Everything you need to know about Roller Brake Tests

In February 2022, the DVSA released guidance around “Understanding your HGV or trailer’s brake test report”, confirming that you 'should' get your HGV or trailer’s brakes tested by a roller brake test (RBT) at least four times per year, including once at MOT. With tons of operator’s now being penalised for failing to do this, hopefully, with the new release of the GTMR out soon, clarity will be given on how brake testing ‘must' be done and once again, one of the many grey areas of vehicle maintenance can be clarified with a definitive answer.

For a brake test to be meaningful and count towards one of your four annual RBT’s, your vehicle or trailer must be tested laden – ideally to at least 65% of its total maximum weight (no less than 5o%).?If your vehicle is insufficiently loaded, essentially your brake test is about much use as a chocolate fire guard, unless of course, your vehicle or trailer is exempt… but we will get to that later!

Roller Brake Testing is vastly misunderstood by hundreds of operators and maintenance providers across the UK, and no wonder, as the documentation can be particularly misleading. So how do we get over this hurdle? We learn how to read and understand our brake test reports, which is what I’m hoping to help you with.

How to read a RBT

Your brake test report will overall tell you whether you passed or failed. There are 3 sections, which include:

·???????Details of the vehicle being tested

·???????Information about the brake performance of each axle

·???????A summary of the test results for each brake system (brake efficiencies)

Section 1: Information about your Vehicle

Fairly self-explanatory. This section has the details of the vehicle or trailer undergoing the test including:

-???????Vehicle Registration Details

-???????Make & Model

-???????Maximum Design Weights – Depending on the type of vehicle or trailer, the design weight will be displayed as either:

• GVW – Fully loaded vehicle or trailer
• GTW – Fully loaded vehicle and trailer
• TAW – Fully loaded trailer axles.

-???????Test Centre/Date & Time of Test

-???????DTp Number (Important to check! This tells the computer the exact spec of the brake test, so if these are entered incorrectly, then the test result could be wrong. The number should match with the plating certificate)

(Example of Section 1)

Section 2: Brake Performance by Axle

This section looks at each axle and shows the axle weight at the time of testing. The report then continues to show the braking system on each side of each axle, checking the bind, time lag, ovality, imbalance and max force as well as indicating if the brakes locked.

Bind – The bind reading checks to see if the brakes bind when the brake is not applied. It is only displayed against the service brake performance.

Time Lag – This is a check to ensure that each of the brakes on the same axle apply and release at the same time as each other. It’s not measured by the roller test computer, so will always be shown as a pass on your report.

Ovality – Ovality measures if there is any difference in the braking effort as each wheel rotates and it’s only checked on HGV’s steered axles. The vehicle will fail if there is a difference of more than 70% between the highest and lowest brake reading at a steady pedal pressure. The result will be shown as either a ‘Pass’ or ‘Fail’. If it’s a failure, the reading will be shown as a percentage under the ‘Unsatisfactory wheel performance’ heading. ?

Imbalance – This is a check for the percentage variation between the brakes on the same axle. The report shows the braking force of each brake on one axle and the variation percentage between the nearside and the offside. The vehicle will fail if the brake imbalance is more than 30%. However, this does not apply if both wheels lock, or if one-wheel locks and the braking effort of the locked wheel is less than that of the other, so it is really important to look at imbalances and if it is 30% + investigate this and get those brakes adjusted.

Max Force - This is the maximum braking effort or braking force for each brake shown in kg. It is worth watching out for the (L) after the force figure which would indicate the brake locked and therefore the potential braking effort could have been higher.

(Example of Section 2)

As you can see above, the report will show the weight of each axle in kg. It must be at least 50% of the design axle weight displayed on the manufacturers plate and plating certificate. You should aim for each axle to weigh at least 65% of the design axle weight. If any axle weighs less than 65%, an ‘insufficient load’ message will be included in the test summary. This does not include vehicle front axles.

The main two things to look for in section 2 is a significant imbalance in the brakes (this is a clear indication that maintenance is required on the brakes) and that the vehicle/trailer is sufficiently loaded.

If your vehicle fails any of these checks, the result will be shown under the ‘Unsatisfactory Wheel Performance’ header at the bottom of the brake test report.

When it will fail

• Bind (service brake only) - More than 4%
• Time lag - Manual assessment made
• Ovality - 70% or higher
• Imbalance (service and designated secondary brake only) - More than 30%
• Max force - Less than 5%

Section 3: The Test Summary

The final section summarises how the vehicle or trailer has performed during the roller brake test. This section identifies the total measured vehicle weight (all axle weights added together), highlight if any axle had insufficient load, identify the values required by each braking system to pass the test (pass value), show the achieved test value during the test for each braking system, and finally the overall result of the roller brake test.

(Example of Section 3)

If your test value says ‘FWA’

If any of your test value results have front wheel lock allowance ‘(FWA)’ after it, one or more of your front wheels locked during the test. For trailers, front wheel lock allowance (FWA) only applies to one or two front steered axles on full drawbar trailers.

If a result says ‘Pass (Locks)’

If your report shows a result of ‘Pass (Locks)’, your vehicle will have passed because more than half of its wheels locked during the test. Although your vehicle passed, your wheels may have locked too quickly to give accurate results. If this was because your vehicle wasn’t loaded to at least 65% of its weight, you should get another brake test with a properly-loaded vehicle as soon as you can.

So, an example of a Good Laden RBT would be the following:

But why?

·???????The vehicle was loaded at 76% of it’s capacity therefore being a meaningful laden RBT as it was sufficiently loaded as it exceeds the 50 – 65% requirement.

·???????All the imbalances are reasonable with the highest being 14%. If your vehicle passes the imbalance check but the imbalance is over 25% you should investigate why this is and look to adjust your brakes to lower the imbalance. Imbalanced brakes can cause the vehicle to pull to one side under heavy braking.

·???????All test values are equal to or above the required pass value set by DVSA.

To calculate Brake Performance:

1.??????Add up all of the brake force figures for the service brake on each axle to give you your total break force,

2.??????Divide the total brake force by the weight as specified in the pass value column.

3.??????Multiply by 100 to get the %, rounding up or down to the nearest number

Brake Performance % - Brake Effort x 100

??????????????????????????????????? Weight

Exemptions

The following list isn’t isn't set in stone but does give a brief outline on the circumstance under which unladen tests may be accepted and gives examples of vehicles that are believed to fall in the 'exempt' category. This is due to the fact that things such as design restrictions or limitations caused by the type of cargo they normally carry.

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

or

• 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.

Tri-Axle Semi Trailers

Due to the difficulty of loading a tri-axle semi-trailer for a brake test, it is accepted that these can be tested unladen, however, to pass their test, the service and parking brake systems must achieve a specified level of brake force depending on the number of wheels that lock.

Service Brake Performance Requirements

Below shows the minimum total brake force that the service brake must achieve depending on the number of wheels that lock during the test. (Add up all the service brake wheels to find out your brake force)

Number of Wheels Locking & Minimum Total Brake Force Required

6 Wheels - 3000 kg

5 Wheels - 3600 kg

4 Wheels - 4200 kg

3 or Fewer Wheels - Normal Laden Trailer Requirements. Apply??????????????????????????????????????????

Parking Brake Performance Requirements

Below shows the minimum total brake force that the parking brake must achieve depending on the number of wheels that lock during the test. (Add up all the parking brake wheels to find out your brake force)

Number of Wheels Locking & Minimum Total Brake Force Required

• All wheels on which the parking brake operates lock - 1500 kg
• Any wheel on which the parking brake operates does not lock - 16% of design GVW

So, what next?

Ensure your maintenance provider knows how to properly read the roller brake test correctly. Make sure they aren’t just giving the vehicle a ‘pass’ without highlighting issues that should be investigated! Your vehicle should not be released back onto the road if it is not roadworthy.

Change your service level agreement with the maintenance provider to ensure all roller brake tests are carried out with sufficient load. It may cost more if you need the maintenance provider to load the vehicles and trailers for you, and a lot of providers even charge per axle, but every time you get a brake test done that isn’t sufficiently loaded, you are just throwing your money away - it isn’t worth the piece of paper it is written on!

Have roller brake tests carried out every time the braking system has work carried out, not just four times per year. If you’ve just had new discs or pads put on your vehicle, wouldn’t you rather find out if they have been installed properly and are working efficiently on a roller brake machine before an accident happens and it’s too late?

Observe and analyse your brake test before you put your vehicle out on the road. As we have discussed, an overall result of a ‘pass’ is not always a pass. You must check every line on the test to ensure the vehicle you are putting on the road is safe.

If you would like to know more, please feel free to contact and we can discuss further!