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  1. Default Gas Mileage East to West vs West to East or Summer vs Fall?

    Hi! Not sure where to ask this so I'm trying here, because I don't know if I'm dealing with a car that needs work, seasonal weather, route differences, or some cross-country headwind I don't know about. So, do people find that they get poorer mileage on east-to-west cross-country trips vs west-to-east, or fall/colder weather trips vs summer? I did and I'm very curious if this is unusual.

    I drove a 2009 Honda Fit stick shift, with around 24000 to 29000 miles from first to last cross-country mile, in both directions between Sacramento, CA and Madison, WI. Both times there were two passengers and the same amount of stuff in the trunk and back seat and the driver stuck faithfully to speed limits. The car was driven only a couple hundred miles in between the two long trips.

    Eastbound: Late May, lots of air conditioning. 80 to Salt Lake, then a detour to Moab via 191, then 70 to 76 back to 80 in western Nebraska -- same jag up through Iowa to Madison. Car killed it going through those mountain passes in western Colorado. Average mpg = 42.

    Westbound: Early November, just a little bit of heat for the evening hours. 151 to 30, then 80 all the way from Des Moines. Very few off-highway jags of no more than a few miles. Average mpg = 39.5, and that was only after coasting down the last stretch of 80 -- up until Salt Lake, it was down to 37.5 and only slowly crept back up until the Donner Pass. Car did not kill it at all.

    Any ideas from folks more familiar with road-tripping than myself (or suggestions of where to ask this if I'm in the wrong place)? I would've thought the air-con would make the summer trip worse, but maybe the engine really didn't like the cold? Or maybe the mountainous Colorado route made up for the air-con by allowing even more coasting than I could do through the milder passes in Wyoming? So puzzled. The only other thing I can think of is if maybe the speed limits on the southern Utah/Colorado detour were lower enough to make a difference over the average.

  2. #2
    Join Date
    May 2003
    Green County, Wisconsin


    Welcome to the RTA Forum!

    There are so many factors that go into gas mileage that it really is hard to say what your issue might be. Traveling west to east might give you slightly higher gas mileage on average, because you're a bit more likely to have the wind at your back. Traveling in summer will usually be a bit of an advantage too, as your car is usually going to run a bit rougher as it gets up to temperature in the winter, although extremes either way are a bad thing.

    But there are so many other things it could be. Speed is a huge factor, and if you were traveling on average just a few miles per hour slower, that could be a factor. If you made a couple more stops, or even had to idle a bit more, that can quickly drop your mpg numbers. If you saw some weather one way or the other, that could change your numbers. How you were shifting could be a factor, and even the actual gas you were filling your tank with can make a difference, especially if you had a few non-ethanol fill-ups in there. If your tires were a a little under-inflated, that could drag your mpg a bit.

    But honestly, the difference between 42 and 39.5 is less than 10%. In the scheme of things, that's just not that much. At least not enough where it is going to be easy for you to pinpoint a single issue. If you were typically getting 20 mpg, and you saw it drop by 4 mpg, then I'd say you might have a car issue that needs to be checked out. Based on the numbers you've seen, I'd say it's simply a case that every roadtrip is different, and that difference can include gas mileage.

  3. #3
    Join Date
    Mar 2005
    Tucson, AZ

    Default What You Can Control - And What You Can't

    First of all, I agree with Michael that the difference in gas mileage that you're reporting is essentially inconsequential. In addition, there are several variables in your report that would tend to increase mileage eastbound and decrease it westbound. As noted, there are the prevailing winds, but two items are even more influential. The fact that you were running your air-conditioning eastbound would tend to lower mileage in that direction, but the factor that you've ignored is probably even more influential and both increases mileage eastbound and decreases it westbound.

    While most people think of the Midwest and Plains as 'flat-as-a-pancake' that is only partially correct. They're flat in the sense that they have no obvious grades or hills, but they are significantly tilted, like a ramp, being at an elevation of roughly 6,000 feet near the FrontRange in Colorado and nearly sea-level where they hit the Mississippi. That's nearly 800 miles of constant downhill going eastbound and nearly 800 miles of constant (if slight) uphill while going westbound.

    Now, there's nothing you can do about the prevailing winds or the topography, and I'm not going to advocate turning off the air-conditioning in the summer since driving at speed with the windows rolled down is an even worse drain on mileage. Those are things you really have no control over. The one thing that you do have control over is how you use the gas pedal. The greatest 'trick' I ever learned was to treat the gas pedal as though it were a fresh egg. Do nothing that would crack that egg. Soft accelerations and almost no pressure while maintaining speed. Also: keep aware of what's going on well ahead of what you would normally consider; watch for slowing traffic well ahead of a few cars in front of you; be aware of 'stale greens', lights that have been green for too long and are likely to turn red before you get to them (best indication: light is green, but cross-walk signal is red). If there is slow or stopped traffic ahead, or a red light, why is your foot still on the gas?

    Another tip for Interstate driving is to travel at wave speed, in between clumps of traffic. The next time you're out driving on a rural Interstate, pay attention to the traffic coming towards you. What you will see is that traffic tends to travel in bunches with large empty spaces in between. The clumps tend to be about a mile apart and tend to travel at the same speed - wave speed. The individual cars will move in and out of the clumps, moving faster or slower than wave speed, and in having to speed up/slow down when caught by a clump, they waste gas. Your objective is to figure out wave speed, settle down into a space between clumps, and simply maintain that speed. The easiest way to determine wave speed is to settle on a speed and count the cars that pass you and that you pass. If more pass you, you are gong slower than wave speed and vice versa. Continuing adjusting your speed by small amounts until you determine where there are the fewest net passes, That's wave speed. Get in between a couple of clumps and adopt that speed.


  4. #4
    Join Date
    Oct 2008
    Joplin MO


    I always get better mileage from west to east than east to west. Without fail. Headwinds/tailwinds are a factor, as are A/C use, speeds, ethanol percentage, and winter/summer blend.

    I also get my BEST mileage at high altitudes, even burning 85 octane mountain gas. Octane is a nonissue in my vehicle, it will burn anything and it does NOT get better mileage on high octane fuel.

    It gets its WORST mileage on the low energy California gasoline, that stuff is just terrible - especially Arco and Costco. The only California gas that gives me halfway decent mileage is Valero.

  5. #5
    Join Date
    Nov 2005
    Ft. Collins, CO.


    Westbound often has significant (sometimes FEROCIOUS) headwinds. in my part of the world they close the interstates when semis start getting blown over.....

    Don't forget that tire pressure could be different between the two trips due to temperature. May is hot with air conditioning. November is cold. Even starting at the same "cold" tire pressure, the operating tire pressure could be more for the May trip.
    Or you might even have put new tires on the car and that alone can change mileage.

  6. #6

    Default Great stuff, and.................

    ......exercising some "skinny pedal discipline" as opposed to using cruise control always helps my mileage.

    I'm not suggesting never using cruise control, but when the terrain is even slightly rolling, if I'm aiming to maximize mileage, I turn off the cruise and get serious about the skinny pedal. The technique involves minimizing the changes in the amount of pedal you have depressed and minimizing how much you vary it. You essentially leave the pedal in the same position it's in on a flat stretch when you start downhill, let the vehicle increase speed somewhat, and let it bleed off a few mph on the uphill. If my truck increases 5 to 7 mph downhill and slows 5-7 mph uphill, and remains constant on the flats, that's about as efficient as it's going to get. For giggles, leave the cruise control set on a rolling terrain, and leave your foot gently in contact with it as you go up and down hills. You'll probably be surprised at how much pedal the cruise control applies to maintain speed uphill. Not only that, but it does "dumb" things like leaving your speed exactly as set until the base of the hill, then nailing the throttle to maintain it uphill rather then letting it speed up a tad downhill and carry the speed a bit uphill. This is of course an "under way" application of AZ Buck's "egg theory".

    To emphasize what's been noted earlier, I rather suspect the variances in mpg, which are statistically almost meaningless, are more due to wind resistance than any other single factor, and quite possibly more than all other factors combined. Even a mild headwind of 10 mph is aerodynamically identical to driving the vehicle 10 mph faster, and in a full-size pickup like my Ford, adding 10 mph drops my mileage by between 1 and 3 mpg, with the 1 being between 55 and 65 mph and the 3 being between 65 and 75 mph. If I want to lose 5 to 6 mpg from optimal, I can run 80 mph. We too often don't realize how much wind resistance changes with increased speed. It's not a linear variance, not at all.

    Lastly, what's said above about westbound headwinds squares completely with my own experiences and those of a friend. I was westbound across Nebraska and Wyoming on December 31/January 1 2010-11 and had 35 to 50 mph headwinds (and subzero cold). Truckers were complaining about fuel gelling and a number of them were stranded because of it. I'd treated my diesel heavily with that in mind, so my only problem was the wind. I can get over 20 mpg in my truck at 50-55 mph on flat ground and calm winds. I got 11-12 mpg over those two days. A friend drove the same stretch in a Jeep Cherokee during summertime and with a huge headwind. He pushed hard to keep his schedule, and the hard charging overheated his automatic transmission, stranding him in Cheyenne, WY at a transmission shop, from which he emerged a day later and $2,200 lighter in the wallet.


  7. Default

    So interesting -- I've found a number of things about warm/cold weather differences, but I'd started by looking for west/east differences and found nothing, so it's nice to hear that others have noticed this, too.

    I never *really* thought my car needed work because I do know it pretty well, but I wanted to cobble together what the various things might be because I'm a nerd about this stuff and suspected it was a combination but wasn't too sure. Hence my attention to what seems like an insignificant change -- sure, it only added up to about three extra gallons of fuel, but 42 has been my typical average for four years of local driving and shorter trips, so to have met that on one trip and not another was a surprise, especially because I do all the things folks are talking about (and because my local/shorter average stayed the same for the few months the car was in Wisconsin, it's first home outside of California). I drive at wave speed, I'm serious about the skinny pedal (even though I've never heard that particular term -- ha!), I inflate my tires a couple of ticks up to compensate for the cold, etc -- and I definitely idled less on the second trip than the first. Altogether I'm a very aware driver (this is how I get 42 to begin with), but I am one who up until this trip hadn't done a long east-to-west trip or done much cold driving (and dang was it *cold* in Nebraska!) with this car. Now I wish I could do the east-to-west trip again in the summer to see if I would come out in between or what -- because while a few gallons might be statistically insignificant, it's not insignificant as a curiosity.

    Anyway, thanks for all the thoughts! And, as a side note -- glc, I'm with you. I much prefer Valero to Arco. It's my go-to.
    Last edited by g_grrl; 11-14-2013 at 05:08 PM.

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