Trail braking is a driving and motorcycle riding technique where the brakes are used beyond the entrance to a turn (turn-in), and then gradually released (trailed off). Depending on a number of factors, the driver fully releases brake pressure at any point between turn-in and the apex of the turn. [1] [2] [3] [4] [5]
In applying this technique, motorcycle riders approach turns applying 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 is done for several reasons.
First, it gives more traction because the downward force on the front tire is increased by load transfer. Second, as the brakes are applied and the weight shifts forward, the forks are compressed. [6] The compression of the forks changes the motorcycle's steering geometry, decreasing stability in a way that makes the motorcycle more apt to lean and more quickly change direction. Third, decreasing speed decreases the motorcycle's cornering radius. Conversely, accelerating while turning increases the motorcycle's cornering radius.
Fourth, trailing off the brakes while entering blind or tight corners allows the rider to slow if something unexpected blocks the rider's path. Because the motorcycle is already on the brakes and the front tire is getting additional traction from already slowing, the rider can slow even more with very little risk, depending on surface conditions. However, applying the brakes after the motorcycle is already leaned over can be risky, depending on surface conditions and lean angle.
Traditionally, trail braking is done exclusively with the front brake, even though trailing the rear brake will also effectively slow the motorcycle and decrease the turning radius. [7]
The rider's ability to correctly choose their turn in, apex, and exit points reduces or eliminates the need for prolonged trailing of the brakes into turns. This technique is commonly used when racing, but can enhance control, increase sight distance through the turn, and add evasive options for street riders.
There is risk with trail braking because excessive use of the front brake can result in a loss of grip as the tire's adhesion is split between braking and cornering forces. [6] Effective trail braking requires finesse from the rider, which can be difficult to learn. [6]
Motorcycle training curriculums vary in whether they introduce trail braking to beginning street riders, or focus on other skills at first and introduce the topic to intermediate riders later.
Guides such as the Motorcycle Safety Foundation Basic RiderCourse teach that the safest way for a beginning rider to approach a corner on a motorcycle is by doing all slowing, whether with brakes or engine, before the entrance of the turn, discouraging the use of any brakes while the motorcycle is leaned over. [6] [8] The reasons for not trail braking on the street, at least for beginners, include that the steep learning curve of trail braking makes it appropriate only for the race track. The benefit of learning trail braking to the street rider is that knowing and understanding how to slow while entering a corner gives a greater safety margin, particularly in blind, decreasing radius or downhill corners.
Freddie Spencer, founder of the Freddie Spencer's High Performance Riding School, as well as Nick Ienatsch, author of the 2003 book Sport Riding Techniques and chief instructor of Yamaha Champions Riding School, say trail braking should be used in nearly every corner as a means to help the motorcycle change direction, and that trail braking gives the rider more control and significantly increases rider safety. [9] [10]
Spencer and Ienatsch say the physics of angular acceleration mean that the slower any vehicle is going, the tighter the radius of the corner it can navigate. [9] Instructor Keith Code said that, as soon as possible after initiating a turn, the rider should increase throttle smoothly and progressively throughout the turn. [11] Spencer said that for every radius, motorcycle, and rider combination there is a maximum speed at which the turn can be navigated without exiting the road or suffering a low side crash. Code is saying that as long as this maximum speed is not exceeded, proper throttle control throughout the turn will result in higher corner exit speeds and faster lap times.
In four wheel vehicles trail braking is using the brakes past the corner entrance, as opposed to the normally taught practice of releasing the brakes before starting the turn. It creates weight transfer to the front tires, increasing their traction and reducing understeer. It works best in light vehicles that have their brake bias to the front.
In order to be properly performed, the driver must have excellent sense of the vehicle's behavior and be able to keep the braking effort within very tight limits. Excessive braking effort may result in the vehicle heavily understeering, or — if the brake bias is set to nearly neutral — in the rear wheels locking, effectively causing the vehicle to spin as in a handbrake turn.
Mastering trail braking can help a driver enter corners at higher speeds, or help avoid an accident if the driver has entered a corner at a speed exceeding the abilities of either the driver or the vehicle.
There are two reasons for trail braking: [1]
A side benefit of trail braking — although this should not be considered a reason for using it — is that it often allows the driver to begin to brake later, since they are ending the braking later.
Trail braking is not used in every corner. [5] There are turns, especially very fast ones, where the driver wants to be squeezing back on the throttle about the time they are turning into the corner, since this helps the car's balance and the overall grip level. As a general rule, the slower and tighter the turn, the more the driver will use trail braking to help rotate the car; the faster and more sweeping the turn, the less the driver will use trail braking. [12]
A drift-inducing technique called "the brake drift" is used in racing, involving a series of light rear brake trail-braking pulses (usually 2 or 3), followed by a momentary full-force rear braking and sharp releasing of the rear brakes. Mastering continuous trail braking as used under road conditions is a prerequisite for learning brake drifting. This is one of the most used drifting techniques in rally racing because - if done properly - it allows the driver to enter and exit the corner with full throttle.
Depending upon cornering situations, techniques like trail braking can be used to maintain more speed upon entry of a corner, and attaining more grip while turning into the corner, and has an effect on apex selection. In this technique, brake pressure is applied slightly later than usual upon deceleration, and is maintained during steering input, sometimes all the way to the apex. The action of braking causes a weight transfer in the vehicle, shifting more weight from the rear of the car forward to the front tires, increasing the normal force on them and in turn increasing the amount of traction the front (steering) wheels have. Because of the characteristics of weight transfer, this technique causes weight to be shifted away from the rear of the car, resulting in lower rear traction, and can be used to induce oversteer in some cases.
As compared to the traditional circular entry, trail braking reduces the time for the requisite direction change needed to reach the driver's chosen apex. [13] With the traditional corner entry where all deceleration is completed prior to steering input, the vehicle carries a constant speed and radius to the apex. The combined peak tire forces act on the car perpendicular to its direction of travel to accelerate it toward its current turn center. The vehicle takes a circular path to the apex at a constant speed.
In comparison, trail braking splits up the peak force the tire is able to generate partially toward braking (longitudinal force acting on a tangent to the direction of travel), and partially toward steering (lateral force acting perpendicular to direction of travel). See the traction circle for more info. The combined vector force acting on the vehicle's center of gravity accelerates it in a more rearward direction as shown in the illustration. This causes the vehicle to travel on an Euler spiral-shaped path of constant radius and speed reduction.
An anti-lock braking system (ABS) is a safety anti-skid braking system used on aircraft and on land vehicles, such as cars, motorcycles, trucks, and buses. ABS operates by preventing the wheels from locking up during braking, thereby maintaining tractive contact with the road surface and allowing the driver to maintain more control over the vehicle.
Left-foot braking is the technique of using the left foot to operate the brake pedal in an automobile, leaving the right foot dedicated to the throttle pedal. It contrasts with the practice of using the left foot to operate the clutch pedal, leaving the right foot to share the duties of controlling both brake and gas pedals.
Opposite lock, also commonly known as countersteer, is a colloquial term used to mean the steering associated with the deliberate use of oversteer to turn a vehicle rapidly without losing momentum. It is typified by the classic rallying style of rear-wheel drive cars, where a car travels around a bend with a large drift angle. The terms "opposite lock" and "counter-steering" refer to the position of the steering wheel during the maneuver, which is turned in the opposite direction to that of the bend.
A traction control system (TCS), also known as ASR, is typically a secondary function of the electronic stability control (ESC) on production motor vehicles, designed to prevent loss of traction of the driven road wheels. TCS is activated when throttle input and engine power and torque transfer are mismatched to the road surface conditions.
In vehicle dynamics, slip angle or sideslip angle is the angle between the direction in which a wheel is pointing and the direction in which it is actually traveling. This slip angle results in a force, the cornering force, which is in the plane of the contact patch and perpendicular to the intersection of the contact patch and the midplane of the wheel. This cornering force increases approximately linearly for the first few degrees of slip angle, then increases non-linearly to a maximum before beginning to decrease.
Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occurs when a car steers less than the amount commanded by the driver.
Automobile handling and vehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly during cornering, acceleration, and braking as well as on the vehicle's directional stability when moving in steady state condition.
A highsider, or as it's more commonly referred to, a high-side, is a type of motorcycle accident characterized by sudden and violent rotation of the bike around its long axis. This generally happens when the rear wheel loses traction, skids, and then suddenly regains traction, creating a large torque which flips the rider head first off the side of the motorcycle or over the handlebars.
A locking differential is a mechanical component, commonly used in vehicles, designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction available to either wheel individually.
Aquaplaning or hydroplaning by the tires of a road vehicle, aircraft or other wheeled vehicle occurs when a layer of water builds between the wheels of the vehicle and the road surface, leading to a loss of traction that prevents the vehicle from responding to control inputs. If it occurs to all wheels simultaneously, the vehicle becomes, in effect, an uncontrolled sled. Aquaplaning is a different phenomenon from when water on the surface of the roadway merely acts as a lubricant. Traction is diminished on wet pavement even when aquaplaning is not occurring.
Countersteering is used by single-track vehicle operators, such as cyclists and motorcyclists, to initiate a turn toward a given direction by momentarily steering counter to the desired direction. To negotiate a turn successfully, the combined center of mass of the rider and the single-track vehicle must first be leaned in the direction of the turn, and steering briefly in the opposite direction causes that lean. The rider's action of countersteering is sometimes referred to as "giving a steering command".
Lift-off oversteer is a form of sudden oversteer. While cornering, a driver who closes the throttle, usually at a high speed, can cause such sudden deceleration that the vertical load on the tires shifts from rear to front, in a process called load transfer. This decrease in vertical load on the rear tires in turn decreases their traction by lowering their lateral force, making the vehicle steer more tightly into the turn. In other words, easing off the accelerator in a fast turn can cause a car's rear tires to loosen their grip so much that the driver loses control and drifts outwards, even leaving the road tailfirst.
In motorsport, the racing line is the optimal path around a race course. In most cases, the line makes use of the entire width of the track to lengthen the radius of a turn: entering at the outside edge, touching the "apex"—a point on the inside edge—then exiting the turn by returning outside.
Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics falls under a branch of physics known as classical mechanics. Bike motions of interest include balancing, steering, braking, accelerating, suspension activation, and vibration. The study of these motions began in the late 19th century and continues today.
A motorcycle's suspension serves a dual purpose: contributing to the vehicle's handling and braking, and providing safety and comfort by keeping the vehicle's passengers comfortably isolated from road noise, bumps and vibrations.
A wheelspin occurs when the force delivered to the tire tread exceeds that of available tread-to-surface friction and one or more tires lose traction. This leads the wheels to "spin" and causes the driver to lose control over the tires that no longer have grip on the road surface. Wheelspin can also be done intentionally such as in drifting or doing a burnout.
Motorcycle components and systems for a motorcycle are engineered, manufactured, and assembled in order to produce motorcycle models with the desired performance, aesthetics, and cost. The key components of modern motorcycles are presented below.
A motorcycle tyre is the outer part of motorcycle wheel, attached to the rim, providing traction, resisting wear, absorbing surface irregularities, and allowing the motorcycle to turn via countersteering. The two tyres' contact patches are the motorcycle's connection to the ground, and so are fundamental to the motorcycle's suspension behaviour, and critically affect safety, braking, fuel economy, noise, and rider comfort.
The following is a glossary of terminology used in motorsport, along with explanations of their meanings.
An automobile skid is an automobile handling condition where one or more tires are slipping relative to the road, and the overall handling of the vehicle has been affected.
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