I know, it's incredibly sad, but I've kept a record of all the fuel I've used in my car. It's quite interesting in a statistical geeky sad sort of a way :-)

This chart shows the average UK miles per UK gallon achieved over the last 3 years, and a rough mpg calculated for each fill (the car is usually filled to the brim, so the rough mpg is usually as accurate as possible - which is to say frequently quite inaccurate!)

I've marked interesting dates on the chart - My mpg on-track lies between 11mpg (Donington) and 24mpg (Silverstone), with the airfields usually about 15-16mpg. The best true reading was 40mpg while on a long gentle drive around Scotland, although one fill on my way up to my first day at Donington allegedly achieved 41.3mpg (I'd say this was just a spurious result due to an air bubble stopping my fill before the tank was actually full). It appears that my economy drops off slightly over winter, and improves in summer, and after a track day my economy seems to take several weeks to recover!! :-)

The total 3-year average over 33181 miles is 29.6mpg.

A total of GBP £3900.43 was spent on 5124.1 litres (1127 UK gallons), or a cost of 12 pence per mile. I drive an average of 225 miles before I refill the tank (35.09 litres put into my 50 litre tank on average. My largest fill was 46.18 litres, when the fuel gauge was about a mile below "E" - I should have an average range of 320 miles if I were to empty the tank completely before refueling, although the best I have managed before bottling out is 309 miles (on 44.3 litres, which would have given me a full-tank range of just under 350 miles))

Optimax petrol has made no discernible difference to my economy, although the car is happpier and has better throttle response when running on it, so I now fill up with optimax about every 5th time. (I have a normally aspirated car running at the default timing though, so some of the benefits of optimax's higher octane rating are lost on me)

Jason Williams, September 2002