MPG Display Flabbergastingly Inaccurate

[Steverino]

Hello Tracer friends,

Why is the little MPG display thingie so inaccurate?

I track my mileage by calculating at the end of every tank.  Miles per tank, divided by gallons per tank, is a pretty precise measure of miles, per, gallon AFAIK.  By that metric, I'm averaging 44.1 MPG over 5 tanks so far, ranging over pretty consistent samples of 42 to 45.  However, the "Avg MPG" reading the bike is giving me is 47.0 MPG for the same period.  3 MPG IMHO is not a small deviation.

I've also tried cruising the highway in B mode, intentionally keeping speed way down (sub 60) to try and coax MPG out just as an experiment.  The instantaneous MPG shown is hilariously optimistic.  I read over 60 MPG (as high as 80+ on downhill sections, only as low as ~45 uphill) for the majority of a tank, with only a couple of red lights at endpoints to throw the average.  Yet that tank still only got me in the 44~45 MPG range.  In other words, almost a full tank of riding at a reported ~13 MPG over the calculated average still yielded - just the average again.

Now, this MPG doesn't upset me.  I'm riding an upper-mid displacement, sport-tuned bike, so 44 MPG is actually quite a happy thing.  But it does bother me that they set the dash up to woo you with "ECO" notifications and instantaneous MPG of 60 MPG+, when that's not what seems to be the case.  It's kind of miraculous that the engine can be so consistent with it's MPG over city and highway and spirited canyon riding, but why is the computer reporting so bad?

Note: I've never had another vehicle with instantaneous MPG reporting.  Is this just normal?  What is the point of showing instantaneous MPG if it is meaningless to your real world results at the end of a tank?

Addendum: I still love the bike, just disappointed in this one seemingly useful feature that has turned out to be pretty useless for me.

[BBB]

I have no idea whether you can set the units to be US gallons instead of UK gallons. Could be that it’s using the wrong ones?

As for the usefulness of that feature......I never use it myself, preferring to use the trip reset and aiming for a maximum 200 miles of range for a tank, but usually filling up when it makes sense well before that.

[Steverino]

43 minutes ago, BBB said:

As for the usefulness of that feature......I never use it myself, preferring to use the trip reset and aiming for a maximum 200 miles of range for a tank, but usually filling up when it makes sense well before that.

I've been trusting the fuel gauge.  So far so good, and it puts me at roughly 200mi per tank.  I'll experiment to see if there's a US/UK gallon setting.

[runnerhiker]

I have had numerous vehicles with instantaneous and average mpg calculations and displays, cars and motorcycles.  ALL of the average readings are optimistic, all of them, usually by 10%.  My 900 GT is also 10% optimistic, it reads 55 mpg and my calculations are 50 mpg.

That's the way it is.

[thejrod]

It's based on the duty cycles of the injectors. It's a fairly precise measurement, but over time some variance is introduced. My gallons-used gauge reads 3.8, and I end up putting in 4.0 (reading from the gas pump). So a bit over 5% optimistic. This affects the Avg MPG reading in the same way. 

So while there is a margin of error to be expected w/ the bike, there's also a margin of error to be expected from the gas pump itself. I'd bet my lunch money that most pumps are calibrated to read ever so slightly on the high side (in favor of the gas station, but within tolerance).

[runnerhiker]

57 minutes ago, thejrod said:

. I'd bet my lunch money that most pumps are calibrated to read ever so slightly on the high side (in favor of the gas station, but within tolerance).

I worked in the petrochemical industry for many years, product transfer across all boundaries of the industry are measured very precisely, all parties involved are interested in accuracy.  At the gas pump, the state's agencies are the last link in the chain and they protect the consumer by checking pumps.  It's not just a matter of catching bad actors, but bad actors are severely punished.

[Steverino]

If there is an industry-wide issue where all of these systems run 10% optimistic, why wouldn't it be corrected for?  What is the purpose of a system that is known to be 10% off all the time?  This is my question.  Are they trying to use it as a marketing thing to trick you to thinking you're getting better mileage than you are, as if no one would notice?

[Larz]

17 minutes ago, Steverino said:

If there is an industry-wide issue where all of these systems run 10% optimistic, why wouldn't it be corrected for?  What is the purpose of a system that is known to be 10% off all the time?  This is my question.  Are they trying to use it as a marketing thing to trick you to thinking you're getting better mileage than you are, as if no one would notice?

The Hubris of the Digital age is the culprit, IMO. Shite, Google can't even get Text auto-correct right- yet their full steam ahead with autonomous cars. Should't come as a surprise that computer driven mileage estimators aren't accurate or that the're seen as must include items by manufactures.   

[fjrpittsburgh]

The MPG registering on the display is optimistic and really not all that helpful anyway.  When you're low on fuel, you have to fill up regardless of what the display shows.  I'm really happy that my speedometer is so accurate.  That's something I use all the time and it's extremely valuable.

I do reset my "A" odometer every time I refuel.  It's nice to see how many miles I ride on a tank.  However, the odometer isn't entirely accurate either, but at least it's a constant to measure with.

[duhg]

This weekend I'm going to use my gps as an odometer (still not perfect) and see how that differs from the bike's odo.

[tktplz]

I'm just happy that if need be I can ride 200 miles with no worries. I have friends with Gen 1 and 2 VMaxes that are on fumes at 100 miles. Heck, I used to ride a Gen 1. Look at the new Suzuki GS1100. Has a 3.8-gallon tank. Who designed that? Used to looking at 100-120 miles and more gas so 200 miles is easy to me now. Now if you want to think of this bike in FUN per gallon. Now you are on the right track.

[fjrpittsburgh]

Be careful.  You won't ALWAYS see 200 miles on a tank.

[wanderer]

Mine is almost always (not literally always) 10% optimistic. And it is annoying, because it would be so easy to calibrate it out. I'd love a user configurable calibration factor.

[Luma46]

As I stated elsewhere, my bike's fuel consumption and fuel used are showing consistently ~10% less. At the same time, speed is showing 8% higher and odometer 2% higher.

[Coop]

On 5/24/2019 at 7:48 AM, Luma46 said:

As I stated elsewhere, my bike's fuel consumption and fuel used are showing consistently ~10% less. At the same time, speed is showing 8% higher and odometer 2% higher.

Strangely enough I burned 3.49 gallons today and used fuel said 3.5 gallons.  Some GT's are off and some are spot on.  I haven't a clue why.