FMVSS 121 Air Brake Systems Vehicle Test Standard

FMVSS Standard 121 applies to trucks, buses and trailers equipped with air brake systems. It specifies the performance and equipment requirements for braking systems in vehicles equipped with air braking systems, including individually controlled parking brakes with prescribed holding capability, automatic brake adjusters and gauges, and emergency brakes that are automatically activated in the event of loss of air pressure.

Antilock brakes are required on new tractors with a GVWR over 10.000lbs (4.536kg). Antilock brakes are required on new trailers, single-unit trucks, and buses with a GVWR greater than 10.000 lbs (4.536 kg). From March 1997 the air compressor should activate automatically when the pressure in the air brake system drops below 100 psi.

This standard applies to trucks, buses and trailers equipped with air brake systems. However;

Any trailer that is greater than 102,36 inches in width and has extendable equipment in the fully retracted position and has two short track axles in a line across the width of the trailers, any vehicle equipped with an axle with a gross axle weight rating of 2 any truck or bus with a GVWR of more than 33 pounds and whose body complies with the definition of heavy tow trailers specified in S120.000. It does not apply to any trailer and any load divider dolly with an empty vehicle weight of not less than 4 percent of its GVWR.

Our EUROLAB testers provide a range of technical advice, certification and testing to help you achieve FMVSS compliance to ensure you can access the US automotive market. You can contact our laboratory for all FMVSS and FMVSS 121 test standards.