Fiat 500

What are car CO2 emissions?

There’s a lot of talk about CO2 emissions from cars, but what exactly are they? Here’s everything you need to know.

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By Cazoo editorial team

The amount of carbon dioxide – also called CO2 – that your car produces has a direct impact on your wallet. And it has become a political issue, too, as governments around the world introduce legislation to tackle the climate change crisis. But why does your car produce CO2 in the first place? Why does it cost you money? And is there anything you can do to lower your CO2 emissions while driving? Cazoo explains.

Why does my car produce CO2?

Most cars on the road have an engine that uses petrol or diesel fuel. The fuel is combined with air and burned in the engine to generate the power that drives the car. Burning anything produces gas as a waste byproduct. Petrol and diesel contain a lot of carbon and so burning them produces waste in the form of carbon dioxide gas. Lots of it. It’s blown out of the engine and through the exhaust pipe. When it comes out of the pipe, the CO2 spreads into our atmosphere.

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How are CO2 emissions measured?

The fuel economy and CO2 emissions of all cars are measured before they go on sale. The measurements come from a series of complex tests. The results of those tests are published as the ‘official’ data on fuel economy and CO2 emissions.

You can read more about how a car’s official MPG figure is calculated here.

A car’s CO2 emissions are measured at the exhaust pipe and calculated from the amount of fuel used during the tests, using a complicated set of equations. The emissions are then listed in units of G/KM - grams per kilometre.

How do my car’s CO2 emissions affect my wallet?

Since 2004, annual road tax charges for all new cars sold in the UK – and many more countries besides – have been based on how much CO2 the cars produce. The idea being to encourage people to buy cars that produce less CO2 and to penalise those who buy cars that produce more CO2.

The amount of tax you pay is based on which CO2 ‘band’ your car falls into. Owners of cars in the bottom Band A don’t have to pay anything (though you do still have to go through the process of ‘buying’ road tax from the DVLA). Cars in the top band are charged at a rate of several hundred pounds a year.

The bands changed in2017, increasing the road tax charge on most cars. The changes don’t apply to cars registered before 1 April 2017.

How do I find out my car’s CO2 emissions?

You can find out the CO2 emissions of a car you already own and which tax band it’s in from the V5C registration document. If you want to find out the CO2 emissions and road tax costs of a car you’re interested in buying, there are a number of websites with ‘calculators’. In most cases, you just enter the car’s registration number and you’ll be shown the data for that specific car.

Cazoo gives you the level of CO2 emissions and road tax costs in the information we provide on each of our cars. Just scroll down to the Running Costs section to find them.

It’s worth noting that road tax charges for cars registered after 1 April 2017 actually go down as the car gets older. And there are extra charges to pay if the car cost more than £40,000 when it was new. If that sounds complicated, it is! Keep an eye out for the Road Tax Reminder that will be sent to you by the DVLA about a month before your car’s current road tax expires. It will tell you exactly how much your renewal will cost.

What is considered a ‘good’ CO2 emission level for a car?

Anything less than 100g/km can be considered low – or good – CO2 emissions. Cars that produce 99g/km or less, and that were registered before 1 April 2017, owe no road tax. All petrol and diesel cars registered after 1 April 2017 are charged for road tax, no matter how low their emissions.

What sort of cars produce the least CO2?

Diesel cars produce a lot less CO2 than petrol cars. That’s because diesel fuel has a different chemical makeup to petrol, and diesel engines burn their fuel more efficiently.

Conventional hybrid cars (also known as self-charging hybrids) generally produce very little CO2 because they have the capability to run on electric power some of the time. Plug-in hybrids have very low CO2 emissions because they have a much longer electric-only range. Electric cars produce no carbon emissions, which is why they’re sometimes referred to as ‘zero-emissions’ vehicles.

How can I lower my car’s CO2 emissions?

The amount of CO2 your car produces is in direct proportion to how much fuel it uses. So making sure your car uses as little fuel as possible is the best way of reducing its CO2 emissions.

Engines use more fuel the harder they have to work. And there are loads of simple hacks to avoid making your car’s engine work hard. Keeping the windows closed while driving. Removing empty roof racks. Keeping the tyres pumped up to the correct pressure. Using as little electrical equipment as possible. Having the car properly serviced on schedule. And, crucially, accelerating and braking gently.

The only way to lower a car’s CO2 emissions below the official figures is by fitting smaller wheels. A Mercedes E-Class, for instance, with 20-inch wheels will emit several G/KM more CO2 than it would with 17-inch wheels. That’s because the engine has to work harder to turn the bigger wheel. But there may be technical issues that prevent you fitting smaller wheels – the size of the car’s brakes, for instance. And your road tax bill wouldn’t go down, unless you were able to get your car reclassified.

An easier way to find or sell a car

You’ll find lots of used cars for sale at Cazoo, all available to buy through our trusted dealers.

Cazoo makes selling a car just as easy – just enter a few details for an instant online valuation. If you accept the offer our partners will get in touch to arrange payment and collection of your car at a time that suits you.