Driving in an MPG Marathon

Driving greenly – it’s big news. The methods of thrifty driving are fairly well understood: dainty foot on the throttle, think ahead and avoid the brake pedal, get into top gear asap and so on; you can do it pretty easily for a few miles. But what’s it like to drive super-economically for hundreds of miles?

Those who take part in the annual MPG Marathon competition probably know better than most. It’s leg-achingly hard work, with little to show for it at the end, other than a fuel gauge that hasn’t moved much, and a prize if you’ve done better than the rest. What is surprising to many drivers who have not taken part in economy competitions is that the ‘official’ figures for combined consumption can be beaten. But to better them takes some doing.

Traditional thinking on econo-driving did not always mesh neatly with the Highway Code. In the far-off days when carburettors ruled our lives, common sense told one that it occasionally made ‘fuel sense’ to coast on long downhill stretches; the rationale being that it was far better to idle the engine than have it in gear when it would turn faster and also slow the car. These days many cars are ahead of that game, for on lifting off the throttle with the car in gear the fuel supply will be cut, so in that state the car is using zero, whereas putting it in neutral and coasting will use some fuel as the engine is idling. The downside is that the transmission drag will indeed be slowing the car, so there are those who argue that you’re still better off coasting, but as every Green-Car-Guide reader will know, that’s no state to be in, for you don’t have full control over the car unless it’s in gear.

In case any entrants were inclined to go even further and coast with the engine switched off (which needless to say is for a host of reasons mightily dangerous), one of the sponsors of the event – Quartix Ltd – had fitted all cars with one of their GPS vehicle tracking systems that also detect ignition state. So in addition to checking on every car’s real-time movements with the GPS they were aware of whether the engine was on, and any coasting with the engine off would result in expulsion and, rather more vitally, complete ignominy.

These extreme measures are not of course what anyone would seriously contemplate in their everyday motoring. However, many of the routes to green driving on the shopping trip, the school run or the weekend jaunt remain the same as they always were:

Tread carefully on the throttle and accelerate gently

Don’t rev the engine hard

Look and think well ahead

That last one is a real must. How often do you see motorists accelerating until their bonnet is almost on that red traffic light that they should have noticed long ago. The resulting wasted fuel and brake pad wear could have been averted if they’d lifted off much earlier, and indeed the arrival at the red light might have been sufficiently delayed to have allowed it to turn green, so no need to touch the brakes at all. Thinking ahead is not only safe driving practice, it gives passengers a smoother ride and saves fuel too.

The three mantras mentioned above can these days be expanded with less obvious ones pertinent to today’s motoring. Stopped at one of the multitudinous road works for example, turn off the engine if you expect to be idling for more than a few seconds; it’s what some of the latest fuel-efficient cars do automatically. Equally important is the air conditioning – turning that off saves litres of fuel, and the smaller the engine the larger the proportional effect.

You can read all about the Marathon in the News section of Green-Car-Guide, but our own experience of this year’s event in a Skoda Roomster diesel demonstrated one thing that owners of cars with trip computers should bear in mind. The computer’s figures for our two days of motoring were 76.3 and 82.1mpg, but both the Marathon result, and tests of the same car by an independent observer with highly accurate equipment for measuring fuel flow, proved we hadn’t done nearly as well as that! Best use for the computer is therefore to check relative consumptions – your good driving days compared to your lead-booted ones. The real consumption figure may well be 10% or so adrift of what the computer is telling you.

by Peter Cracknell