How we test cars Lab test

Testing cars in our lab is crucial to ensuring we have measurable tests carried out in a controlled environment that can be used to compare models directly.

Lab test – controlled, measurable and comparable tests

Test lab

Our controlled lab tests mean we can directly compare cars

After we’ve had hands-on experience with every key car for the UK market, we send each car to our test lab – the biggest car-testing facility in Europe. It’s here that we carry out measured tests of each new model, making it easy for you to directly compare one vehicle against another.

The ratings for each of these tests is used to calculate our total test score – the overall rating we give each car before we factor in any survey results. Ours are the only UK tests done independently, with no influence from advertising or manufacturers.

We test the things you really want to know about a new car - things the claims on manufacturer specification sheets can't tell you. That’s where we come in – our tests are not only measured but also conducted with real-life experience in mind, giving you a clearer idea of what to expect from a car.

You can find out the results of these tests in all our car reviews.

So what exactly do we test? Here’s a rundown of some of the more important measured lab tests we undertake.

Which? Car eco test

We carry out the eco test on a rolling road

Environment and eco test

We simulate the real conditions of driving on our rolling road. We have large industrial fans that replicate the wind resistance dependent on the driving cycle to ensure we have the most realistic readings.

Exhaust emissions and fuel consumption tests are conducted within the measures of the New European Driving Cycle (NDEC). However, our test includes urban and extra-urban cycles under cold-start conditions (replicating getting into your car and driving away immediately as you might first thing in the morning) and a second test with the engine warmed up and the air conditioning on. We also conduct a motorway driving cycle at a top speed of 81mph (the maximum limit in most European countries) with full throttle acceleration periods (replicating speeding up when merging onto motorways). If you want to know more, read about How we test mpg.

Use our fuel economy calculator to work out how fuel efficient your car is.

All-round visibility measurements

Rather than subjectively saying visibility is good or bad, we take measurements from all round the car using a moving camera, and measure the size of the mirrors and the view in front and behind the vehicle through the windows to find out where there are restrictions.

Which? Car heating test

Our heating test is conducted in a temperature-regulated chamber

Heating test

Using our special climate chamber, we measure the time required to heat up the cabin from -10°C to +22°C front and rear at five height levels using dummies with temperature sensors fitted to them in the vehicle. In preparation, we leave the car in -10°C in the chamber for at least six hours to ensure the starting temperature is correct. We then drive the car on a rolling road in the chamber at a constant speed of 40kph with measurements of temperature on the dummy positions taken every 10 seconds.

Interior space measurements

We don’t just get inside the car and comment on the amount of room inside – we have a cabin dummy that we use to take measurements of space in both front seats and the back seats of every vehicle. We even adjust the front seats to accommodate the most common-sized male driver/passenger of 1.85m tall.

Which? Car interior noise test

We measure interior noise with a dB meter

Interior noise measurements

To make sure we have the most realistic measurement of interior noise, we use a sound level meter to measure the dB level inside the cabin centre when travelling at 81mph with a half load and standard summer tyres. We take the measurement on the motorway in both direction to calculate the average figure.

Engine performance measurement

It’s all well and good to know the 0-62mph speed of a car, but in the real world it’s the overtaking time you really need to know about. That’s why we calculate this by measuring the time taken to accelerate from 37mph to 62mph. This test is carried out under half load (two adults on-board) with summer tyres, and is electronically measured using GPS. We don’t change gear either, to replicate the way the most people overtake – we measure the overtaking time in fourth, fifth and, where necessary, sixth gear, without shifting up.

Which? Car avoidance test

We carry out an avoidance test at our facility

Avoidance test

You won’t know how good the stability of a car is until you really need it - when you have to take emergency evasive action. That’s why we conduct an avoidance test, swerving around cones placed in the exact same position every time at our testing facility. We conduct the test travelling at speeds up to 56mph and we make judgements on the reaction to sudden steering. The assessment also includes ESC intervention to stabilise the car, understeer and skidding, tightening steering and the risk of overturning.

See footage of the Citroën Nemo MPV rolling over in our avoidance test.

Brake test

We also measure braking distances, braking to a standstill from 62mph at half load with summer tyres fitted. An electronic GPS measurement system is used to give the most accurate reading. We do this 10 times and use the average reading, taking into account possible brake fade.

More on this...

  • Which? Car Survey - how your input affects our overall test scores
  • Road test - details of our hands on test with each car
  • Car reviews - the results of our findings in hundreds of car reviews