Motoring Advice

How to choose between petrol and diesel

Apr 30, 2018

How to choose between petrol and diesel

With emissions laws becoming ever tighter and our choices of motive power in cars becoming ever-more-varied, what with hybrids and EVs and so on, you might think the age-old debate of ‘petrol versus diesel’ is becoming something of a moot point. But, despite car companies falling over themselves to get us to a zero-emissions motoring future, the fact of the matter is that petrol and diesel cars still make up the majority of new vehicle sales here in Ireland.

In the recent past, diesels have been king in terms of Irish new car sales. In 2008, diesel – for the first time ever – overtook petrol as our preferred fuel of choice, accounting for 51.7 per cent of the new car market. And, from that point, the black fuel increased its stranglehold on petrol, to the extreme that by 2012, fully 81.5 per cent of new cars sold in Ireland were powered by diesel.

The reason for this is simple: Europe-wide legislation to clamp down on emissions became focused on CO2 emissions above all else, and diesels emit considerably less CO2 than a petrol car of the equivalent power and price. Thus, with our tax laws financially favouring anything that emits less than 120g/km of CO2 (Band A4), diesels became a popular choice.

But diesel has been on the decrease since 2012, with early sales figures for 2018 indicating petrol has an almost 40 per cent market share once more. Why? Well, because after the Volkswagen ‘Dieselgate’ scandal of 2015, authorities began looking closely looking at tailpipe emissions and the veracity of economy claims under New European Driving Cycle (NEDC) testing – and found that NEDC figures are wildly optimistic, while diesel cars emit far more harmful NOx gases than petrol vehicles; no matter how low their CO2.

Now, while diesel is not the evil fuel some sources in the media make it out to be, nevertheless mud sticks, as the old phrase goes, and consumer confidence in diesel-powered vehicles has taken a hit – not least because forthcoming legislation might penalise drivers of diesel cars that are not EU6 compliant, or – in simpler terms – most used diesel vehicles. Couple that to huge advances in efficiency and driving manners on downsized, turbocharged petrol engines with three or four cylinders, and it looks like diesel’s days are numbered.

But which should you choose? Well, here are some simple rules: if you regularly do more than 20,000km a year, or you’re a lazy driver who doesn’t like to change gear a lot, or you regularly tow a fully-laden horsebox, go for a diesel – the long-term economy gains will be fiscally beneficial at such mileage and diesel cars have a lot of torque, meaning you don’t need to stir the gearbox to make them go fast and they can lug very heavy loads too; but if you’re a low-mileage driver, or you’re buying a small car (like a supermini or tinier) as a mere urban run-around, or you’re in any way nervous about global governments doing a volte face on diesel and slapping the fuel with various tax penalties, then opt for petrol. A nice three-cylinder, 1.0-litre turbocharged engine will be both frugal and lovely to drive, so you can’t really go wrong.