Why do we get better gas mileage in the Rockies?

[Ken R]

Took a 3,000 mile trip in the past 7 days.  Dallas to Trinidad, to Denver, to Moab, Utah, to Mexican Hat, Utah, to 4 corners, to Durango/Silverton/Ouray/Montrose, Aspen, Independence Pass, Buena Vista, back to Trinidad, and back to Dallas.   Great trip, highly recommended.

But the big question is:  Why did we get 10mpg better mileage in Colorado than in Texas?  REALLY!  10+ MPG better!

First tank netted 30.+ mpg from Dallas to wherever in Texas.  (strong crosswinds the whole way may have reduced mileage)
Next two tanks in Texas netted 34 mpg and 36 mpg.  Filled up in Clayton, New Mexico.
Clayton's tank produced about 39 mpg.
Next tank from Denver, across I-70 also produced 39 mpg. 
Next tank from Glenwood Springs to almost Mexican Hat resulted in 41 mpg.
Next tank from Mexican Hat to Ouray, Colorado resulted in 42.+ mpg.   
The route through Aspen and over Independence pass to Buena Vista also resulted in 42+ mpg. 
Buena Vista to Walsenburg, almost 43 mpg. (mostly 75 mph with cross or headwinds).  170 miles
Next fill up was back in Clayton, new Mexico . .. . 39 mpg
Amarillo:  34 mpg
Another 135 miles and filled up:  33 mpg
Another 140 miles and filled up:  30.49 mpg (running on fumes when we pulled into the station, only .4 gallons left). 

My traveling companion on an 05 Ultra stroker got 4 to 5 mpg better than me in Texas (both going and coming).  I got slightly better mileage in Colorado than he did.

Common sense would indicate that we'd get worse mileage in Colorado, where the air is thinner, a lot of throttle twisting, climbing, etc.   But that simply wasn't the case.  We all experienced the phenomenon. 

[hotroadking]

Well it's downhill half the time in the mountains
you riding slower in the mountains due to the curves and dangers
Temps Cooler up top
Less Headwinds and 100+ days in Tejas
More Ethanol in Tejas
Higher speeds and headwinds in the flats of Tejas

[MaxxV4]

That seems to be the case with all vehicles, fuel injected especially. I always get better mileage at altitude even though it seems like I am into the throttle more to compensate for the loss in power. I think it has to do with the drop in air pressure vs. closer to sea level where it is 14.7 psi. The fuel injection reads that and reduces the fuel needed. (I think?) Also, there may be more ethanol used in Texas than in Colorado and ethonal definately causes more fuel consumption.

[Dennis The Menace]

Cuz Texas and Utah suck (gas)  lol

menace

[Ken R]

Well, it was gosh-awful windy between Buena Vista and Walsenburg, out of the Soutwest.  On I-25, there are wind warnings.  It wasn't a relaxing part of the trip.
Speed limit on I-25 is 75 mph.  We generally rode at 78 to 80 mph.  But we got the best gas mileage on that tank fill-up.  (this was on the way home after splitting from the other three riders)

The people we rode with in Colorado had me at W.O.T. a lot.  I mean a whole lot.  I never do that in Texas. 

Oil temperature WAS about 10 degrees cooler.  Never got over 220 or so when in the 100+ temps of North Texas yesterday.

Also noticed that the Octane rating was lower in Colorado.  A rating of 89 was common.  The motor didn't complain. 

There's really something going on to cause this.  Maybe they don't put Ethanol in the gas for Colorado and Utah.  I don't know . . . .but would certainly like to.

Well it's downhill half the time in the mountains
you riding slower in the mountains due to the curves and dangers
Temps Cooler up top
Less Headwinds and 100+ days in Tejas
More Ethanol in Tejas
Higher speeds and headwinds in the flats of Tejas

[HarleyCharley]

We had a similar experience on a mountain ride through NC, TN, and Va last weekend. My bike, an '02 95" with 26g cams, a '01 88" with 510g cams, and an '02 107", all ultras got 48 MPG or better! Usually when my clock gets about 140 miles, I better find gas pretty soon. But I refueled with 160 miles showing and all it would hold was 3.3 gallons. I still find it hard to believe but there was two other guys with about 8 to 10 MPG better mileage. I think it has to do with the MAP sensor. 

I'm going to try it again, perhaps this weekend.

charley

[machinist]

I get better mileage with the lower octane fuels. I run Shell 89 in the dyna now, no ping.

[wolf_59]

Less air = less fuel
I routinly get 48 mpg here in the 4 corners, last time I rode the loop from Aztec - Durango -Silverton - Telluride - Mancos back to Aztec, I got 56 mpg
Sucks for trying to make power but fuel milage ain't bad
Can't think of any place I would rather live though

[bouncingVman]

Less air = less fuel

I think this hits the nail on the head. I always wondered the same thing, but came to conclusion that the air is lighter and therefore the EFI compensates with less fuel. Don't ask me... its just a working theory of mine.

[PoorUB]

I have run from Red Lodeg, MT to Cody, WY over Beartooth and then Chief Joseph and get 60 MPG with my '05 Ultra. I have run the route 3-4 times with the same results. I think it has to do with flower sniffing on the way up, and coasting all the way down.

[DblackmanC]

I think the miles up high are just shorter...LOL

[smoserx1]

Wolf_59 has the answer.  Less air = less power = better mileage = lower octane requirement. 

[Ajayrk]

And higher altitude means less compression so lower octane is ok.  Lower octane has a faster traveling flame front.  Octane additives slow down the flame front.

I was out that way last June and got 51 to 52 mpg.  Yep I was pleasantly  surprised.

[apehair]

Wolf_59 had the right idea, but on fuel-injected bikes it's about oxygen, not air pressure.  Particularly if your bike has 02 sensors.  They'll work to keep the oxygen-fuel ratio constant.  So, if you have less oxygen in the air, the fuel injection will deliver less fuel.  Better gas mileage, but less power.

I'm not sure if it works the same way on carbed bikes.  On carbed bikes it's about the volume of air that atomizes the fuel.  Thinner air would have an effect similar to a smaller throttle body opening, since less air would be available to atomize the fuel. But there would still be just as much fuel delivered by the jets.  Would the result be better gas mileage, a richer mix, or fuel piling up somewhere along the intake, unused.  I dunno.

I really enjoyed the theory that at altitude a mile is shorter.  LMAO.

ape

[FLTRI]

I routinely get in the mid-to-high 30s climbing up mountains and over 60mpg going down mountains, averaging in the mid 40s for the trip.

[Ken R]

I'd really like to know.  We saw over 10 mpg difference on two bikes measuring between Texas and Colorado/Utah, comparing apples to apples.  We ran highway speeds  on the first and last two tanks. Actually went faster on I-25 than US 287 in Texas.  

10 MPG, guys!  That's 50 miles more per tank!


Maybe the question should be rephrased:

Why do we get such lousy gas mileage in Texas?

[MaxxV4]

The good thing is that you have the same results from two bikes under the same conditions. It's no fluke. Now try riding across I-90 in South Dakota with their ethanol and prairie winds and be lucky to get 30 mpg......

[Jeffd]

maybe you got a generous gas pump on your best tank.

[IBARider]

I dunno.  I always figured it was due to going slower.  I certainly don't get better mileage on freeways at higher altitudes.  In fact, the worse mileage I ever got was between Missoula and Butte.  25mpg cuz I had that puppy wide open, 100+ ...

I disagree with less air, less fuel.  i do know that yes, an ecm delivers fuel according to air/oxygen, but that is less power so you open your throttle more so that kinda off sets that.  With all factors the same, it will take x amount of energy (fuel) to move x mass, x distance...

Those roads where you got better mileage... I've been on em and I know I go slower on em than I would in Texas.  I live in the sesert and I get 33 mpg constant.....and I can say it is directly related to my right wrist

[05FLHTC]

Just a guess here, I would be more inclined to believe the gasoline blending requirements in the individual States and areas have the larger effect on the MPG. Different area require oxygenated fuels for emissions, not good for MPG, it's been a while since I blended fuel for one of the major Refineries but different areas in the nation have different requirement & restrictions. One example is more butane into the mix will kill the MPG...this normally is blended at a higher volume in the winter months as the Reed Vapor pressure limit is raised during the winter months in the mid west. California gas blends had their own set of regulations...

[Jeffd]

I dunno.  I always figured it was due to going slower.  I certainly don't get better mileage on freeways at higher altitudes.  In fact, the worse mileage I ever got was between Missoula and Butte.  25mpg cuz I had that puppy wide open, 100+ ...

I disagree with less air, less fuel.  i do know that yes, an ecm delivers fuel according to air/oxygen, but that is less power so you open your throttle more so that kinda off sets that.  With all factors the same, it will take x amount of energy (fuel) to move x mass, x distance...

Those roads where you got better mileage... I've been on em and I know I go slower on em than I would in Texas.  I live in the sesert and I get 33 mpg constant.....and I can say it is directly related to my right wrist

I always get poor mpg between Missoula and Butte as well.  It is up hill all the way LOL.  Get better tho from Butte to Msla.