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How to compute mileage (mpg)?



 
 
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  #21  
Old June 26th 05, 05:30 AM
DTJ
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On Sat, 25 Jun 2005 19:48:14 GMT, "No Spam" > wrote:

>"Newbie" > wrote in message
...
>> It may seem like a superfluous question, but what is the best way of
>> calculating what mmg yuor vehicle is getting? I have my miles reading
>> of course, and I can record how much gas I put in, but there was some
>> gas already there in the tank, and how do I know what was traveled on
>> how much gas? If you have a good system, please share!

>
>Amazing. Our educational system on display.


I was amazed the other day when I had a chance to work with a brother
(16) and sister (14) at a concession stand. They both would have
worked circles around almost every adult that works there.

Oh, the reason - parents own a store.
Ads
  #22  
Old June 26th 05, 04:12 PM
Don Stauffer
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Newbie wrote:
> It may seem like a superfluous question, but what is the best way of
> calculating what mmg yuor vehicle is getting? I have my miles reading
> of course, and I can record how much gas I put in, but there was some
> gas already there in the tank, and how do I know what was traveled on
> how much gas? If you have a good system, please share!


You need to mark the milage at each fillup. Then take the gallons at
each fillup. Take the milage since the last fillup (subtract previous
fillup milage from current milage. Take gas you put in this fillup.
This is the gas you put in, even if there already was gas in tank, and
the milage you drove since then, so it doesn't matter how much was
previously in tank.

Then; miles PER gallon. PER means divide. So divide miles by gallons.

Now, there are two trains of thought on how to handle statistics and
accuracy.

One thought is to take milage at beginning of several fillups. Now keep
track of gas used in ten fillups, milage at last fillup. Divide
cumulative milage by total of gas used. This MAY eliminate some small
measurement errors. But, it yields no statistics by which you can
measure accuray.

I prefer calculating milage each time, for ten times. Average the ten
readings. Now, compute variance. This is done by taking each
individual milage calculation and subtracting average. Square the
difference. Some all the squares. Now take square root of that sum.
Sounds like a lot of work, but with calculators it is a two or three
minute job.

Now, the average you compute is only accurate to within this square
root, with is the basic precision of your set of measurements. For
instance, I tried ten tankfuls of regular, ten tankfulls of premium, to
see which gave better accuracy. The value for regular was slightly
bette than the average for premium, but the amount of the difference was
only about half of the variance (that square root). Thus I could not
conclude that regular actually gave me better milage- I have to conclude
that they are the same within the accuracy I can measure my gas milage.
  #23  
Old June 26th 05, 04:26 PM
Mark
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You're so harsh... LOL

  #24  
Old June 26th 05, 04:28 PM
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In alt.autos.toyota Ad absurdum per aspera > wrote:
> To the good advice given elsewhere in the thread, I would add, "check
> your speedometer" (and thus your odometer). These things have some
> intrinsic error, which might either stack up atop or the other
> potential source of error: hanges you have made by tire/wheel size.


While not an issue with my Toyota, I've had several vehicles where the
odometer error is significantly less than the speedometer error.
  #26  
Old June 27th 05, 06:27 PM
Jeff Strickland
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The very best way is to ALWAYS fill the tank everytime you get gas, then
divide the distance you went, 250 miles, by the new load of fuel, 12.5
gallons. The result, 20, is your miles per gallon. Fill the tank and reset
the odometer (trip meter).

I consistantly get just a bit over 25 mpg, so in 300+ miles I put in 12
gallons of gas, for just over 325 miles, I put in 13 gallons, for 275 miles,
I get 11 gallons.

It doesn't matter how much gas is left when you fill up. It does matter if
you fill to the brim, or only fill to the first shut-off. I usually fill to
the first shut-off, then top off to the next even dollar. I used to top off
to the next even quarter, but gas is getting so expensive that topping to
the next dollar is less than a half gallon, and this won't change your
formula very much.

So, you go to the corner today and buy gas. If you filled the tank to the
top AND reset the odometer the last time you got gas, then you can divide
the distance by the new load of fuel and derive the mileage. If you did not
fill to the top and/or reset the odometer, then this tank will be your
baseline and you can make no calculations from it. Then, in a week or so
when you visit the filling station again, then you fill the tank and divide
the distance by the fuel load. The result will be your mileage. If you go
250 miles and put in 10 gallons, then you got 25 mpg. All you have to do is
always fill the tank, never just get $5.00, or whatever. If you do just get
$5.00, then you have to add the gallons to the next fill up and leave the
odometer counting as if you had not gotten the few gallons.

After you do this a few times, you will be able to quickly calculate in your
head to confirm that you are getting the same mileage that you always get. I
get 25 mpg in my normal driving routine.




"Newbie" > wrote in message
...
> It may seem like a superfluous question, but what is the best way of
> calculating what mmg yuor vehicle is getting? I have my miles reading
> of course, and I can record how much gas I put in, but there was some
> gas already there in the tank, and how do I know what was traveled on
> how much gas? If you have a good system, please share!



  #27  
Old June 27th 05, 06:32 PM
Jeff Strickland
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"Kathy and Erich Coiner" > wrote in message
news:byhve.1095$4M1.107@trnddc07...
> 1. Fill Tank.

Correct.

> 2. Record mileage.

Correct.

> 3. Drive car till near empty.

Sorta. Drive as long as you want and refill the tank anytime you want.

> 4. Fill tank again. Use same pump at same station. Let the auto shutoff
> system work. (Do this on initial fillup too. Record gallons to fill

You make this much more difficult than it needs to be. All that is needed is
to fill the tank where ever it is convenient to get gas.

> 5. Record mileage.

Correct.

> 6 mpg= (mileage step 5-mileage step 2)/gallons used step 4.

Correct. Repeat from Step 3.




  #28  
Old June 27th 05, 07:35 PM
ray
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Newbie wrote:
> It may seem like a superfluous question, but what is the best way of
> calculating what mmg yuor vehicle is getting? I have my miles reading
> of course, and I can record how much gas I put in, but there was some
> gas already there in the tank, and how do I know what was traveled on
> how much gas? If you have a good system, please share!


Start with a full tank.
record mileage.
Drive.
At next fill, record mileage and the gallons to fill back up.

With my truck I just go to the first click. Your mileage will vary
depending on the type of driving, the weather (-40 idling uses a lot of
gas) etc etc... so just keep tracking it.

I use a spreadsheet and track the average and the average for the last
10 tanks. I found the last 10 tankfuls to be a good indicator of my
overall mileage. I moved to a more rural area so I spent less time in
rush hour so the average mpg went up by a couple, but went back down in
the winter... and went up a couple mpg when I finally changed the plugs
and did a tune up.

My truck usually averages around 12-16mpg with the odd highway drive
above 20.

Why the average? Because unless you drive the same road under the same
conditions at the same speed with the same brand of gas filled to the
same spot in the tank you're introducing all kinds of "error" into the
equation. Averaging that over 10 tanks will give you a more "real
world" mileage.

If you have excel I can email you a copy of the spreadsheet...
Ray
  #29  
Old June 27th 05, 08:21 PM
John David Galt
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Newbie wrote:
> It may seem like a superfluous question, but what is the best way of
> calculating what mmg yuor vehicle is getting? I have my miles reading
> of course, and I can record how much gas I put in, but there was some
> gas already there in the tank, and how do I know what was traveled on
> how much gas? If you have a good system, please share!


One normally assumes that the tank becomes equally full right after each
fill-up. Therefore, all you need to do is reset your trip-odometer after
each fill-up, but first, divide the number on it by the number on the
pump. (In other words, the amount of gas you just put in equals the
amount you used between the previous fill-up and this fill-up.)
  #30  
Old June 28th 05, 02:44 AM
The Real Bev
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Newbie wrote:
>
> It may seem like a superfluous question, but what is the best way of
> calculating what mmg yuor vehicle is getting? I have my miles reading
> of course, and I can record how much gas I put in, but there was some
> gas already there in the tank, and how do I know what was traveled on
> how much gas? If you have a good system, please share!


Ask your little sister, she'll help you.

--
Cheers, Bev
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"He who joyfully marches in rank and file has already
earned my contempt. He has been given a large brain by
mistake, since for him the spinal cord would suffice."
-- -Albert Einstein
 




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