i found the best way, to judge my milage, (bearing in mind i live in the smoke) is what i get to the pound, until recently due to fuel prices going up, i was getting 50 miles to the tenner, now thats down to just over 45 miles to the tenner, and thats what i would call around town driving, i always set trip meter, its a good indication on how your doing. so its just less that 20p per mile.
on a run i get around 15p per mile, which considering our trucks are like a brick going through the air, plus there weight and the larger tyres we carry. all in all i had the cavalier which gave same milage roughly around town, but down to 10p a mile on a run, and it had smaller tyres, cut through the air better.
so my advice to check if your on the right side, is, as fuel gauge light comes on, stick a tenner in, press your trip meter, and when fuel light comes on, take a reading, do this a couple of times, and you will see what your getting.
Just remeber, you wont get the same as saloon car on a run, the fronty has the same shape as a brick, but drives like a feather.
sean