Avarage L/100 km wrong in my case. Why?

[Tutelarix]

I think the avarage L/100 km statistic is wrong. Check my page. I have the max L/100 km is 8.2; How the avarage can be 8.4?? Look detailed in more inside.

So,
Let's calculate avarage gas mileage for my car.

(7.3+7.6+8.2+7.1+7.3)/5=7.5 This is avarage mileage.

Let's calculate using the odometer km and liters.
I know that full gasoline tank is 55 liters. So, last time I fueled up on 46 liters, so there was 9 liters in tank.

So, I need to sum all my liters, take away 9 liters. I will get the liters of gas that I used for the last fuel up. And divide this number on last odometer number.

So:
30+42+45+51+25+41-9 = 225 liters.
The litters I used for 2985 km.
225/2985 = 0.07538
0.07538 * 100 = 7.54 L/100 km

This result is the same to my calculations with avatage milega, but in is not similiar with your results.

Please, check your calculation alghoritm, or write pls, where I wrong.

My e-mail is in profile http://www.fuelly.com/driver/tutelarix.

Thank you.

[pb]

To calculate your overall average L/100km we use total distance driven and the total fuel volume. In your case you've driven 2978.09 km and fueled 249.99 litres. If you use those numbers you get 8.4 L/100km. I'm not sure why we have different numbers. Keep in mind that we can't use the distance or fuel volume from your first fuel-up when you use odometer tracking. That might be the difference.

I also notice that your first fuel-up is a partial. When you mark a fuel-up as partial, Fuelly won't calculate an individual L/100km for that fuel-up or the next. But we do use those fuel-ups for your overall average. That's why you can have a situation sometimes where the overall average is higher than any individual calculated average. Once you have more than a dozen full fuel-ups or so this generally doesn't happen.

[Tutelarix]

>>>To calculate your overall average L/100km we use total distance driven and the total fuel volume. In your case you've driven 2978.09 km and fueled 249.99 litres.

Here is wrong idea of calculation.

I have driven 2978,09 km, but I not used all fuel. I just fuel up, so I have full tank. And so, for this distance I have used the 249,99 km - the liters of tank. (if last fuel up was full tank). (I not used the fuel that I just fuel up, because I havn't use it for driving. Here is the idea.)

You cannot take the values for odometer and all liters of fuel, you should take only the litters that was used for this kms. Odometer value and all fuel - the fuel in the tank.

The partial fuel-up don't have influnce on avarage L/100km. Because any way you use the last odometer and all liters.

Thank you for your responce.

[pb]

I see what you're saying. It might make more sense to use the fuel volume from the first fuel-up and disregard the fuel volume from the most recent fuel-up when we calculate the overall average. We're discussing it.

[DTMAce]

This is why I strongly dislike L/100K Its annoying. LOL

MPG or LPK are so much simpler and make more sense. Whoever came up with that method of determining mileage should have been shot.

I think he is over complicating it. Lets come at it from this direction:

You buy a car with X number of miles on it.

The first time you put gas in it (lets assume its a full tank fill up), you create your entry here and record the fill up. So you START with a full tank.

According to fuelly you have gone 0 miles and have used x number of gallons/liters of fuel at x cost already.

Fuelly of course will not give you a mileage yet, as you have not recorded a full tank to full tank usage.

Once you have your second fill up (assuming again its a full tank) you will get your first idea of your mileage. But according to the averages, you will have bought gas twice, yet drove the distance for one.

My suggestion there PB is this. Only drop the first fill up volume/cost recorded from the averaging of both volume and cost. This sets the BASE value (A baseline if you will) for your vehicle. But you can't use it for the calculating math. If you eliminate the first fill-up of values, you eliminate the discrepancy for the averages.

But I will point out, after hundreds of fill ups, the current method is not going to make nearly as much impact as it does with a few the way it is now.

He is saying that, because we are counting all the fuel, dividing that into the total distance driven, we are getting an incorrect value. Now, while I understand his thinking in dropping the last fill up from the calculation, here is the problem with that:

The last fill up, represents how much fuel you used for that previous tank and the distance you recorded. So that value HAS to be used to be correct. This is why the first tank value has to be dropped. Make sense yet?

So you do not need to drop the last and count the first, just simply don't count the first entry at all, even in the averaging. Then you will be all good. I'm assuming your overall average math is counting all the volumes/costs then dividing by all the mileage or something to this effect.

This is what I did with my excel sheets. I do not factor the volume or cost of the first fill up at all for my averaging.

That should fix this.

Now the only other problems are, using partials a LOT, or missing fuel ups, those will REALLY screw with the averages. If people want accurate tracking, they will be best served by ALWAYS filling their tank full, and always recording the fill up. I have so far for nearly 2 years done this without fail. All of my entries are present, and I have no partials. I will take that back, there was one partial that someone else did, which I corrected to a full tank to keep my figures straight by adding it to the next fill up

Hope the book helps you two..

[pb]

The last fill up, represents how much fuel you used for that previous tank and the distance you recorded. So that value HAS to be used to be correct. This is why the first tank value has to be dropped. Make sense yet?

Yep, I see what you're saying DTMAce. That makes sense to me.

The first tank value is dropped the way we're doing things now. We don't include it at all for odometer trackers in the overall average calculation. (Tripometer trackers are a different story--we can include every fuel-up for them because there is always a distance included with the fuel-up.)

So we're not making any changes at this time. But I get the point about "fuel that hasn't been burned yet" vs. "difference from full for this distance". It might just be two different ways of looking at the same thing.