How we test cars

Our lab and road tests allow us to thoroughly assess each car and give our verdict on all the things that really matter to car owners.

From overall handling to how accurate manufacturer fuel efficiency or electric-car range claims really are, we put every car through its paces.

We’ve been testing cars since 1962, so we’re well versed in what makes a good one. We review around 100 cars each year, conducting hundreds of individual tests on each one.

Our tests are completely independent, and our verdicts are never for sale. If a car falls down in the most important areas, it will be a Don’t Buy.

Plus, our annual reliability survey enables us to incorporate feedback from tens of thousands of car owners. This means we can tell you what a car's like to live with and reveal the most (and least) reliable cars.

Whatever your needs, you can trust our unique independent testing to tell you everything you need to know when choosing your next car.

Find out which cars excelled in our tests in our round-up of the best cars

Which? car testing

Click the links below to find out more about each set of tests.

• Reliability
• Safety
• Efficiency
• Emissions
• Comfort and practicality
• Ease of driving
• Performance

Best electric cars: discover the EVs that aced our tough lab tests

Reliability

Every year, tens of thousands of people tell us about the cars they own in the Which? car survey.

Through this survey, we learn about a car’s common faults and overall owner satisfaction. Based on the results, we give reliability scores covering three age groups (0-4, 5-9 and 10-15 years). 

The information you give us also helps us track any issues, such as potential problems with specific models.

Any car we know to be unreliable (with a reliability rating of two stars or less) can't be a Best Buy.

Safety

We factor a car’s Euro NCAP rating (when it has been tested by the crash safety organisation) into our scores for each car we test.

We also conduct our own hazard-avoidance and stability tests to identify cars that may leave you in a dangerous situation for longer in the event of an emergency.

Euro NCAP

All cars tested by Euro NCAP are given an overall star rating out of five. If a car tested by Euro NCAP gets two stars or less, we make it a Don't Buy, as we believe modern cars should earn at least three stars to be considered safe. Only cars that score four stars or more are eligible to be Best Buys.

When two star ratings are available for a car, we always use the lower safety rating from the version without the additional safety equipment. 

Which? safety assessments

We also conduct our safety assessments, including how well the car protects its occupants and pedestrians in an accident, how easy it is to fit a variety of child car seats, and the safety of factory-fitted and optional equipment.

We also assess cars based on other safety features. This includes the 'pinch' test, which measures the force it takes to stop a car window from closing and whether it poses a risk to fingers.

Efficiency

Many cars struggle to meet their official fuel economy (mpg) figures when they’re faced with our tougher (but more realistic) tests, which include a motorway element to truly assess fuel consumption at high speeds.

We also measure emissions in the same stringent tests and have found a large number of cars that, although they pass official tests, emit large quantities of toxic gases such as NOx and CO. 

Petrol, diesel and mild-hybrid efficiency

We carry out our fuel-economy test on a rolling road in a lab. This simulates wind resistance and lets us repeat the test in the same way in the exact same environment, as we use the same lab for each car test.

We use the Worldwide Harmonised Light Vehicles Test Cycle (WLTC) and run both a ‘cold cycle’ (where the engine is cold) and a ‘hot cycle’ (where the engine is already warm).

There's also a motorway driving cycle, where we accelerate up to – and sustain – motorway speeds. 

We set the conditions of the test to be as realistic as possible:

• We test cars in the default setting they start up in, rather than switching to a more economical driving mode.
• Our additional test cycles are conducted with the air conditioning on, lights on dipped beam (or daytime running lights) and the radio switched on.
• We don’t tamper with the cars by removing extra weight or inflating the tyres any more than specified in the owner’s manual.

Full hybrid efficiency

When testing the efficiency of full hybrids, we conduct our test with a 60-70% state of charge displayed on the on-board computer.

Plug-in hybrid efficiency

For plug-in hybrids, we start our motorway and warm cycles with an empty battery. We then run our cold cycle immediately afterwards, with whatever battery charge the car has after completing the warm cycle.

We also run a custom cycle with a fully charged battery, which we repeat until the engine turns on. After this cycle, we charge the car to work out how much electricity has been used.

The ratio between pure electric and engine-only driving for each car determines how much we factor each type of driving into our consumption figures.

Electric car efficiency

When testing EVs, we combine the WLTC cycle and our own motorway cycle.

Through repeat tests, we can work out a realistic range that an electric car can travel.

Emissions

While testing a car's efficiency, we also collect air-polluting emissions data. This is the quantity of exhaust emissions – such as oxides of nitrogen (NOx), carbon monoxide (CO), hydrocarbons (HC) and particulate matter (PM).

Any vehicle that produces a very large amount of air pollution in our tests can't be a Best Buy.

How we rate car emissions

Comfort and practicality

Our comfort and practicality tests include how easy it is to get in and out of the car, and the maximum height of occupants. We also measure road, wind and engine noise and assess how well the car deals with bumps, from large potholes to jittery surfaces like cobblestones.

Entry and exit

We assess every car on how effortless it is to get in and out. This is particularly important if you or any of your regular passengers have mobility issues or are particularly tall.

Seat comfort

We also look at how well padded and supportive the seats are, making expert assessments of lumbar, thigh and head support.

Ride quality

How comfortable you’ll be depends on how well the car handles the lumps, bumps and gaping potholes that are common on UK roads. Our test track has all those features and more.

Quietness

A noisy car can make long journeys a chore. We measure and subjectively assess road, wind and engine noise in each car we test.

Seat space

We use a life-sized dummy to work out precisely how much head, leg and knee space there is for the driver and all passengers.

Boot space

Car manufacturers vary in how they measure their claimed boot space, which can include removing carpets or counting spaces that would normally be filled with a spare wheel. 

We load the boot with foam blocks to figure out the usable amount of space, ignoring useless nooks and crannies.

Ease of driving

To find out how easy a car is to drive, we assess everything from visibility and handling to the cabin layout and how smoothly the engine delivers its power.

Visibility

Regardless of how many parking aids you've got fitted, a car with large blind spots will feel cumbersome to drive.

Below is the rear section of a 360-degree interior image of the Mercedes-Benz GLC Coupé (2016-2022). Obstructions to the driver’s all-round field of vision are colour-coded depending on what the obstruction is and how severely it interrupts the driver’s vision.

Dark blue: Anything that disturbs the view directly below the mid-point line.

Pink: Anything above the middle line directly to the rear and therefore considered more detrimental to visibility.

Light blue: This measures narrow windows. These are positive rather than negative, and improve the ratings for the adjacent pillars (coloured in yellow and pink).

Smoothness of power delivery

If a car delivers power smoothly, we’ll reward it with a high score. But if the power is delivered unevenly, the car’s engine vibrates a lot and the engine is very noisy when accelerating, then the car’s power delivery score will be poor.

Driving stability

We put all cars through the Which? hazard-avoidance test. If you find yourself in a situation where you have to swerve around something – or someone – at the last moment, you need to be sure your car will remain controllable.

Travelling at speeds of up to 56mph, we conduct a test in which we swerve around an object and rejoin the original lane. This determines how stable and controllable a car remains, and whether it's likely to understeer (lose grip from the front and continue in a straight line) or oversteer (where the rear axle loses traction, potentially resulting in a spin).

The assessment factors in the behaviour of a car's electronic stability control system and how likely it is to keep the car on its intended line, should you need to make a sudden manoeuvre.

Cabin layout

Our lab tests comprehensively assess how intuitive the car’s cabin controls are. We reward cars with logically designed cabins, and we assess how easy it would be for someone to get used to the car’s interior controls. We also check for poor interior ergonomics and reduce the test score in this category accordingly.

Driving performance

Brakes

We conduct repeated emergency stop tests from 62mph (100km/h) and record the average distance covered over 10 attempts. Not only does this allow us to assess a car’s overall braking performance, but it also shows whether that performance is consistent and how likely it is that the brakes will overheat or fade. We score braking distances on a sliding scale, with 30 metres representing a perfect score, and 43 metres the very worst.

Acceleration

We test acceleration to recreate real-world scenarios where speeding up quickly is important. This includes overtaking at motorway speeds and merging into fast-flowing traffic. 

Gearbox and transmission

For manual cars, we rate how easy the gear lever is to use and how seamless gear changes are. For automatics, we evaluate how seamless the automatic gear shifts are and if they occur at the appropriate time.

For electric cars, we rate how easy the gear lever is to operate; this is particularly important when making multi-point turns while parking.

What separates a good result from a poor one?

We rate a car’s overall build quality between one and five stars. A five-star car will have luxurious cabin materials and will be built to very high standards, while a three-star car may have poorly aligned body panels, lots of scratchy plastic in the cabin and basic carpet and roof-lining materials.

How we calculate the scores

Neal Rimmer, Which? senior scientific advisor, says: ‘Along with detailed reliability information, each car review includes ratings on a number of lab and road tests, allowing us to assess how it performs against its peers.

‘We thoroughly assess our testing processes and evaluations every year to ensure they stay up to date and useful to you. We also ask the Which? community what matters most when choosing a new car.’

How we pick Eco Buy cars

Eco Buy cars produce the least amount of greenhouse gas emissions when in use.

We calculate a CO2 (or equivalent) figure per kilometre driven, which allows us to compare emissions across all fuel types. This includes the transmission of electricity from a UK power station (based on the UK's renewable/non-renewable electricity mix) to an electric car's battery, or the extraction, transportation and distribution of petrol or diesel to the point at which it enters the car's fuel tank. 

For cars that use petrol or diesel, the figure also includes CO2 emissions from the tailpipe in our tests.

All Eco Buy cars must also get at least four stars in our electricity efficiency tests.

In addition to emissions criteria, Eco Buys must also score at least 66% in our lab tests and have a reliability rating of at least three out of five stars (when they have a rating) in our annual Which? car survey.

How we pick Great Value cars

While they might not be Best Buys, Great Value cars still score highly in our tests while also being significantly cheaper to buy than the average car in their class. 

Using six months of our unique pricing data, we look at the average lowest price for each car we test. This is the price of the lowest trim level available, accounting for typical dealer discounts or manufacturer contributions. 

Great Value cars must score at least 65%. In addition, if tested by Euro NCAP they must get at least three stars and, if we have data on the car, a reliability score of at least three stars. 

We update our list of Great Value cars every six months.

Our car experts

Running our test projects is a group effort, with several experts from across the team contributing to each one.

Here's the team that makes it happen:

Senior researcher & writer, Dino Buratti: Dino dissects lab reports and turns them into jargon-free, in-depth reviews and advice to give you the best possible information you need to choose a new car.

Senior researcher & writer, Michael Passingham: Alongside Dino, Michael oversees our car lab testing, writes reviews and also specialises in road safety issues. Michael is a member of the Euro NCAP communications working group, ensuring that the latest car safety developments are clearly relayed to car buyers.

Senior scientific advisor, Neal Rimmer: Neal analyses and evaluates our reliability, safety, laboratory and performance data, converting it into our clear test scores and star ratings. He also ensures our results are rigorously accurate and our evaluation methods stay up to date to meet our members' needs.

Cars editor, Will Stapley: Will ensures our content is both useful and relevant to UK drivers, keeping a close eye on accuracy and fairness. He also pays close attention to your feedback, ensuring we’re covering the areas you want us to.

All car testing images: Which?/Abgedreht