Fuel economy explained

When you are looking at new cars and you are reading the top tips to finding a new car, you might come across people telling you to look at the fuel economy.

But, what does it mean? And how does it work?

In this article, we look at what fuel economy is, how it works, and why it’s important when looking at a new car.

What is fuel economy?

Firstly, what do we mean when we talk about fuel economy?

Fuel economy, or fuel efficiency, is essentially how far you can travel on one tank of fuel. The further your car can travel on one tank of fuel, then the better the fuel economy.

It’s the main way people can tell how much they are going to spend on fuel while they are driving their car.

What is the difference between fuel economy and mpg?

There is no real difference between fuel economy and miles per gallon (mpg). It’s just a different way of talking about the same thing.

So, for example, when we talk about miles per gallon, it’s how many miles you will be able to do if you put just a gallon of fuel in your car. Miles per gallon is just another way to talk about fuel efficiency.

How is fuel economy calculated?

The fuel economy figures that you see in reviews and on websites have been taken from laboratory test results. Most fuel consumption figures are measured using the New European Driving Cycle (NEDC) which test the car in different scenarios. The four categories are;

  • Urban fuel economy
  • Extra-urban fuel economy
  • A combined figure
  • Carbon Dioxide emissions

We will go into more detail about these categories below. All cars are tested in air temperature between 20 and 30 degrees and all engines are started from cold.

Urban Cycle

This test mimics town or city driving. The test consists of accelerating and decelerating slowly up to speeds of 9, 15 and 20mph. This is repeated for around 780 seconds, or 13 minutes, during which the car will have driven around 2.8 miles in this environment.

Extra-Urban Cycle

This test is designed to mimic driving on country roads and motorways. The car will gently accelerate to 43mph, maintain the speed for 50 seconds, drop down to 30mph for 69 seconds and then accelerate back up to 43mph.

Combined Cycle

This test is done by calculating the fuel consumption during both Urban and Extra-urban cycles run consecutively over around 6.8 miles.

How reliable are fuel economy figures?

As we said, these tests are done in a controlled environment and don’t consider other external factors. These external factors include;

  • Weather, road and traffic condition
  • Vehicle condition
  • Your personal driving style

So they don’t take those into consideration which can greatly affect the fuel economy. Therefore, official figures should only really be used for comparison purposes when you are looking for cars. Not all cars will be able to return their advertised fuel economy figure regardless of whether you are driving in perfect conditions.

What counts as good fuel economy?

The higher the mpg, the better the fuel economy. However, as a general rule 60mpg is a very good sign. There was a point where just 30mpg was considered great,  but now cars can do triple that. So if you’re looking for a car with good fuel economy then anything above 60mpg is a good place to start.

Petrol vs. Diesel; which is better for fuel economy?

A debate that rages on in the automotive industry is which is better for fuel economy, petrol or diesel.

For a long time, diesel was considered more economical than petrol cars. However, this is no longer the case and they are pretty much even. However, they are best suited to different types of driving.

Diesel cars are better suited and achieve better fuel economy when doing long distance, motorway driving. If you mainly drive around the city and spend a lot of time in traffic, then you won’t achieve the best fuel economy.

Petrol cars, on the other hand, are better suited to city driving and you will achieve better fuel economy in the city than you would on the motorway.However, if you really want the best fuel economy, then you will want to look at a hybrid or a plug-in hybrid. This is because not only do you run on fuel but you also run on electricity. This means that you not only have fuel to run on but you also have electricity which means you can get even further on a tank of fuel. So if you’re basing your decision on fuel economy, then you will want to look at a hybrid or a plug-in hybrid.

When it comes to petrol or diesel, then it really depends on what type of driving you are doing. If you are doing a lot of motorway driving then you will get better fuel economy out of a diesel car.

What are the best cars for fuel economy?

So, what are the best cars for fuel economy? Here are the most economical cars of 2017;

Peugeot 208 1.6 BlueHDi
Peugeot 308 1.6 BlueHDi
Nissan Micra 1.5 dCi
Renault Clio 1.5 dCi
Ford Fiesta ECOnetic
Hyundai i20 1.1 CRDi Blue S
Citroen C4 1.6 Blue HDi Feel
Vauxhall Astra 1.6 CDTi 16V ecoFlex
Ford Focus 1.5 TDCi
MINI One D Hatchback

All of these have an mpg of above 80, with the Peugeot 208 achieving an mpg of 94.2. Again, these are laboratory results and you may not be able to achieve these figures in real time.

What are the worst cars for fuel economy?

We’ve listed the best, what about the worst?

Land Rover Discovery Sport
Audi A4
Volvo XC90
Fiat 500X
Mini Hatchback

So there’s quite a mix there, some are bigger cars and others not so much.

In conclusion, fuel economy is essentially how far a car can travel on one tank of fuel. It is the same as mpg, just a different way of describing it. The higher the mpg or the fuel economy, the better. In terms of petrol vs. diesel, it really depends on what type of driving you are doing. If you are doing motorway driving and long distance driving then you will achieve better fuel economy in a diesel car. Alternatively, if you are doing lots of city driving then you will get better fuel economy with a petrol car. That said, if you want a really high fuel economy, then you might want to look at a hybrid or a plug-in hybrid.

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