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Diesel v Petrol: the choice is narrowing

Diesel or petrol? Why, diesel, of course. It is greener; it has lower CO2 and, as we’re both told and financially incentivised, less CO2 is better for the environment. All you need to do is select the lowest CO2 car you can and you’re fine, right?

If only it were that simple. Let’s not get into the debate about particulate emissions and NOx levels here: that’s a debate that’s going in motor manufacturer technical departments right now, and the sleepless nights caused is keeping many an energy drink manufacturer in fine style.

No, it’s the simple skew in efficiency comparisons that have seen diesel score over petrol up to now, thanks to multiple billions of pounds of investment in perfecting common-rail, direct injection, trick turbos, injectors more precise than medical instrumentation and so forth. As I’ve discussed before though, petrol’s catching up, fast.

Indeed, models such as the new Mazda6 show it arguably already has caught up. The new 2.0-litre SKYACTIV-G, arriving here early next year, emits 129g/km CO2; yes, the diesel emits an even lower 108g/km, but the petrol is still 10g/km cleaner than a Mondeo diesel, still dips below the crucial 130g/km barrier that’s to become so important in coming years – and also, most significantly, costs less than £20,000.

Here’s one of the things with modern diesel – they’re very fuel efficient and appealing, but you don’t half have to fork out for the privilege. The old convention had diesel costing £1,000 more than petrol: today, it’s up to £1,500 and may stretch even further in future years as Europe clamps down on particulate and NOx emissions.

Some manufacturers reckon the only way to deal with NOX is ‘expensively’. And it’s the customer that’s going to have to pay for this pricey exhaust after treatment. Whenever you see mention of Euro 6, it’s safe to assume that diesel engine won’t be a budget unit…

Foto: Hildebrandt/Lorenz

Mazda’s SKYACTIV-G engine is different, though. Because petrol cars don’t need such onerous exhaust after treatment gear to clean up their tailpipe emissions, and because non-turbo petrols are relatively simple and inexpensive to build, it’s able to offers the car at a much lower list price, one that expensively-optimised eco specials can only dream about. Superminis costs £20k these days, not large four-door saloons…

And the added bonus of this low list price/low CO2 combination? Benefit in Kind rates that will have recession-hit owners (or companies) saluting. At £52, the 2.0 145 SE is £12 a month cheaper than another green low-CO2 car, the £25,730 BMW 320i EfficientDynamics. For higher rate taxpayers, it’s even better: £104 vs. £128. Who wouldn’t like to have nearly £300 a year more in their back pocket?

Things are even starker when you compare the Mazda with that current junior exec green star, the BMW 320d EfficientDynamics (the diesel alternative to the petrol ED above). It costs £140 a month for the higher rate taxpayer, with a £28.080 list price easily outweighing the car’s 109g/km CO2 emissions. The ‘green’ saloon BMW is thus £36 a month more expensive than the ‘thirsty’ saloon Mazda. It’s enough to make you green with envy.

Mazda6 2013

It’s beginning to look like petrol has the opportunity to save company car drivers money, thanks to going on its own green economy drive. When a main deciding factor for a company car IS saving money, Mazda could well be starting a trend here – the slow shift back from fleet diesel monopolization over to the more even balance seen in the retail sector.

Mazda Head of Fleet Steve Tomlinson spells out how dramatic the shift to diesel has been: “Diesel models account for approximately 90 percent of upper medium sector company car sales”. He says this is because many drivers are clocking up high annual mileages, which of course is true. But it’s also down to the fact too many petrol engines have topped 140g/km CO2, even 160g/km CO2, making choosing them financial nonsense.

He continues to say “there is a section of the company car driving population that require an upper medium sector car to meet work or lifestyle requirements but do not drive quite as many miles.

“Consequently, we believe that the all-new petrol-engined Mazda6 offers the perfect choice as employees can enjoy the car’s top-notch performance whilst benefiting from tax savings versus competitor models.”

It’s this final point that I’d say is the clincher: petrol might not offer the high-torque performance of a diesel, but it does provide clear expenditure savings by itself lowering CO2 – and in a recession-pressured country eager to eek out any savings possible, this could lead to a gentle switch back to petrol for some.

Tomlinson agrees: “The all-new Mazda6 will shake-up the upper medium company car sector. Although diesel power will dominate corporate sales, we believe petrol-engine models will secure a significant following.”

After all, it’s a much better engine. It has 21% more power and, even more significantly, a 27% increase in torque. Economy is improved by 22% (to 50.4mpg!) and CO2 is down by 17%.

It also provides a route out of diesel for that minority of people who still don’t ‘do’ diesel and still yearn for a petrol. For them, there is no choice: petrol every time – it’s just that they’ve been forced into diesel. No more. Watch the Mazda6 sales split with interest, for there could be a story to tell here…

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Richard Aucock

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