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90 Miles Per (US) Gallon on the NC700X

670cc

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First, the history: Back in May, 2013, on a still fairly new NC700X, I happenened on the Blue Ridge Parkway after gassing up at Cherokee, North Carolina, USA. I was heading northeast as far as I could go in the daylight available. As I rode at a leisurely legal pace, I realized based on the odometer and fuel gauge, that the fuel economy seemed surprisingly good (2012 models do not display instant or average MPG). I continued in a hypermile style mode until I was just too nervous about running out of fuel, so I pulled off the Parkway and gassed up at 293 miles and achieving 94.5 miles per US gallon. Going forward I added farkles to the NC like a big windshield, hand guards, and other nonsense that would increase frontal area and degrade the aerodynamics, thus I never expected to see 90+ mpg again. Upper 80s has been easily attainable, but not the 90s.

Fast forward to today, well, yesterday actually. I again find myself in the same scenario as in 2013, riding the same NC on the BRP. Again, due to some occasional slow cars ahead of me and my general slow legal pace, I make the mental associations between odometer and fuel gauge and realize the fuel economy is looking good. So I went into a hypermile mode: light throttle, average 45 mph speed (which is the speed limit), highest gear possible for the load, very minimal braking and only two break stops (there are no stop signs or traffic lights along the entire BRP). Seeing the final flashing fuel gauge appear alone at around 250 miles, give or take 5, I mentally calculate that the bike will run out of fuel at around 310-320 miles on the tank. I figure I’ll consider it empty at 300 just to have a safety margin. There is no gasoline for sale on the Parkway, so the fuel-up involves exiting the Parkway to a town known to have a station. It worked out that I pulled into a station with 289.3 miles showing on the NC trip meter. I filled up fully, as usual, until no more fuel could be added or it would spill over the tank neck, and was able to fit 3.211 US gallons. This calculates to 90.0965 miles per US gallon. So there, I did it again!

One might suspect that this one 289 mile tank with 90.09 MPG is a big anomaly, but it is not. I attached my NC’s latest Fuelly summary showing multiple tanks of mileage in the 80s on either side of this one. I fully expect the current tank, yet to be logged in fuel up #304, is running well into the 80s.

In the interest of full disclosure, I can say that the rear tire is near end of life. It’s reduced circumference will cause the odometer to read potentially a higher number of miles than what was actually covered. However, the speed readout relationship between the bike’s speedometer and the Garmin GPS is still very close, a difference on the order of 1-1.5% at most, so I suspect the tire is not affecting readings much. I also noted that the odometer miles covered were very close to the GPS’s trip prediction. I’m going to say that at worst, the odometer error could be as much as 2%, but no more. I would need to measure the tire circumference and compare to new, or find some measured mile sections to check odometer accuracy somehow, but I have no way to do that right now.

See attached photos. Without having witnesses, the photos is the best I can do.

Lastly, the primary reason for the great mileage on all my last 10 or so tanks is I have been riding in situations that call for lower speed. In my experience, speed is the primary factor in determining fuel economy on the NC motorcycle.

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Klap

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Wouldn’t the smaller diameter of the rear tire mean you went MORE miles than indicated?
( more revolutions per mile?)
 

670cc

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Wouldn’t the smaller diameter of the rear tire mean you went MORE miles than indicated?
( more revolutions per mile?)
Smaller tire makes more revolutions per mile which makes the odometer log more miles than actual, which makes the fuel economy appear better than it actually is. But as I noted, I don’t believe in my case it could make an MPG error of more than 2%. We could also argue that we don’t know the accuracy of the fuel station’s pump, but those are things we can’t discover with certainty. That is why I included the Fuelly log showing that with recent fill ups at different times and stations and different pumps have also yielded MPG in the 80s, so the 90 MPG tank does not appear to be abnormal for reasons other than my riding style.
 

670cc

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As I was enjoying my motorcycle rides last week in the Appalachian mountains, and marveling at the excellent gas mileage, another thought came to mind. Many of us note better gas mileage on twisty roads, assuming mainly that it’s because we are generally riding lower speeds. Then I remembered one other thing, that the motorcycle tire has a smaller circumference at the edge of the tread than in the center. Thus, when leaned way over in a corner, the wheels needs to spin faster for a given vehicle speed. Put another way, when in a lean, the wheel does more revolutuons per mile than when riding straight up. The net effect of lean on gas mileage calculations is to give a false higher result, as the odometer is going to count more distance than was actually covered. I did not do any math to determine how significant this error might be, but the numbers should skew in favor of better mpg results. There are internet posts and articles on the lean angle circumference effect. Here is one picked at random: https://www.datamc.org/data-acquisi...e-rolling-radius-and-correcting-wheel-speeds/ As for my experience with high gas mileage on the Blue Ridge Parkway, I’d say the lean angle mileage impact would be very minimal, as the Parkway curves are gentle and much of the time in the more northern section, the road is fairly straight anyway

In summary, gas mileage calculated in the twisties based off the motorcycle odometer should theoretically be falsely higher the more you are doing extreme lean cornering.
 

itsmenc700

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Increased speed IS the cause of reduced mileage on ALL bikes!
Since you're only doing 45mph, your at the correct speed to get the most out of a gallon.
Anyone going 55mph will get less and anyone going faster will get less still.
Kind of how gas mileage works.
 

the Ferret

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I would say increased rpms would be the cause of lower gas mileage vs just speed. Four stroke theory says on every revolution one of those is intake. The faster the intake stroke speed the more gas it is sucking in.

45 mph in 6th gear will lead to better gas mileage than 45 mph in second gear due to lower rpms and less intake (gulps of gas) strokes per minute (given a flat road and same wind conditions etc)
 

670cc

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I would say increased rpms would be the cause of lower gas mileage vs just speed. Four stroke theory says on every revolution one of those is intake. The faster the intake stroke speed the more gas it is sucking in.

45 mph in 6th gear will lead to better gas mileage than 45 mph in second gear due to lower rpms and less intake (gulps of gas) strokes per minute (given a flat road and same wind conditions etc)
That is true for the most part, but if running a higher RPM in a lower gear at a given steady road speed, the throttle opening will be reduced. Yes, there are more intake strokes, but the intake air is more restricted by the throttle such that the cylinders are partially filled (more so than at lower RPM). In other words there are more gulps per second but the gulps are smaller. If you’re maintaining a constant speed, everything has to even out. What I think is the biggest factor in efficiency loss at higher RPM is the increased frictional and pumping losses in the engine.
 

670cc

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Increased speed IS the cause of reduced mileage on ALL bikes!
Since you're only doing 45mph, your at the correct speed to get the most out of a gallon.
Anyone going 55mph will get less and anyone going faster will get less still.
Kind of how gas mileage works.
Since you mentioned “ALL bikes”, then besides gas mileage, we also need to say watt hours per mile, too, on some certain bikes that don’t burn gasoline.
 

the Ferret

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well in the case of the NC DCT it's low rpm torquey motor and eagerness to get into 6th helps it achieve it's good gas mileage, even though it is a relatively heavy motorcycle

Of course lots of factors in achieving good gas mileage... road surface, and variation in levelness, weight of bike, weight of rider, gearing/rpms, aerodynamics, tire pressure, chain adjustment and lubrication, normal frictional losses in the motor/drive train etc etc
 

dduelin

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I would say increased rpms would be the cause of lower gas mileage vs just speed. Four stroke theory says on every revolution one of those is intake. The faster the intake stroke speed the more gas it is sucking in.

45 mph in 6th gear will lead to better gas mileage than 45 mph in second gear due to lower rpms and less intake (gulps of gas) strokes per minute (given a flat road and same wind conditions etc)
I agree in theory but it doesn't seem to matter how hard I'm twisting the go handle as long as I'm riding in twisty mountain roads and the speed is 20 to 50 mph I get mileage in 70s close to 80. I think it has more to do with aerodynamic drag which squares with a doubling of speed. Since the speed is slow the drag is low and makes up for constantly getting on and off the throttle.
 

the Ferret

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This is the internet... Simple is not possible. :cool:
Motorcyclists by their very nature it seems, like to make things complicated... oil changes, suspension adjustments, screens, seats, luggage, tire pressures, chain slack, which brake pads to use, ergonomics, even hand grips the list goes on and on ....
 

mzflorida

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Motorcyclists by their very nature it seems, like to make things complicated... oil changes, suspension adjustments, screens, seats, luggage, tire pressures, chain slack, which brake pads to use, ergonomics, even hand grips the list goes on and on ....

Guilty! Laughed when I read it!

Actually, the banter is part of what I enjoy.
 

Rabbit

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Motorcyclists by their very nature it seems, like to make things complicated... oil changes, suspension adjustments, screens, seats, luggage, tire pressures, chain slack, which brake pads to use, ergonomics, even hand grips the list goes on and on ....
Not just motorcycles. Anything that requires skill people tend to over complicate. Horses, car repair, farming, martial arts the list goes on.
 

the Ferret

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Not just motorcycles. Anything that requires skill people tend to over complicate. Horses, car repair, farming, martial arts the list goes on.
lol I'm never on those kind of forums, only motorcycle forums, but it makes sense. Guess we should say "people" just like to over complicate things.
 
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