A Locked Wheel Does Not Always Mean A Good Brake



According to DVSA Heavy vehicle brake test -best practice, all 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 tyres 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: 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.

In April 2016 the DVSA published ‘Guide to Electronic Brake Performance Monitoring System(s)‘ which enables (EBPMS) to used as evidence for the operators’ preventative maintenance system, Over the last 3 years we have developed our patented Electronic Brake Performance Monitoring System (EBPMS), which could help you avoid the need and expense to carry out a laden roller brake test  (a test considered by many to be flawed).