A retarder is a device used to augment or replace some of the functions of primary friction-based braking systems, usually on heavy vehicles. Retarders serve to slow vehicles, or maintain a steady speed while traveling down a hill, and help prevent the vehicle from "running away" by accelerating down the hill. They are not usually capable of bringing vehicles to a standstill, as their effectiveness diminishes as vehicle speed lowers. They are usually used as an additional "assistance" to slow vehicles, with the final braking done by a conventional friction braking system. As the friction brake will be used less, particularly at higher speeds, their service life is increased, and since in those vehicles the brakes are air-actuated helps to conserve air pressure too.
Friction-based braking systems are susceptible to "brake fade" when used extensively for continuous periods, which can be dangerous if braking performance drops below what is required to stop the vehicle – for instance if a truck or bus is descending a long decline. For this reason, such heavy vehicles are frequently fitted with a supplementary system that is not friction-based.
Retarders are not restricted to road motor vehicles, but may also be used in railway systems. The British prototype Advanced Passenger Train (APT) used hydraulic retarders to allow the high-speed train to stop in the same distance as standard lower speed trains, as a pure friction-based system was not viable.
Friction-based braking systems are susceptible to "brake fade" when used extensively for continuous periods, which can be dangerous if braking performance drops below what is required to stop the vehicle – for instance if a truck or bus is descending a long decline. For this reason, such heavy vehicles are frequently fitted with a supplementary system that is not friction-based.
Retarders are not restricted to road motor vehicles, but may also be used in railway systems. The British prototype Advanced Passenger Train (APT) used hydraulic retarders to allow the high-speed train to stop in the same distance as standard lower speed trains, as a pure friction-based system was not viable.
by Huvudpersson July 24, 2017
Get the Retardermug. a mindset of deliberately rejecting overthinking and excessive self-analysis, choosing instead to live simply, act instinctively, and use one’s mind only for practical tasks rather than self-doubt or rumination.
After years of overthinking every decision, he finally started retard maxxing - just doing what needed to be done and not listening to the noise in his head.
by WomanPropagandist October 26, 2025
Get the retard maxxingmug. by HaKdogMen January 17, 2020
Get the Retardmug. 
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by DefenicionForIdiots January 23, 2021
Get the Retardmug. If you really have to look up retarded then your retarded (look it up in the dictionary you dumb ass)
by ক্লারা জেন November 3, 2019
Get the Retardedmug.