Gas milage

Discussion in 'Fiesta ST Chat and Discussion' started by WScottCross, Feb 4, 2014.

  1. Zormecteon

    Zormecteon Active Member

    I've seen if off by about 3 and half mpg or so.
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  3. F1ST

    F1ST Member

    I track my mileage on Every entry i log the trip computer mpg, mph, dte. You can get a good idea of how accurate it is from my logs. F1ST with the 1337 miles picture. Mine seems to be very close to actual with a few outliers.
  4. smatty

    smatty Member

    Isn't that like one or two percent? That seems accurate enough for my uses.
  5. Zormecteon

    Zormecteon Active Member

    more like 10% to 15% .. 30 divided by 3 = 10. Nearly every one of my tanks has been off by 10% or more... If i do all city driving, or all highway driving, it's pretty close, but I do a freeway run of a couple of hundred miles then finish off the tank in town, its WAY optimistic, and I've never had it report fuel economy worse than actual. It always reports better.

    If it makes you feel good, go ahead and believe what the car reports, but know in the back of your mind that it's not true. Don't believe me either. Do your own checks...... or not.
  6. smatty

    smatty Member

    Maybe my math is wrong but let's say I got 27mpg actual but the computer told me 30mpg. That's a difference of 3 so 3 of 27 is 11% and 3 of 30 is 10%. So isn't that a 1% difference? Am I way off on that?
  7. Zormecteon

    Zormecteon Active Member

    Your math is wrong. If it says you got 27 and you really got 30, that's either a 10% or 11% error depending upon if you take the reference point as 27 or 30. .. As in... .. If i have an original purchase price of $1.50, and take 1/3 off, (33%) it now costs $1.00, but if i start at $1.00 and raise my price by 50%, it now costs $1.50 .... .. but i don't subtract .33 from .50 and say that prices changed by 17%....
  8. kvetcha

    kvetcha Active Member

    I've got a lifetime average of about 26.9 mpg, mostly city. About 6000 miles on the car.
  9. smatty

    smatty Member

    Wow, I'm an idiot. Okay so it's off by like a whole gallon per tank? That's a lot. I'll have to double check the accuracy on my mpg estimater.
  10. Slowclimb

    Slowclimb Active Member

    It's good enough for me...I don't care about mpg enough to track it beyond what Ford tells me I'm getting.

    Sent from my SAMSUNG-SGH-I747 using Tapatalk
  11. MasterPooBaa

    MasterPooBaa Member

    And you fill the tank on the level up to the 'click' mark each time?
  12. MacDubois

    MacDubois New Member

    As long as I leave the Average mpg on the screen I drive more conscientiously and I get 33-35mpg.

    If I don't have it up I have much more fun and I'm down around 28.
  13. CarefreeAZ

    CarefreeAZ Active Member

    Fuel mileage (actual):

    2014 ST @ 10000 miles: 30.3 MPG with a 63/37 City/Highway split
    2011 SES @ 65000 miles: 35.7 MPG with a 56/44 City/Highway split
  14. Mayhem

    Mayhem Active Member

    My car reads very close. I keep track of it all on paper anyway and on fuelly ... but the car reading is quite accurate. That said.. 30 mpg is just not realistic for me.

    Sent from my SGH-I337M using Tapatalk
  15. spangenb

    spangenb Active Member

    I never really thought tires had a huge impact on mileage, but I ran the Cobb 91 tune for over a week with my snow tires on and still got around 30. As soon as I put the 225/45-16 Direzzas on I lost about 3 mpg. Now I can't break 27 in daily driving. We took a 2 hour highway trip and got just over 30. Could the tires really make that much difference? I suppose it's a combination of rolling resistance and wind resistance.
  16. MasterPooBaa

    MasterPooBaa Member

    It would mostly be rolling resistance. Apparently steel rims can also improve performance (less wind turbulence), and supposedly those low rolling resistance eco-tyres can give you a couple of extra MPG - at the expense of much grip :)
  17. Zormecteon

    Zormecteon Active Member

    One of the car magazines did a test within the past year of the difference made by using various wheel sizes. I can't remember the car, or the specific sizes used, I do remember the results. IIRC they started with 16s, and every time they went up a wheel size they went down a aspect ratio so that over all tire diameter stayed the same. At the same time they kept increasing the width, by 5 mm or 10 mm each time. They were testing for acceleration, cornering, braking, and fuel economy.

    The first step up was a minimal change. The next step they lost about 5% in fuel economy AND fuel economy. the next step was a 10% loss from stock on both, and about 10% again for the next size up.

    If you're looking for economy, put stock Fiesta wheels and tires on the car. It will also accelerate better, it just won't handle as well.
  18. spangenb

    spangenb Active Member

    Good info Zormecteon. I figured there would be some effect and the 10% is what I am seeing. No big deal. Since my car is a four season car I pay for my summer fun with my winter economy ;-)
  19. reddog99

    reddog99 Active Member

    You didn't specify what size your snow tires were, but the size difference between them & the Direzzas would change the odometer accuracy and this is what makes your mileage appear to change.

    If you were to account for the difference in the odometer accuracy between the two tires, you might find that your actual gas mileage hasn't changed at all. For example, if the Direzzas are a larger diameter than the snow tires, they would cause the odometer to register fewer miles and make it appear that the gas mileage is less.

    You can check your odometer by comparing it against the mile marker signs on any good long stretch of road, the longer, the better. If you can't find any signs on your county roads, then the interstates have the mile marker signs for certain. Convert this difference to a percentage to compare any two tires. Notice that I said odometer, not speedometer. The two instruments can have different error rates due to the way they operate.
  20. spangenb

    spangenb Active Member

    Good point reddog, but yes I accounted for that. In fact, I had a 4 hour interstate drive home when I bought the car so I took that opportunity to establish the factory odometer error which was less than 1%. The snows are 185/60-15 and the Direzzas are just 1% larger. I factor in the difference when I calculate mileage so the Direzzas really are near 10% worse mileage than the snows at least in my experience. Would be interesting to hear some other data points too.
    Last edited: Apr 28, 2014
  21. reddog99

    reddog99 Active Member

    Wow. I'm really astonished at that. I don't have any experience with them, but I would have expected that knobby looking snow tires would get worse gas mileage than the Direzzas, or anything else. Maybe the taller sidewalls give less rolling resistance? Glad to hear you've already accounted for the odo error.

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