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The redline is the maximum engine speed at which an internal combustion engine or traction motor and its components are designed to operate without causing damage to the components themselves or other parts of the engine.^[1] The redline of an engine depends on various factors such as stroke, mass of the components, displacement, composition of components, and balance of components.

Redlining is riding or driving an automotive vehicle above the redline. The actual term redline comes from the red bars that are displayed on tachometers in cars starting at the rpm that denotes the redline for the specific engine. Straying into this area usually does not mean instant engine failure, but may increase the chances of damaging the engine.