28 June 2013 by Gareth Evans Last Updated: 19 Jul 2013

  • Our A-Class is returning rather impressive fuel economy
  • We find the difference between cruise control and human control
  • Trip computer reporting extremely close to claimed mpg

Since I got married a few months ago I’ve really begun to notice the running costs associated with my Mercedes A-Class.

In fact, I’ve taken to driving like the proverbial Miss Daisy in an effort to cut down on trips to the filling station. I do a lot of miles, so it has a big impact on my monthly finances.

On a recent run down to Heathrow Airport I decided to monitor my fuel consumption closely to find out just how economical this car is. I didn’t want to cheat the system by pulling all of the ‘hypermiling’ tricks I know out of the bag; I once won an economical driving competition through a cocktail of methods which while effective, do tend to annoy other road users and in some situations could be deemed unsafe.

What I really wanted was an accurate portrayal of the car in the real world, so my tactic was to drive sensibly while making what I consider decent progress.

I decided I’d try two tactics to see which worked best – using cruise control or driving the car ‘manually’ using my right foot to control speed. Conventional logic dictates that the latter should be more efficient, but I wanted to see for myself.

Setting the cruise to motorway speeds was my basic plan, but I knew this would only work for parts of the journey. On the jaunt down the A1 there are various speed limits, several roundabouts and of course there’s other traffic to contend with on the predominantly twin carriageway road.

So with a blend of constant speed, slowing to a stop and variable speeds through traffic, what did the car achieve? According to the trip computer, which helpfully calculates the fuel economy from the start of your journey, my 94-mile trip at an average speed of 60mph saw fuel economy of 58.8mpg.

That’s not bad at all considering the claimed fuel economy is 62.8mpg – usually the difference between claimed and real-world fuel economy is significantly more.

In terms of range, the car now claims to have 373 miles left and just over half a tank so if more journeys like this are on the cards then the tank is going to contain over 600 miles worth of diesel.

Now, fuel economy like that is quite an impressive feat for most modern cars, but what I’m most impressed with is the fact that not only is my Merc frugal but it’s fast too. There’s a huge chunk of mid-range torque on tap, which makes the car feel like a properly rapid hot hatch.

One thing I am interested in is the ‘Eco display’ on the trip computer. When using the cruise control it seems to think I’m not driving correctly. Sure, the ‘smooth driving’ bar is at 100%, but the other two – ‘acceleration’ and ‘coasting’ – are never close to half way.

I suspected I may be able to do a little better by not using the cruise control and employing some careful right foot instead.

Sure enough, I managed to hit 94% using my right foot on the journey back from the airport, but a quick flick over to the fuel economy screen showed I’d actually managed exactly the same fuel economy as when using cruise control. Obviously this test wasn’t carried out in laboratory conditions, but if there’s a difference between the car’s fuel economy with cruise control compared to driving it yourself, it’s probably too small to decipher.

Current mileage: 5,920

Average mpg: 58.8mpg (ind.)