Ever wondered what a trip to the shops costs? Worried how much money you burn in traffic? And do you know your car's real MPG figures?
You might know your own car's fuel efficiency figures. They were the numbers posted on the windscreen at the car dealer (along with the price and monthly repayments, of course).
You might have noticed that one figure told you miles per gallon on an urban cycle, another miles per gallon on an extra-urban cycle (whatever that means) and a third telling you your combined MPG.
But what do those figures actually tell you? Those figures are conducted indoors on a rolling road within defined temperatures and controlled speeds. It's all very scientific, but it doesn't say much about your real-world fuel use.
So, armed with a sensible supermini* and an electronic gizmo that reads data from the engine's fuel management system, we set our own real world tests. We filled up on fuel and asked the gizmo to tell us how much each of our ordinary journeys cost.
Real-world scenarios
1) A 5-mile round-trip to the supermarket
If you don't drive to and from work then, chances are, the trip to the supermarket is the most regular journey you take. We drove a round-trip to the supermarket starting from exactly 2.5 miles away to make an nice, round 5-mile trip on flat, urban roads.
Cost of journey was a surprisingly reasonable £0.20 - not much more than the cost of buying plastic bags (we forgot them, again).
2) Shopping around for fuel
Does it really make sense to shop around for fuel? Or should you just fill up whenever you get the chance? Our trip from one fuel station to another was 1.7 miles (so we cheated and drove on a further 0.3 miles to make it a nice, round 2 miles).
Cost of journey was £0.11, using 0.087 litres (so a four-mile round-trip would cost £0.22).
Say the nearest fuel station sells unleaded at £1.04 per litre. And the second fuel station (a four-mile round trip away) sells it at £1.02 per litre. If you buy twenty litres of fuel you will save £0.40. But once you factor in the four-mile round trip, you're only £0.18 better off (and you've wasted 10 minutes of your life).
Is it worth it? How much is your time worth? We bet it's more than the £1.08 you save for every hour you spend driving around for cheaper fuel. Unless you know a station that sells fuel at a price that's considerably cheaper than average.
3) Visiting a friend
We popped round to visit a friend who lives in the green belt. It's an opportunity to have a little blat on twisty roads, a 6.4 mile round-trip from the by-pass that takes in hills, bends and a few miles at the national speed limit.
You don't get to use the throttle much, living in the city. So a country road can be a good excuse to get the right foot twitching.
We drove the same journey twice. First we drove it impatiently, getting high revs before changing up, braking at the last moment and driving purposefully.
Next then did the same drive but frugally, changing up as soon as possible, trying not to go beyond 2000rpm at any point, coasting downhill and anticipating the need to brake.
The difference was quite significant: Cost of journey was £0.20 when driven with economy in mind, or £0.32 when driving in a big rush (still legally, of course).
4) Idling at the drive-In
We all want to eat a healthy balanced diet. But the temptation of a thick shake, mega-sized fries and a burger with all the trimmings is enough to get us in the car and queuing at the drive-in. But how much do you spend queuing for five minutes for your grease fix?
Cost of idling was £0.01 (and it took a further one and a half minutes to take it up to £0.02).
But beware of air-conditioning. It is said that air-con will cut your fuel economy when driving by 10 per cent. But when you're idling it's considerably more than that.
Cost of idling with aircon-on £0.02 (and it took just 14 seconds longer to reach £0.03). So the lesson is: windows down, aircon-off when idling or in heavy traffic!
How do you test your fuel economy?
If your car doesn't have a fuel economy gauge, or you don't have access to the kind of gizmo we used for this test, don't worry – a little bit of simple maths is all you need to work out your fuel consumption.
If you're an organised sort, you'll keep all your receipts and MOT certificates. So there's a very simple way of finding your annual average cost-per-mile?
Find your MOT certificates and take one odometer reading (the mileage) from the other. If your 2009 certificate says 49,325 miles and your 2008 certificate says 36,897 you have travelled 12,428 miles. Now tot up the fuel receipts you've collected over the year and divide that total by the total mileage (in our case 12,428). And the number you come up with is your average cost per mile.
Working out your average fuel economy is even easier. Fill up your tank to the brim next time you need fuel. Set your trip meter to zero (it's on your dashboard, usually next to the odometer). Next time you fill up, note down your trip computer reading and exactly how much fuel you needed to fill the tank.
Your average fuel economy in MPG is found by dividing the distance driven by the fuel used. So if you've used 12 gallons of fuel and driven 412 miles, you divide 412 by 12 to get a figure of 34.33 mpg.
* Notes on our test: Our test was conducted on real-road conditions using a 2008 Mazda 2 TS2 with a petrol engine. The fuel usage meter was programmed to indicate the cost of driving based on a per-litre cost of £1.04.
Related links
Dr Brace's amazing fuel diet
Top 10 fuel guzzlers in the UK
