Motorcycle riders apply trail braking by approaching turns with front brakes to reduce speed. As they enter the turn, they slowly ease off the brakes, gradually decreasing or trailing off the brakes as motorcycle lean increases. This technique serves several purposes. First, it enhances traction because the downward force on the front tire increases due to load transfer. Second, as the brakes are applied and the weight shifts forward, the forks compress, altering the motorcycle's steering geometry. This compression decreases stability, making the motorcycle more apt to lean and change direction quickly. Third, decreasing speed reduces the motorcycle's cornering radius, while accelerating while turning increases it. Fourth, trailing off the brakes while entering blind or tight corners allows riders to slow down if unexpected obstacles appear. Since the motorcycle is already braking and the front tire has additional traction, riders can slow down further with minimal risk, depending on surface conditions. However, applying the brakes after the motorcycle is leaned over can be risky, depending on surface conditions and lean angle.
Traditionally, trail braking is done exclusively with the front brake, although trailing the rear brake also effectively slows the motorcycle and decreases the turning radius. A rider's ability to choose the correct turn-in, apex, and exit points minimizes the need for prolonged brake trailing into turns. This technique is commonly used in racing but can also enhance control, increase sight distance through the turn, and provide evasive options for street riders.
Trail braking carries risks, as excessive front brake use can lead to a loss of grip. The tire's adhesion is split between braking and cornering forces, making effective trail braking require finesse that can be difficult to learn.
Motorcycle training programs vary in their approach to teaching trail braking. Some guides, such as the Motorcycle Safety Foundation Basic RiderCourse, advise beginning riders to slow down before entering a turn, using brakes or engine braking before turning in. This approach discourages braking while the motorcycle is leaned over, citing the steep learning curve of trail braking as a reason to limit its use to race tracks. However, understanding and knowing how to slow down while entering a corner provides a greater safety margin, particularly in blind, decreasing radius, or downhill corners. Experienced instructors like Freddie Spencer and Nick Ienatsch advocate for using trail braking in nearly every corner to enhance control and rider safety.
In four-wheel vehicles, trail braking involves using the brakes past the corner entrance, unlike the conventional practice of releasing brakes before starting the turn. This technique creates weight transfer to the front tires, increasing their traction and reducing understeer. It is most effective in light vehicles with front-biased brake systems. To execute trail braking properly, drivers must have an excellent sense of the vehicle's behavior and maintain braking effort within tight limits. Excessive braking can lead to heavy understeer or, if the brake bias is nearly neutral, cause the rear wheels to lock and the vehicle to spin.
The primary reasons for trail braking are to keep load on the front tires, thereby increasing traction and reducing understeer, and to maximize tire traction throughout the corner. Trail braking also allows drivers to begin braking later, as they are ending the braking phase later. However, this technique is not suitable for every corner. In very fast turns, drivers often prefer to accelerate smoothly after turn-in to maintain balance and grip. As a general rule, trail braking is more useful in slower, tighter turns, while less useful in faster, sweeping turns.
In racing, a technique called "the brake drift" involves a series of light rear brake trail-braking pulses, usually 2 or 3, followed by a momentary full-force rear braking and sharp release of the rear brakes. Mastering trail braking is a prerequisite for learning brake drifting, a popular technique in rally racing. It allows drivers to enter and exit corners with full throttle. Trail braking can be used to maintain speed upon entry, attain more grip while turning, and influence apex selection. By applying brake pressure slightly later during deceleration and maintaining it during steering input, drivers can shift weight from the rear to the front tires, increasing traction.
Trail braking alters the traditional circular entry by splitting the peak tire force between braking and steering. This technique causes the vehicle to follow an Euler spiral-shaped path of constant radius and decreasing speed, rather than a circular path at constant speed. By optimizing the use of tire forces, trail braking enables more efficient direction changes and can be used to induce oversteer in certain situations.