2014 MPG Report
#21
09-30-2013, 07:50 PM
Elite HDF Member
Higher altitudes have less oxygen per volume of atmospheric available air. At about 10,000 feet above sea level for example, there's around 40% less oxygen per unit volume of "air" than at sea level. The O2 sensors sample of the exhaust gases will signal the ECM to instruct the fuel system to reduce the fuel in the mix, otherwise the bike would run too rich. So to keep the fuel/air ratio optimum, or within the range of the narrow band O2 sensors in late model HDs, fuel delivery has to be reduced when oxygen availability goes down. So the bike will use less fuel at altitude, but will definitely suffer a little regarding power. Maybe not noticeable to most at modest altitudes, but it does occur.
On the contrary, what happens to "most" carbed bikes at altitude? They continue with the same amount of fuel, with a lot less oxygen available, so they tend to run rich in the high altitude environment.
Another factor at altitude is cool dry air. For every 1000 feet in altitude, temperatures will decrease 3 to 5 degrees F. So during higher altitude riding, you have the advantage of cold dry air entering your air cleaner which enhances your fuel economy and, to some degree, offsets the power decrease caused by less fuel being delivered to the cylinders.
On the contrary, what happens to "most" carbed bikes at altitude? They continue with the same amount of fuel, with a lot less oxygen available, so they tend to run rich in the high altitude environment.
Another factor at altitude is cool dry air. For every 1000 feet in altitude, temperatures will decrease 3 to 5 degrees F. So during higher altitude riding, you have the advantage of cold dry air entering your air cleaner which enhances your fuel economy and, to some degree, offsets the power decrease caused by less fuel being delivered to the cylinders.
#23
09-30-2013, 09:59 PM
#24
09-30-2013, 10:14 PM
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#25
10-01-2013, 03:24 AM
Speedo accuracy
It's important to know exactly how many miles you have traveled between fill-ups. Until you verify the accuracy of your odometer, your mileage calculations can be incorrect, usually inflated. I think the new 14s may very well have good speedometers, within 1 mph of actual speed. That would mean that the odo would also yield a relatively accurate total miles driven. If so, all good.
But, if your speedometer reads 60 and you are only traveling 56 according to the gps you have mounted on the bike, then you have a 7.1% discrepancy in miles indicated versus actual gps miles traveled. So, on a tank your odo says you traveled 220 miles. Let's say you put 5 gallons in the bike at fillup. Based on this, you would think you are getting 44 mpg, when in reality you only traveled 204 miles with a real fuel economy of 40.8 mpg. So in this example there is a 3 mpg swing depending on the circumstances. YMMV
I know this may seem insignificant and maybe unimportant, but it's reality with most motorcycles.
But, if your speedometer reads 60 and you are only traveling 56 according to the gps you have mounted on the bike, then you have a 7.1% discrepancy in miles indicated versus actual gps miles traveled. So, on a tank your odo says you traveled 220 miles. Let's say you put 5 gallons in the bike at fillup. Based on this, you would think you are getting 44 mpg, when in reality you only traveled 204 miles with a real fuel economy of 40.8 mpg. So in this example there is a 3 mpg swing depending on the circumstances. YMMV
I know this may seem insignificant and maybe unimportant, but it's reality with most motorcycles.
Thats very easy to check. My OL was acting as my copilot keeping an eye on GPS and giving me directions, so when she says – follow this road for 30 km then turn right, I notice the odometer reading and then find the actual turn within 0.5 to 1 km of where the navi thinks it is.
It was different when I was having a wrong size tire – the discrepancy could be up to 10 percent high!
#26
10-01-2013, 06:07 AM
#27
10-01-2013, 07:48 AM
I find the speedo variance interesting. I have checked mine against a GPS and those roadside "Your Speed Is" radar units. My speedo seems to be on the mark.
The size of our tanks allows for some variance too. If you don't fully refill on a consistent basis then there will be discrepancies in MPG too.
The size of our tanks allows for some variance too. If you don't fully refill on a consistent basis then there will be discrepancies in MPG too.
#29
10-01-2013, 10:40 AM
What an utter nonsense. According to your theory in vacuum we could ride with zero fuel consumption. 
Alright, serious now. The energy contained in fuel is what makes your scoot move. Air pressure is irrelevant with EFI because it compensates for that (you get lean mixture with carburetor, not good for engine nor fuel economy), you still have to open throttle a little more to allow engine to output power needed for given speed. The only thing different in high altitude is the top end power, which is going to be less because to get power you need to burn fuel, which in return needs air. Less air > less fuel you can burn > less top power. That's why overcharging was invented - to pump more air into engine so it can burn more fuel and output more power.
Knowing a few terms about EFI is not enough if you want to make sense and stop people laughing. High school level physics knowledge is essential.
Alright, serious now. The energy contained in fuel is what makes your scoot move. Air pressure is irrelevant with EFI because it compensates for that (you get lean mixture with carburetor, not good for engine nor fuel economy), you still have to open throttle a little more to allow engine to output power needed for given speed. The only thing different in high altitude is the top end power, which is going to be less because to get power you need to burn fuel, which in return needs air. Less air > less fuel you can burn > less top power. That's why overcharging was invented - to pump more air into engine so it can burn more fuel and output more power. Knowing a few terms about EFI is not enough if you want to make sense and stop people laughing. High school level physics knowledge is essential.
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