Fuelly is a great site, really helps me keep track of my fuel costs. But there's one major flaw as far as I can tell. Its the fact that it requires a full tank to calculate the MPG's.
This is not a problem for me, one of my cars has a 4.4 gallon tank, the other has a 7.7 gallon tank. But here in the UK, fuel is over $10 a gallon and I cant think of one person in my town, friends or family, that ever fills thier tank when fueling up. On average people just put $15 to $25 worth in at any given time. As mentioned, the main reason being that fuel is expensive and people simply cant afford to fill thier cars, another reason is that cars here are obviously more economical, even two gallons should last around 120 miles in most modern cars. And then there's the odd person that feels filling thier tank is adding weight, therefore affecting thier MPG's. All valid points, but just goes to show, that fuelly cant or wont be used by many people for these reasons.
I can't really figure out any method to get 'short time' FE if you don't fill up your tank. On the long run, little amounts give a valid average too, but you can't compare tanks this way.
Failsafe: If I guess correctly fuelly does the math for the (average of) partial fills too if you fill the tank once in a while.
Me: I must be a geek that I always fill my tanks as full as I can. With my bike it's not a biggie, she has a 4-gallon tank. My car has a 11.9-gallon one, and I fill it too. I'm perfectly comfortable with long lasting tanks (the last time I fueled up the YARDIS was the middle of February) and I don't mind coughing up the price at once: it costs the same, after all. Even if most people seem to feel otherwise.
The cost is the same, once you fill the tank the first time. And unless you have an aircraft-type fuel totalizer, you will never know how much fuel you use unless you fill the tank.
Personally, I don't use Fuelly's cost system, because I don't like having to enter unit cost for fuel instead of total cost.
I have been keeping track of mileage and cost for decades using the simple device of a notebook, writing implement, and calculator. I don't need Fuelly for that. I started using it more as a way of contributing my little bit of data to others. After all, I can browse the data on Fuelly's open site without ever signing up.
Yes but a lot of people dont have the spare money to fill thier tanks in the first place. You're talking $120 for some cars, once the weekly outgoings have been paid, people cant afford to fill thier tanks. As said most people just put a few gallons in at a time.
...and if they lose their jobs they starve to death in a week flat? No reserves, no nothing? For Christ's sake, we're not talking about the poor of the 3rd world... they do have the resources, they should only have a tiny bit of forethought!
Fuel economy can only work calculated if you measure the distance covered and the amount of fuel used. The distance is quite easy to measure on a car with an odometer. But the only way to accurately measure how much fuel is used is to either A) but a measured amount into an EMPTY tank and drive until it completely runs out, or B) full the tank completely and then measure how much fuel it takes to fill it back up again.