Heavy vehicle brake test: best practice

Published 13 April 2016

Applies to England, Scotland and Wales

1. Introduction

We aim to carry out an effective check of the performance of your vehicle and trailer brakes – with as little inconvenience to you as possible. This guide gives you some clear and effective advice on how to achieve a satisfactory result from the brake-testing element of the MOT.

Roller brake test

1.1 Locked wheels and the brake test

Vehicles must be fully loaded before being roller-brake tested because the grip between the tyre and the rollers is more effective that way. The wheels keep turning for longer, and a higher brake force will be achieved.

If your vehicle is empty or only lightly loaded, the grip between tyre and the road (or the rollers on a roller- brake tester or ’RBT’) will be lower, and a relatively small brake force will cause the wheels to lock (stop turning).

Once locked, no matter how much more the brakes are applied, the recorded brake force won’t increase. This means that if the vehicle’s load is too light, the wheels may lock before achieving the required brake efficiency.

If a vehicle is properly loaded, there are two concessions in the HGV inspection manual that Driver and Vehicle Standards Agency (DVSA) inspectors can make:

  • front wheel lock allowance (FWA): this takes into account the weight transfer to the front axle(s) that occurs when the vehicle is on the road

  • passing on locks (locked wheels): if more than half the wheels on a system lock, then the vehicle will pass on locks, unless there’s another reason for failure

You shouldn’t rely on either condition during test preparations. If the wheels don’t lock in the actual test, the vehicle will have to meet the required efficiency.

Remember: a locked wheel does not always mean a good brake.

2. Preparing your vehicle for the brake test

Authorised Test Facilities (ATFs) are responsible for making sure that vehicles are properly loaded before the MOT starts. This normally means at least 65% of the vehicle design axle weight (DAW).

You can do this in a number of ways:

  • by arranging to load the vehicle or trailer yourself

  • by asking the ATF to provide load simulation - a loading fee may apply

  • in the case of a tractor unit, using ballasted trailers - ask your local ATF if they have one for hire

Where load simulators can’t be placed above the rear axles, vehicles or trailers - unless exempt by design - must be loaded when tested. This includes:

  • any multi-axle vehicle or trailer (excluding tri-axle semi-trailers) with a bogie weight exceeding 10,000kg

  • tri-axle tractor units that are fitted with air suspension on any of the rear axles: to provide sufficient load these must be coupled to a loaded semi-trailer, so that the drive axle is loaded at or very close to the plated weight shown in column 2 of the plate and plating certificate

When loading a vehicle for brake test:

  • place loads close to the rear axles
  • aim to apply at least 65% - and not less than 50% - of the design axle weight to each axle
  • if possible, use similar loads to add weight to the vehicle: this will help in placing the loads correctly, and achieve consistency between tests
  • where load simulators can’t be placed above the axles - unless exempted by design - the vehicle or trailer must be presented laden

Note: our examiners can refuse to conduct a brake test if they’re unable to carry out a satisfactory one.

2.1 Conditions for testing when unladen

The following table isn’t meant to be extensive, but outlines the circumstance under which we may allow an unladen test, and gives examples of vehicles that we think fit the criteria.

The belief is that these vehicles aren’t able to be presented in the laden condition due to basic design limitations, or restrictions caused by the type of cargo they normally carry.

Our recommendation is always: if you can load it, then do so!

Vehicles designed for and normally carrying Examples
Obnoxious loads Food/animal/human waste
Livestock Horses, sheep, cattle etc
Fixed plant White lining vehicle, road sweeper, access platforms etc
Perishable liquids/goods vulnerable to contamination Liquid/powder tankers, concrete mixers
With small or restricted loading/access through openings Catering vans, mobile libraries, bullion vehicles, pigeon transporter, compactor vehicles (bin lorries)
With low load-bearing ability or false floors Furniture removal vehicles
Which are near to 65% DAW when unladen (not less than 50%) Compactor vehicles (bin lorries), road sweeper

Dangerous and hazardous goods vehicles and trailers must be presented in line with the advice given in the Guide to the inspection of dangerous and hazardous goods vehicles.

Remember: only in exceptional circumstances will we check the performance of the brakes when the vehicle is unladen.

3. If you have a brake tester

3.1 Condition

  • make sure that rollers are clean, in good condition and well gritted
  • your brake tester should be serviced and must be calibrated in line with manufacturers’ instructions

3.2 Procedure

Present your vehicle loaded to at least 65% of design axle weight - unless exempt - and follow the DVSA brake test procedure. More guidance is available in the HGV inspection manual.

3.3 For computer controlled RBTs

Make sure you have a current version of DVSA’s DTp (now DfT) number database installed in your machine so that new vehicles are recognised. This will also remove the need to manually input vehicle details (which could result in the wrong FWA being used).

3.4 For manual RBTs

You’ll need to decide what the vehicle’s braking needs are. These will help calculate brake performance.

3.5 For decelerometer

Only a limited number of ATFs are able to conduct decelerometer testing, and generally only if:

  • the vehicle is the kind which a roller-brake test can’t be carried out on
  • it’s not possible to carry out a roller-brake test
  • the roller-brake tester isn’t working

If your vehicle needs this type of test, please contact your ATF before booking to make sure they can do it.

4. If you don’t have a brake tester

4.1 Regular brake performance checks

You should check brake performance regularly as part of a vehicle’s maintenance. It’s also a good idea to test brakes as part of the vehicle’s preparation for annual test.

4.2 Where to get your brakes tested

You can ask:

  • franchised dealers
  • vehicle repairers
  • local authorities

5. General advice

5.1 Aim high

Maintain vehicles regularly, so that they meet the minimum standards when used on a road.

Remember: a locked wheel doesn’t always mean a good brake! It’s important for all wheels to be able to meet the required standard.

5.2 Load the vehicle

Unless exempt, the vehicle must be loaded whenever the vehicle is brake tested. It gives higher brake forces before wheel lock, which reflects the performance of the vehicle when in use.

5.3 Steam cleaning

Use common sense, steam-cleaning the vehicle brake system immediately before test is highly likely to reduce the brake performance.

5.4 Load-sensing valve (LSV)

It shouldn’t be necessary to alter the load-sensing valve settings outside of the manufacturer’s pre-set limit to achieve a satisfactory brake result. Altering the LSV settings can lead to over-braking of the rear wheels which is a potential road safety hazard.

5.5 Secondary braking systems

Vehicles are fitted with a secondary brake, typically either through a split braking system, or a progressively applied hand control valve. Make sure you know which type your vehicle has, and if the other system can be used as an alternative.

5.6 Pre MOT RBT Checklist:

  • is the vehicle sufficiently loaded?
  • have all the brakes had time to bed in?
  • are you aware of the correct method of inspection?
  • is the RBT calibrated and in good condition?
  • has the vehicle exceeded the minimum efficiency required in the manual?