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Assessing the merits of so-called super fuels
Most fuel brands offer “premium” or “super” unleaded petrol or diesel that they claim improves your car’s performance and helps to protect your engine, while cutting your fuel consumption.
However, with these souped-up fuels costing up to 10p more per litre than standard, the question is whether they are worth the extra outlay?
We wanted to know. So here are the results of our investigation into exactly what benefits super/premium fuel is supposed to offer, and whether it delivers on those promises.
As a rule of thumb, it's generally 'super' for petrol and 'premium' for diesel.
Premium fuel is more expensive than standard due to its higher research octane number (RON) - the benefits of this increased octane rating include lower fuel consumption as well as better engine protection and performance.
In the UK, standard unleaded now has a RON of 95, while super unleaded is around 98 RON.
Some petrol companies also market a top-of-the-range fuel with a RON of 102.
BP said of its premium fuels: “BP Ultimate fuels help your engine to run at its most efficient, so as little precious energy as possible is wasted – helping you get more miles from your tank.”
Shell argues that its V-Power Nitro+ fuel, which is available in unleaded petrol and diesel versions, has a unique, dual action formula designed to clean and protect vital engine parts to “make your drive feel alive”.
According to petrolprices.com, the typical price of a litre of unleaded petrol is currently around £1.28 per litre, with super unleaded costing around £1.35 per litre.
Diesel drivers can expect to pay £1.32 per litre of standard fuel, and £1.40 per litre of premium.
The higher octane rating of super or premium unleaded fuel should make it work more efficiently, thus delivering more power for less fuel burned.
But while some drivers report noticing a small increase in the numbers of miles they can do before refilling the tank when using premium fuel, others find that there is very little or no difference. It seems to depend on a range of factors such as how and where you drive and what type of car you have.
The best way to discover if premium fuel can help to reduce your consumption is therefore to fill up with it, say, three times and see if you notice any difference.
If not, you’re probably better off sticking with regular fuel – especially if saving money is your main aim.
As with consumption, the increase in performance you can expect with super or premium fuel will depend on the car you have, the way you drive it and what sort of journeys you go on.
Higher-octane fuels suit high-performance engines where pressures and temperatures are greater and it can therefore be used to boost the amount of available horsepower and improve performance.
Regular engines, on the other hand, do not come with the same compression ratios and engine temperatures as turbocharged and supercharged engines, meaning they get a lot less out of the high-octane characteristics of these fuels.
Generally speaking, owners of higher-performance cars will get the most out of premium fuel as a result – especially if they are often driven hard on open roads.
But drivers of vehicles with smaller engines that are used for little more than local errands and the weekly shop are unlikely to see any significant benefit.
Higher-octane fuels help to prevent so-called ‘engine knock’, which is when unburned fuel pre-ignites in a vehicle’s engine, often damaging interior components.
The higher the RON of a fuel, the more likely it will be to burn in a controlled manner in the engine, thus lowering the chance of ‘knocking’.
Again, however, only motorists with high-performance cars – where engine knock is more prevalent due to the higher compression ratios caused by superchargers or turbochargers – will really see the benefit.
BP said: “BP Ultimate Unleaded is formulated to protect against wear in key engine components and guard against the harmful effects of corrosion. Plus it contains a special formula designed to lower the friction in your engine.”
Premium or super fuel also has additives that help to keep your engine clean, which should mean that it keeps working for longer.
Esso said: “Our premium grade, higher octane petrol has double the detergent additives to help give a deeper clean for better engine performance.”
Whether you're buying premium or regular fuel, the cost-per-litre can vary significantly from forecourt to forecourt, but driving that little bit further for cheaper fuel could mean you're actually spending more money to get there than you save at the pump.
Our handy Fuel Cost Calculator will help you work out if your search for cheaper fuel is actually costing you more…