pb
Aug 14, 2009
6:38 AM

First, make sure you click the "UK" link the upper left corner of the page. That will make sure you'll looking at UK units.

So far, you've told Fuelly that you've gone about 292 miles and put in about 8.5 gallons of gas. (Sorry, US units, I know.) If you divide 292 by 8.5 you get 34.4--that's your average fuel economy in US unites. It's 40.7 UK MPG.

When you fuel up, just put in the miles on your tripometer and the amount of gas you just put in. That method works for figuring out your average fuel economy.

Make sure you brim your tank every time (or fill to the same point) and reset your trip - you fill up, reset your trip, then next time you fill up you can note down the miles you got on the last lot of petrol, and assuming you're brimming your tank again you will know the exact amount of petrol you used to do that mileage.

Apart from that, as pb says, make sure you're using UK mode. I thought this site was doing its calculations wrong before I noticed the US/UK modes. Turns out not everything is bigger in the US, gallons certainly aren't!

Looking at your bike's page you got about 57 mpg off your most recent fillup. Looking at your earlier fill-ups, and the fact you put in 13litres on an 80 mile tank, the fill-up before that can't have been a full tank.

For this site to work properly you really need to brim it every time. Try editing your earlier fill-ups to partial ones, I think that should exclude them from your average MPG number.

"When you fuel up, just put in the miles on your tripometer and the amount of gas you just put in." I suppose that was too straightforward to put in the FAQ :p Glad that got cleared up.

I see, I don't brim it every time..will from now on. Thanks guys, very helpful.

pb
Aug 14, 2009
8:43 AM

Thanks Nat, yeah, complete fills are an important part of how the site works. Here's more info: Why do I need to fill the tank?

Wait, wait, wait. This thing couldn't be working right. If I fill in how many miles I got since last fuel up, how many litres I just put in and how much it just cost me per litre, it all seems fine. It gives me a MPG, and there we go. Only, the MPG calculated (for some reason?!) seems to take into account the number of litres *I just put in* -- why would it do that?!

pb
Aug 25, 2009
3:43 PM

yeah, Pryda, that's how it works. If you make that calculation every time you fill your tank you get a good sense of your average mileage. It's not an exact science.

There are probably other ways to calculate your fuel economy, but this is the way we set things up for Fuelly.

Hrm. I knew something was messing with my results but it took a while to put my finger on it. I don't see why the amount of fuel I put in right now affects the performance of my motorcycle in the past. It's illogical, right?

mathowie
Aug 25, 2009
6:27 PM

We measure by difference, assuming you fill up the tank to the brim every time. If you imagine that is a maximum number, 100% (units don't matter in this example) we could every fill up for how many units you used up since it was last at 100%, and figure out how far you went to calculate your fuel economy. It's pretty simple.

If you aren't filling up the tank to full, you should check off the "partial fuel up" option and we won't calculate fuel economy for that specific fuel up, but we will for your cumulative fuel economy (which takes all your distance traveled and all fuel ever burned to calculate a total).

See, it doesn't seem to work that way. It seems to take unburned fuel into the equation too, which is messing with my results.

(I can't edit my post? o.o) Therefore, it thinks my bike has used 14 more litres than it really has. Maybe I'll manually correct this with a 0litre fuel up, if that works.

I just created my account. My car is new. The fuel tank capacity is 55L. I've added the initial fill at 0Km, 55K, then my 2nd fill, 42.3L at 570KM odo. My reading is saying 0L/100Km. What am I doing wrong?

Ignore my previous question... I fixed the issue by changing the initial fill up at the dealer from millage 0 to 5. I suppose the value of the odometer has to be bigger than 0Km.