy just wonder why such a wide discrepancy.
Sam

[biking sailor]

The 2013 Stelvio NTX I had did similar, except the values were exactly the difference from imperial gallons to US gallons, 1.2 to 1, when I figured the mileage manually.  I was pretty convinced the computer was programed for imperial gallons, but nobody ever confirmed my suspicions.  My other bikes, BMW, Triumph, Hondas, are pretty spot on.

[Kiwi_Roy]

That's interesting, fuel injectors work in the choked flow mode, the flow while the injector is open is fixed, not effected by manifold pressure, so if you know the length of injector pulses you can calculate the consumption quite accurately. Easy-peasy for the ECU

[idahorider]

My Breva is the opposite. If the computer says 37, reality is 42. Computer on my F150, though is a couple mpg optimistic. Not sure any are real accurate.
Paul Emerson

[jas67]

My Breva is about 10% optimistic.    If it reads 50 MPG, I'm getting 45.

[Lannis]

My Breva is about 10% optimistic.    If it reads 50 MPG, I'm getting 45.

My '09 Stelvio one is pretty accurate.   It correctly shows that I get about 15% higher mileage out of a tank of real gasoline rather than E10 .....

Lannis

[canuguzzi]

Are you reading the instant or the average? I thought mine was way off until I set it to read average. Also, if you swap modes for that reading then expect things to be off unless you're riding for some distance.

[Gliderjohn]

My 2011 Norge does similar. If I am showing 42-45mpg I am actually getting 36-38.
GliderJohn

[willowstreetguzziguy]

08 1200 Sport - Right on MPG

[Lannis]

08 1200 Sport - Right on MPG

Hmm; the '08 and '09 MPGs are right on target - the later model ones are optimistic.

I think that technology is starting to take control and get out of hand .... !

Lannis

[JeffOlson]

My 2014 Norge is off a bit, too.

[molly]

It looks like your computer is working in imperial gallons. There have been cases like this before.
I'm not sure if it can be changed even with a remap.
We have had a couple I know of in the UK working in US gallons.

[bratman2]

My 09 Norge is pretty close. It usually is with in 1 mpg.

[Kev m]

My Breva is about 10% optimistic.    If it reads 50 MPG, I'm getting 45.

When I used to check that bike, it was usually within 1 mpg.

Variables?

US (how we fill, where we fill, how we ride)...

[bpreynolds]

On my '13 Norge the computer says my average MPG is about 43-44 but the actual is more like 34. What gives? I don't ride for fuel economy just wonder why such a wide discrepancy.
Sam

Same with the 2011 Stelvio I used to own.  It was absolutely off every single fill up by roughly 4-6 mpg on the tank.  Coulda been that Imperial thing, never thought of that. 

[jas67]

When I used to check that bike, it was usually within 1 mpg.

Variables?

US (how we fill, where we fill, how we ride)...

I can see how that would affect the actual MPG, but not the accuracy of the measurement.

Now, one thought that comes to mind is that you owned it for it's first 15k miles, and I've had it for the following 11k miles.     The ECU measure the fuel usage by knowing the amount of time that the fuel injectors are pulsed on, their designed flow rate, and fuel pressure.    If the fuel pressure is higher than the ECU thinks it is, or the injectors flow more than originally designed, due, perhaps to wear of the orifices over time, then, more fuel gets used than the ECU thinks is being used.

[mtiberio]

my cal 14 computer was always worse than what I hand calculated (talking average/tankfuls).

The way the computer does it, they have to have a fudge factor in the computer telling them how much gas flows per microsecond of injector open time. The computer can count squirts, it can count solenoid open times, but it cannot know how much gas ultimately flowed. Here it has to make an educated guess.

In science, if you have a small number (like gas per squirt) multiplied by a large number (like number of squirts), any error in the small number will make the product of the two numbers inaccurate, sometimes wildly so. When a computer tells you MPG (whether it is instantaneous or average), it has to assume it knows how much gas it squirted, and how many miles you traveled. Since knowing how much gas is squirted doesn't make the bike run better or worse, poor accuracy on this number carries little penalty. The computer only needs to know if it needs to squirt more or less (to make the bike run right), the actual value is irrelevant.

[bad Chad]

My Breva is about 10% optimistic.    If it reads 50 MPG, I'm getting 45.

My Breva is about 10% pessimistic.   :-\

[rodekyll]

I thought this topic was going to argue the fuel economy of PC v mac.  I'm disappointed.   :bike

[Kev m]

I can see how that would affect the actual MPG, but not the accuracy of the measurement.

Now, one thought that comes to mind is that you owned it for it's first 15k miles, and I've had it for the following 11k miles.     The ECU measure the fuel usage by knowing the amount of time that the fuel injectors are pulsed on, their designed flow rate, and fuel pressure.    If the fuel pressure is higher than the ECU thinks it is, or the injectors flow more than originally designed, due, perhaps to wear of the orifices over time, then, more fuel gets used than the ECU thinks is being used.

Or you just suck at filling it to the same level... :-*

[bpreynolds]

my cal 14 computer was always worse than what I hand calculated (talking average/tankfuls).

The way the computer does it, they have to have a fudge factor in the computer telling them how much gas flows per microsecond of injector open time. The computer can count squirts, it can count solenoid open times, but it cannot know how much gas ultimately flowed. Here it has to make an educated guess.

In science, if you have a small number (like gas per squirt) multiplied by a large number (like number of squirts), any error in the small number will make the product of the two numbers inaccurate, sometimes wildly so. When a computer tells you MPG (whether it is instantaneous or average), it has to assume it knows how much gas it squirted, and how many miles you traveled. Since knowing how much gas is squirted doesn't make the bike run better or worse, poor accuracy on this number carries little penalty. The computer only needs to know if it needs to squirt more or less (to make the bike run right), the actual value is irrelevant.

Squirting Science.  Hmm.  I dunno.  I'm going to ask Fox News about this.  They love science. 

 ;D ;-T :BEER: Happy Thursday.

[jas67]

Or you just suck at filling it to the same level... :-*

If that was the case it would be high sometimes, and low others.   Over the long haul, it averages out to 10% optimistic.
 :P

[Waltr]

My MPG reading is pretty accurate if I factor in warm up from cold.  If I am checking the numbers I add 2 miles for every time the bike has to warm up in the summer and 5 miles in cold outside temps.   So if I am filling up the tank and I have been doing a lot of rides on that tank I add the starts up and factor that into miles ridden and always pretty spot on then.   

[Kev m]

If that was the case it would be high sometimes, and low others.   Over the long haul, it averages out to 10% optimistic.
 :P

No, you could just be THAT BAD...

[Spuddy]

My 2013 Stelvio is approximately 10% optimistic.

[Kiwi Dave]

We have had a couple I know of in the UK working in US gallons.

I believe they all work in US gallons, including two 1200 Sports and a 1100 Breva I purchased in Southern California.

It's easy to compare with the liters/100km figure.  My bikes typically would indicate an average of 5.5 liters/100km.  That equates to around 43 mpg US or 51 mpg UK.

Not that any of these figures were accurate, but I've had no reason to doubt them.