18 Aug 08
S-Type diesel engine
The superior fuel economy you achieve with diesels is attractive, but a lot of miles have to be covered before the extra premium you shelled out for a diesel model makes sense.
Based on 60mpg for an average diesel supermini and 45mpg for its petrol equivalent, and factoring in the 11% price jump for diesel, the saving over 20,000 miles is a fairly healthy £635. Over 5,000 miles, however, the diesel saving drops to just £159.
Fuel if you think it's over
There are other factors to consider. The extra money needed to finance the car will bump up the interest bill; diesels traditionally need more frequent servicing and the extra weight of the diesel engine (typically 50kg over the petrol) negatively affects handling and increases tyre wear.
According to Paterson, whose job is all about crunching the numbers on cars, there's an easy cut-off point.
'The caveat still remains, you need to be driving about 20,000 miles a year to make diesel work for you over petrol,' he cautions. 'I don't think people are doing the sums. Certainly the lower-mileage diesel drivers are paying more than the petrol equivalent.'
Of course there are other benefits to diesel. The extra torque over a similar petrol makes them feel much stronger and faster on the road even if the power expressed in bhp is actually less. And the residuals are much better. But to think diesel is the default cost-saving, planet-saving option is to live in a fuel's paradise.
