On a trip out west this year, my gas mileage ranged from about 38-48 MPG. The higher MPG occurred when I was in the higher elevations. A friend said he had got up to 50 MPG going through CO one time. In the mountains, when I would get to one of the passing lanes, I could drop it down into 5th and gas it, when I would finally pass the vehicle I would be running like 75 MPH. Serious lack of power.

Can someone explain what was happening? I could understand maybe the reduced oxygen levels resulting in the reduced power. Any explanations from someone that knows?

 

I'd think thinner air would mean less MPG but I don't know squat about that stuff, so I'm subscribing to see if anyone can answer this.

 

My buddy had a 2010 Limited and would have the same problem when we would go through high altitudes, his wouldn't do more than about 55 going up hill. I had a 2007 and never had a problem with it. A lady riding the same bike stopped while we were fueling and she said she had the same problem going up hill. Harley told him to carry octane booster and put it in when he traveled through those altitudes. He got rid of it and now is a wing dingger.

 

While you will get significantly less MPG going up a hill/mountain that's nothing compared to getting infinite MPG on a fuel injected bike going down a hill/mountain. The combination of the two curiously will net out at an overall increase in fuel economy.

 

If you know your bhp here's a calculator you can use to figure it out

http://www.wallaceracing.com/braking-hp.php

 

I just learned that myself. Last year I rode through the mountains to get to Ohio the long way ( 220 North to 250 West right across the top of the Appalachians.) Lots of low gear climbing switchbacks, and many 9% downgrades,

I was surprised to find that I averaged 50 mpg on that part of the trip, significantly more than my 45 to 46 mpg average at other times.

 

Be ready for posters to call you all kinds of names. This has been argued on the forums for years.

The science museum in Pierre, SD, had an excellent exhibit a few years back. Two long, wooded troughs, both starting at the same height, both ending at the same spot "downhill." One trough was straight, the other was "down and up" all the way to the bottom, and was a visibly longer total distance due to the "hills." You put a marble in each trough.

Being a straight line is the shortest distance between two points, I was sure the marble in the straight trough would get to the bottom quicker. That was exactly opposite of what happened.

If you have a mpg computer in your car, you can easily see what happens to mpg and average mpg going down and up a river valley.

 

What year bikes are you guys running? Good grief! I've been through mountains *and* live in W TN where it's relatively flat and low elevation and I also am 260 pounds...my '09 FXD goes up hills/mountains with barely perceptible changes in amount of throttle twist in 6th gear. I know this as I ride to N Carolina via I-40 often. When off the interstate, I average 47 mpg. On the interstate I average 50 mpg and no matter where I am I can pass exactly the same as if I were back home on flat(ish) land on or off the interstate. This is on a *stock* '09, absolutely nothing done to modify *anything* on it. I'm thinking that the OP may have broke the engine in incorrectly and the rings aren't sealing as well as they could. Do a compression test on both cylinders and a leak-down test on both.

 

A bike with an injected motor shouldn't lose power at elevation. Mine never did when I lived in Colorado,and doesn't now,living in the mountains of eastern Washington. In the little hills they call "mountains" in the eastern half of the country,a carb could handle the slight elevation changes with ease. I average 45 mpg in the high country,with a stage ll 103 in the Road King. And have plenty of power at any altitude. In country like this..............



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Twistnride, you maybe didn't feel a loss in power, but it was there. Here's a HP/altitude calculator.

http://www.wallaceracing.com/braking-hp.php

100 hp at sea level is 85 hp at 5,000 feet, according to the calculator. Most dyno charts will specify the altitude the run was done at.


Here's another fun chart for those who like to race.

http://www.wallaceracing.com/altitudecorrection.htm