Wednesday, 10 June 2009

Driving data

It’s been quite a while since I last drove a gas-guzzling car. My little car was chosen for fuel-efficiency and low CO2 emissions. So I thought I would look good when I did my “driving carefully” experiment.

At first it wasn’t difficult to get into the mind-set of thinking ahead, braking less and driving more slowly, and for the most part I did OK. Trouble was, there were a few times when I was late for an appointment and I reverted to my old ways. Also, most of my journeys were relatively short - 10 miles or so – and on roads with roundabouts and traffic lights, which I’m sure contributed to the less than brilliant result.

So – what was the outcome? I filled the car a week or so ago and have driven 304 miles. When I filled up a couple of days ago I put 38.3 litres into the tank.

So on 38 litres of petrol, or 8.36 gallons, I have got about 36 miles per gallon out of the car – hardly a star performance.

Some cars let you see your average miles per gallon as you are driving, and that must be useful. I don’t have that gadget on my car. However I will try and monitor my petrol consumption over the next few tanks to see if I can improve on 36 mpg.

This calculation wasn't particularly intuitive. Looking up how many litres in a gallon wasn’t difficult, but it took some proactive thought. Even the new (in so many senses of the word) Toyota Prius, boasts its fuel consumption as 72 mpg, although they know all their customers will be filling up in litres. If we are going to buy fuel in litres, shouldn’t we measure its performance in litres?


  1. Caroline

    Your always intersting thoughts, prompt a range of thoughts from me from how one reduces consumption (service car regularly, avoid using air con if fitted,keep windows shut , remove roof bars....).to..

    Why stop at litres? why not Kms which I think you find in car brochures now as well? 0-100kph? why have quantity guage at all? what you wnat to know surely is range as a performance measure?

    bet electric cars only have range measure??? evolution maybe?

    Not sure this helps but good to reflect as always!

  2. I think the mixing up of units has a disastrous effect in a whole variety of areas. Not being able to make simple calculations like the mpg because we buy our fuel in litres might not be rocket science, but it does mean the majority don't regularly look and think about fuel consumption. I know I didn't. So, yes, I think you are absolutely right, km and miles, and speed calculations all need sorting out. Thanks for the additional fuel on the fire.