Roller brake testers, as used in  a vehicle workshop / MOT test to test the efficiency of a vehicles braking ability, which is known as brake efficiency and normally displayed as a percentage % value. Depending on the age and type of brake system fitted to your vehicle different pass / fail efficiency’s exist, refer to MOT inspection manual: cars and passenger vehicles – 1. Brakes – Guidance – GOV.UK (www.gov.uk) to understand which efficiency value the vehicle should be tested against.    

Starting back at basics, by default roller brake tester operates by turning the vehicle wheels (using a motor within the roller brake tester) so the person testing the vehicle can then apply the vehicle brakes (from within the vehicle) against the force of the motor to evaluate the brake performance of the vehicle, the Roller brake tester contains a measuring transducer which allows the force the vehicle is producing to be displayed on either a gauge or display which when this force is used in conjunction with the vehicle weight  the percentage efficiency can be calculated. 

This process works really well to test and measure service brakes (foot brakes) but is not so good when conducting a parking brake test. Parking brakes are by design used to ensure a vehicle does not roll away when parked up (wheels not rotating)  so applying the parking brake whilst the wheels are turning is not a true test of the brake force the parking brake is able to produce, with the introduction of electronic parking brake systems this has been escalated as electronic parking brakes are either on or off, so when tested on the roller brake tester, they have a tendency to be applied too quickly and thus eject the vehicle under test out of the testing rollers, which can result in incorrect efficiency reading being recorded for the parking brake system, and can also be a hazard to anybody stood near the vehicle when it gets ejected from the roller. 

So an applied Brake test was developed, in an applied parking brake test, the vehicle is positioned on the rollers and the parking brake is applied, now the Roller brake tester will, using special software and motor control circuits apply progressively more torque to the rollers to try and turn the vehicle wheels, as such a true brake efficiency reading can be obtained from the parking brake system and the hazard of the vehicle being ejected from the rollers is removed.

A further advantage of using an applied parking brake test is this can also be used not only with electronic parking brakes but can be used on traditional parking brake systems, and on all 4×4 vehicle’s or vehicles with special drive differentials as the wheels on the vehicle are not turning whilst the test is being conducted.

Note:

1. Applied brake testing  must only be done on a Roller brake tester fitted with the special software and motor controls, otherwise you will end up just damaging the vehicle tyre and also potently the roller brake tester its self. 
2. Only Roller brake testers which have been tested and verified as meeting the DVSA requirements will be issued a new equipment identification number (EIN) ending with suffix “APB” 

If you unsure if your RBT can conduct an applied parking brake test or be upgraded to do so then contact your equipment supplier / maintainer for further information.