UN R90: Why Replacement Brake Linings Are a Type-Approval Question
UN R90 governs replacement brake linings, drums and discs rather than vehicles. It exists because a friction material that behaves differently from the original changes brake balance, and brake balance is what a roller brake tester measures axle by axle.
What the regulation approves
UN Regulation No. 90 covers the approval of replacement brake lining assemblies, drum brake linings, and replacement discs and drums. The current text incorporates the 02 series of amendments, with Supplement 4 in force from 16 October 2018.
The scope is defined by what the part fits. Replacement brake lining assemblies are approved for friction brakes in braking systems of vehicles in categories M, N, L and O that hold a type approval under Regulation No. 13, No. 13-H or No. 78. Replacement drum brake linings, which are riveted to a shoe, are approved for categories M3, N2, N3, O3 and O4 under Regulation No. 13. Replacement discs and drums for M, N and O vehicles are covered, and discs for L1 to L5 vehicles under Regulation No. 78.
Two exclusions matter commercially. Parts fitted at the time of vehicle manufacture, and original replacement parts intended for servicing, are outside the regulation. So are the parts the text defines as special parts. A garage buying a lining is therefore dealing with two different products depending on whether it is an original part or an aftermarket equivalent.
Why the regulation exists at all
A friction material is not a commodity. Change its composition and you change how much torque it produces at a given pressure and temperature, how that torque fades when it gets hot, and how quickly it recovers. Those differences land on the vehicle as a change in brake balance between axles.
That is why R90 tests behaviour rather than dimensions. The annexes set requirements by vehicle category — Annex 3 for M1, M2 and N1; Annex 4 for M3, N2 and N3; Annexes 5 and 6 for trailer categories; Annex 7 for category L — and Annex 9 defines how friction behaviour is determined by machine testing. Packaging, marking, conformity of production and penalties for non-conformity complete the regime.
For an operator the consequence is simple. A lining with the right shape and the wrong friction behaviour can pass a visual inspection and still leave a vehicle with a brake imbalance that only a brake tester will find.
How it shows up on an inspection lane
The brake tester is where an R90 problem becomes visible. A roller tester reports braking force per wheel, converts it to efficiency against the measured axle load, and shows the left-right difference on each axle. A lining that grabs or fades on one side produces exactly the pattern the test is designed to catch: adequate total force with an imbalance, or a service brake that passes cold and a parking brake that does not.
This is also why the brake tester has to capture axle load at the moment of test rather than carry a nominal figure from the plate. Efficiency is a ratio, and a wrong denominator turns a good brake into a failure or the reverse.
When a vehicle fails immediately after a lining replacement, the sequence to check is the part, then the fitting, then the adjustment. The approval mark on the part is the first thing to look at, because a lining outside R90 has no tested friction behaviour to appeal to.
Reading the mark
An approved replacement part carries an approval mark and approval data in the arrangement the regulation defines, together with the packaging requirements. The mark identifies the approval, and the approval is granted for a defined group of linings or discs rather than for a single part number.
For a buyer the practical check is that the part number on the box maps to an approval covering the axle it is being fitted to. A mark that exists but covers a different category group is not a valid answer, and it is the kind of detail an auditor picks up from a photograph.
What this means when you specify a brake tester
If your work includes fitting linings as well as testing vehicles, the brake tester is your quality gate. Specify it for the data an R90-related dispute needs, not just for a pass or fail lamp.
- Per-wheel braking force retained, so imbalance can be shown and not only flagged.
- Axle load measured during the test, used as the efficiency denominator.
- Brake input recorded — pedal force or circuit pressure — so the test conditions can be demonstrated.
- Test speed held and reported, so the method matches the one the regulation assumes.
- A report a third party can read without the operator explaining it.
Common questions
Does UN R90 approve vehicles or parts?
Parts. It approves replacement brake lining assemblies, drum brake linings, and replacement discs and drums as suitable for fitment to vehicles that already hold a type approval under Regulation No. 13, 13-H or 78. The vehicle approval and the replacement part approval are separate documents.
Are original manufacturer parts covered by R90?
No. Parts fitted during vehicle manufacture, and original replacement parts intended for servicing that vehicle, are excluded from the regulation scope. R90 exists for the aftermarket equivalent, which has to demonstrate friction behaviour comparable to the original.
Can a brake tester prove a lining complies with R90?
No. R90 compliance for the part is established by the approval tests, including machine testing of friction behaviour. A brake tester shows the result on the vehicle: efficiency per axle and left-right balance. The two are complementary — the approval predicts the behaviour, the tester confirms it on this vehicle.
Working to this requirement on a live project?
Send the vehicle classes, the daily volume and the standard the tender references. We will reply with the station list, the capacity each machine needs, and the report format the authority will accept.