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Braking at the maximum level just before the tires lock up or ABS activates. It means applying the brakes as hard as possible while maintaining control, achieving the shortest stopping distance.
Threshold braking means applying maximum brake force without exceeding the tires' grip limit — stopping in the shortest possible distance while maintaining steering control. In a car without ABS, this means staying just below lockup. In a car with ABS, it means pressing firmly enough to activate ABS without hesitation.
The "threshold" is the point just before the tires lock up or skid. At this threshold, the tire is still rolling but is at maximum deceleration slip — the optimal grip state. Past the threshold, the tires lock and both braking efficiency and steering control drop sharply.
Executing true threshold braking requires a firm, confident initial application — often described as "getting on the brake hard, fast." The common beginner mistake is a tentative, gradually increasing brake application that never reaches the threshold before the braking zone is used up.
Anatomy of a Corner (Lowum) explains: "Often referred to as threshold braking, your goal is to be on the very edge (hence threshold) of ABS activation or wheel lockup. The tires are what actually slow the car down — the brakes are simply the mechanism initiating deceleration. If you are braking at the tires' limit of adhesion, you are decelerating at the maximum possible rate. This equates to the minimum amount of time on the brakes, as well as the shortest possible distance. Every extra second you spend with your foot on the brake is time you could be spending at full throttle." Limpert's Brake Design and Safety provides the engineering precision: a tire goes "from peak friction to sliding friction in 0.167 seconds" and total time from brake application to lockup is approximately "0.389 seconds" — showing how narrow the threshold window actually is.