Totals KM tracked and MPG computation

[mauricetan]

Hi.. I just wanted to ask regarding the "total km tracked" .. When i do partial fill ups.. why does it add all the kilometers for every partial fill up? Isn't it better if the "total km tracked" is just the full fill up? So it would actually be able to track it more accurately.

The computation for the MPG is the final kilometers since last fuel up reading divided by all the liters combined from the partial fill up + the final fill up?

I just inputed 2 partial fill up before my final fill up on my minivan and it won't show me my actual MPG

[mauricetan]

Also, if it's a partial fill .. the kilometers since last fill up should be able to leave it blank since it's only a partial fill up.. the kilometers last used data should be from the next full fill up so that it would be able to compute the MPG more accurately.. the kilometers since last fill data would be divided with all the total liters from all the partial fill up + the full fill up...

Just saying that sometimes not everyone can or would want to fill up fully right away

[pb]

First, take a look at: Why doesn't my fuel-up have a calculated MPG (L/100km)?

Fuelly needs a full tank to work from because it calculate an individual fuel-up MPG using the difference from full since your lat full fuel-up. Without a full fuel-up to work from, Fuelly can't calculate an individual fuel-up MPG. Here's more about that: Why do I have to fill the tank all the way up every time I buy fuel?

When Fuelly calculates your total average MPG, it uses your total distance driven and total fuel volume filled. Fuelly doesn't do a simple average of your calculated averages. That way it can includes partials in your overall average. And that's why it makes sense to use partials in your total km tracked. Those partials fuel-ups are tracked for your overall average.

[mauricetan]

Thanks!

I actually did 2 partial fill up then filled up on my minivan.. but after inputing the final fill up... it didn't give me any MPG information? Why is that?

So with fuelly its better to fill up completely and avoid partial filling up?

Is it better to use odometer tracking if i always do partial fill?

[mauricetan]

Also when you said total distance driven.. How would that work if i have like 2 - 3 partial fill ups in between ?

Normally.. if the gas is a bit expensive and i need gas... i usually fill up like $20-30 bucks then fill up after a few days when the price is a bit cheaper..\

Is there a way to have more than 1 input for liters and price when adding a fuel up ? So it would be able to track the gas spending more accurately? So instead of adding 3 fuel up with 2 partial fill.. just add one fuel up then input the partial fill and price on each line and there's gonna be only one "last kilometers driven since last fill up"

[MMUK]

>So with fuelly its better to fill up completely and avoid partial filling up?

Yes

Partial fill-ups gain you very little or nothing in real life. Yes you may save a few cents due to price fluctuations, but the extra visit to the station will probably cost you in terms of time (and money if the station is off your normal route).

[pb]

If you do a lot of partial fuel-ups you might get pretty frustrating with Fuelly, yeah. Take a look at the FAQ I linked about filling up to full.

...it didn't give me any MPG information? Why is that?

Fuelly needs a full tank to work from. Your first two fuel-ups were not full, so there's no way to get the difference from full to give you an individual fuel economy calculation.

Also when you said total distance driven.. How would that work if i have like 2 - 3 partial fill ups in between ?

Just keep in mind that there are two types of fuel economy calculations happening at Fuelly. There are individual fuel-up calculations and your overall average calculation. They each use a different method of calculation. Individual fuel-ups use the distance between two full fuel-ups, and the fuel used to get back to a full tank. So if you have any partials at all, you won't get an individual calculation for that fuel-up or the next one. Because Fuelly needs two full fuel-ups in a row to get individual fuel economy numbers.

For your overall average, Fuelly uses total distance driven and total fuel filled. There's no need to know your tank size or the difference from full there. So it can use all of your fuel-ups. You could add all partials and you'd still get an overall average fuel economy number.

So with fuelly its better to fill up completely and avoid partial filling up?

Yes. If you add a lot of partials you might find Fuelly a frustrating experience because you won't get many fuel economy numbers along the way. You need two full fuel-ups in a row to get any individual fuel-up fuel economy calculations.

[mauricetan]

Understood! Thanks! Would using the odometer tracking be better if i have partial fills in between?

So is there no way for fuelly to be able to fix or update its calculation and be able to allow partial fill? Cause the only way i see it is i would use the Final kilometers driven and add all the liters of all my partial fill up + full fill up.. this is the only way for it to work in my opinion.. this would be able to keep track of my MPG/Fuel mileage but the only downfall would be the $ spent on filling up won't be accurate since every partial fill up would have a different pricing...

So there's no work around for partial fill up?

[MMUK]

>So is there no way for fuelly to be able to fix or update its calculation and be able to allow partial fill?

I did make a suggestion about aggregating partial tanks together with the next full tank which would have permited an mpg figure to be calculated, but that does not fit in with their 'one tank - one mpg figure' philosophy.

I only have one partial tank (an attended station - they did not let me fill the tank myself) - I added it to the next tank, so on fuelly it only shows as a single, full tank with an extra large size. Seems to work fine apart from screwing up the 'max miles from a tank' and 'max fuel volume' figures.

[pb]

So is there no way for fuelly to be able to fix or update its calculation and be able to allow partial fill?

We don't see Fuelly as broken. If you start adding partials together you're aren't going to get an accurate calculation because the *difference from full* isn't using the correct tank size. Your calculated fuel economy for those fuel-ups are going to be significantly off in some cases. We feel it's better to be as accurate as possible when we show any fuel economy numbers to people.

This method of tracking isn't rocket science. We're not measuring every drop. So there's going to be messiness here and there, but we feel like combining partials is too messy, even though it would be more satisfying for our users. It's great to get the feedback of numbers, but we don't want to be misleading for the sake of satisfaction. We also know this means not everyone is going to be able to use Fuelly, and that's ok. I'm sorry if it doesn't work out for you, but we feel like our current system is the best way to handle partial fuel-ups without misleading people.