How we test cars How we test brakes
The Which? Car braking test highlights any problems with a car's braking system, whether it be an excessively long stopping distance or a drop-off in performance after repeated applications (brake fade).
Car owners often take the middle pedal in their car for granted – until an emergency. Every car tested in the Which? Car test centre gets an exhaustive (and exhausting) brake test to determine how they compare for stopping ability.
It's important that the Which? Car brake test eliminates unwanted variables, so we test on the same (dry) surface each time, and make sure there's no ice or dust to influence the result.
Volkswagen's latest Polo in testing. Note how far front wheels are forced rearwards under heavy braking
To ensure a realistic result, before each test we set up the car at half load (with two adult passengers) and ensure tyre pressures are correct.
We then perform an emergency stop test from 62mph to 0mph and measure the stopping distance using a GPS-based Racelogic tracking computer – the same kit used by racing teams. More importantly, we repeat this emergency stop test another nine times in quick succession.
The average of these 10 braking tests is the overall braking distance figure we quote for each car. This gives the brakes a real pounding, and the test is designed to highlight any tendency to fade – that is, where brake performance reduces as brake temperature increases.
This Peugeot 206 SW (estate) braking hard from 62mph to a dead stop
Any car that exhibits fade is marked down accordingly. Fortunately, it’s less common on modern cars, most of which have strong, predictable braking performance.
A lot of other factors influence braking performance: the brakes themselves and their ability to dissipate heat, and electronic controls, such as anti-lock brake devices. Tyres are also critical – in the past we noticed that ‘eco-tuned’ cars with tyres optimised for economy tended to have longer stopping distances than their regular counterparts. However, carmakers seem to be addressing this, as the latest eco cars we've tested have better braking power.
We also monitor the brake pedal in normal use, as the pedal weighting is critical to give the driver and passenger a smooth ride. Some cars are over-assisted, meaning a very light touch on the pedal results in a lurchy, uncomfortable stop – cars showing this trait are also marked down. We haven’t come across any cars with a pedal that is too heavy, though – thankfully un-assisted brakes are a thing of the past.