Understanding your PSV/HGV Roller Brake Test report

As a transport manager for a PSV or HGV operation, ensuring the safety and roadworthiness of your fleet is paramount. Brake performance is one of the most critical safety aspects, and understanding brake test reports is essential for effective maintenance and compliance. This guide equips you with the knowledge to interpret Roller Brake Test (RBT) reports and understand their significance — complementing our wider RBT report breakdown.

What is a Roller Brake Test?

A Roller Brake Test is a sophisticated method used to assess a vehicle's braking performance, measuring braking force per wheel while the vehicle is stationary on rotating rollers. The process is straightforward: each axle is positioned on the rollers, the wheels are spun at a controlled speed, the service, secondary and parking brakes are applied gradually, and sensors measure the braking force (typically in kilogram-force, kgf) generated by each wheel.

RBT versus decelerometer brake test

A decelerometer measures overall deceleration (g-force) on a moving vehicle and gives only overall braking efficiency — it can mask individual brake faults. The RBT measures braking force per wheel in controlled conditions, exposing uneven braking, binding or a single weak brake.

From April 2025, RBT or EBPMS (Electronic Brake Performance Monitoring System) will be the primary accepted methods, with the decelerometer acceptable as an alternative where RBT is not possible.

Reading the report: brake performance by axle

The core of the report details each brake on each axle, typically showing nearside (N/S) and offside (O/S) figures. The key terms are:

• Max Force (kgf) — the maximum braking force per wheel. If it is less than 5% of the measured axle weight for a wheel, that indicates a significant issue and will likely fail.
• Imbalance (%) — the percentage difference in force between the two wheels on an axle. For service and designated secondary brakes, more than 30% fails; even a 20–29% imbalance warrants investigation.
• Bind (%) — residual braking force when brakes are released. More than 4% bind on service brakes fails, and any binding wastes fuel and accelerates wear.
• Time Lag — how simultaneously the brakes on an axle apply and release; often a manual assessment by the tester.
• Ovality (%) — variation in force during one wheel rotation, indicating a warped or out-of-round drum or disc; 70% or higher typically fails.
• Lock-up — often shown as "(L)". A pass can be recorded even if a wheel locks (especially unladen), which is exactly why laden testing matters.

Test summary and efficiencies

The summary reports the minimum braking efficiency required for each system against what was achieved — the headline pass/fail figure, calculated as total braking force of all wheels divided by total measured vehicle weight, times 100.

Interpreting the report and taking action

Simply seeing "PASS" is not enough — you need to dig deeper. Ask whether efficiencies are comfortably above the minimum (being just above could hint at underlying issues), whether any imbalances suggest a specific brake problem, whether there is any binding, and whether forces are consistent across and between axles. Confirm the test was laden (ideally ≥65% of axle design weight) or that there is a documented risk assessment for an unladen test. Compare current reports with previous ones and with sister vehicles to spot declining trends early.

Then act: file the report as a vital legal document, investigate "near misses" and advisories — not just failures, schedule and document any repairs to build an audit trail, re-test after significant brake work, use the report as a diagnostic tool with your technicians, and review your preventative maintenance procedures if recurrent issues appear across the fleet. A defensible compliance record across maintenance and drivers' hours is your best protection at a Public Inquiry.

Train your team to read brake tests

Understanding the RBT report is an indispensable skill for any transport manager. For structured, hands-on learning, our two-hour virtual RBT training and our RBT Risk Assessment Generator help you turn data into action. Contact us to discuss training for your team or for support interpreting a specific report.