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Road Users

Braking laws for Class R agricultural trailers and towed equipment 

Maximum design speeds, braking efficiency checks and manual slack adjusters.

This content is for general information only. It does not, and is not intended to, provide legal or technical advice or to represent a legal interpretation of the matters it addresses.


Frequently asked questions

See table below for braking laws applicable:

Maximum design speed of trailer is 40 km/h and DGVW* is less than 5 tonnesDesign speed of trailer is over 40 km/h & DGVW* is 5 tonnes or more
Service Brake - minimum brake efficiency of 25%Service Brake - minimum brake efficiency of 45%
Parking Brake - minimum brake efficiency of 16%Parking Brake - minimum brake efficiency of 16%
Breakaway brake - minimum brake efficiency of 13.5%Breakaway brake - minimum brake efficiency of 13.5%

*DGVW is the design gross vehicle weight, also referred to MAM (maximum authorised mass) on the trailer's plate is the weight of a vehicle or trailer including the maximum load it can carry as per the manufacturer's design specifications.

  • Trailers with a design speed of over 40 km/h that have been manufactured on or after 01 January 2016 must also be equipped with pneumatic braking systems including load-sensing capability.
  • Trailers with a design speed of over 60 km/h that have been manufactured on or after 01 January 2016 must be equipped with anti-lock braking systems (ABS).
  • Older trailers, provided they are designed to be drawn at speeds of 40 km/h or less can be fitted with a secondary coupling e.g., a chain or wire rope instead of a breakaway brake.

If your trailer or interchangeable towed equipment was manufactured before 01 January 2016 there is no requirement to retrofit ABS. If your trailer or interchangeable towed equipment was manufactured before 01 January 2016 there is no requirement to retrofit ABS.

Every new agricultural trailer manufactured on or after 01 January 2016 which is designed to be drawn at a speed over 60 km/h must be fitted with ABS complying with the construction and performance requirements of the General Safety Regulation 661 of 2009 as amended or of UN/ECE regulation 13.09. It is important to note that where the DGVW of the agricultural trailer is more than 10,000 kg a category A anti-lock braking system must be fitted. This is an ABS that controls the braking of the wheels independently on each side of the trailer.

You should contact the original trailer manufacturer or authorised Irish distributor. If the original manufacturer is no longer in business, you could contact another manufacturer of similar equipment who may be able to examine the vehicle to see what work if any needs to be done to achieve compliance for operation at speeds over 40 km/h.

You can take the vehicle to your local commercial vehicle roadworthiness test centre (CVRT) and get a brake test done. There will likely be a fee for this and is a private arrangement between you and the test centre.

Yes, but only for trailers or towed equipment with design speeds of 40 km/h or less or manufactured after 01 January 2016. Those with design speeds over 40 km/h and with a DGVW of more than 3.5 tonnes must be fitted with a pneumatic braking system and automatic slack adjusters whether or not a hydraulic braking system is also fitted. This is in compliance with the construction and performance requirements of the General Safety Regulation 661 of 2009 as amended.

If your tractor is designed to travel at speeds of 40km/h or less, you can draw a trailer with a laden weight of 5 tonnes or less without brakes. This is only the case if when laden the trailer does not exceed three times the tractor’s unladen weight.

Note: If your tractor is designed to travel at speeds over 40 km/h you can only draw a trailer with a laden weight of 3.5 tonnes without brakes