Brake Efficiency Classes 3,4 & 7

1.  Brake Efficiency (Classes 3, 4 & 7)
The brake efficiency will be calculated by the VTS Device using the following methods (having taken into account wheel lock where appropriate). Total up the braking effort recorded from all the wheels of the vehicle when the service brake is applied. Total up the braking effort recorded from the appropriate wheels when the parking brake is applied. Calculate the service brake and parking brake percentage efficiencies by following the procedures detailed below according to the Class of vehicle tested.

Class 3 & 4

Determine the brake testing weight for the vehicle, e.g. from the VTS Device. The weight includes an element of 140kg for the driver, fuel, tools, etc.

Calculate the service brake percentage efficiency by dividing the total brake effort achieved when the service brake is applied by the vehicle weight and then multiplying the result by 100 

Total Brake Effort / Vehicle Weight X 100 = % Efficiency

Calculate the parking brake percentage efficiency by dividing the total brake effort achieved when the parking brake is applied by the vehicle weight and then multiplying the result by 100, as above.

Class 7 Vehicles

Obtain the vehicle Design Gross Weight (DGW) from the manufacturer’s plate fitted to the vehicle (see Section 3.9) or from the VTS Device.   If a ‘Department for Transport plate’ (commonly called ‘Ministry’ plate) is fitted to the vehicle the DGW should be obtained from here.

Calculate the service brake percentage efficiency by dividing the total brake effort achieved when the service brake is applied by the vehicle DGW and then multiplying the result by 100.

Total Brake Effort / DGW X 100 = % Efficiency

Calculate the parking brake percentage efficiency by dividing the total brake effort achieved when the parking brake is applied by the vehicle DGW and then multiplying the result by 100, as above.

Note:  Plate Brake Test Only Vehicles with a presented weight of 2000kg or more must be tested to the above criteria.  On vehicles with a presented weight of less than 2000kg, the brake efficiency must be calculated using a nominal DGW figure of 2600kg.

Total Brake Effort / 2600 X 100 = % Efficiency                    

Alternatively, if ATL approved the computer controlled brake tester will automatically calculate the efficiency and any out of balance.

Brake out of Balance

The out of balance of the braking effort on the front steered wheels when the service brake is applied is obtained by compairing the brake efforts at each front wheel when they are tested simultaneously (see sub section 3.7.2) Carry out the following calculation to determine the percentage imbalance:

                                (Higher brake effort - Lower brake effort) x 100 = % imbalance
Higher brake effort

Brake Efficiency ( Class 5)

2. Brake Efficiency (Class 5)

The brake efficiency will be calculated by the VTS Device using the following methods (having taken into account wheel lock where appropriate).

Total up the braking effort recorded from all the wheels of the vehicle when the service brake is applied. Total up the braking effort recorded from the appropriate wheels when the parking brake is applied.

The service brake and parking brake percentage efficiencies may be calculated by using the procedures detailed below

Service Brake Efficiency
Calculate the service brake percentage efficiency by dividing the total brake effort achieved when the service brake is applied by the vehicle design gross weight (DGW) and then multiplying the result by 100.

Total Service Brake Effort / DGW X 100 = % Efficiency

Parking Brake Efficiency
Calculate the parking brake percentage efficiency by dividing the total brake effort achieved when the parking brake is applied by the vehicle design  gross weight (DGW) and then multiplying by 100.

Total Parking Brake Effort / DGW X 100 = % Efficiency

The DGW is normally shown on the manufacturers’ plate.  Where only the unladen weight   is shown on the vehicle, calculate the DGW as follows

[Number of passenger seats (excluding the driver’s seat) X 63.5kg (or 140lbs)] + unladen weight

3. Brake out of Balance
The out of balance of the braking effort on the front steered wheels when the service brake is applied is obtained by compairing the brake efforts at each front wheel when they are tested simultaneously (see sub section 3.7.2) Carry out the following calculation to determine the percentage imbalance:

                                (Higher brake effort - Lower brake effort) x 100 = % imbalance
Higher brake effort

Issue Date 01 January 2012