Highsider
Encyclopedia
A highsider or highside is a type of motorcycle
accident
characterized by sudden & violent rotation around the long axis of the motorcycle in the direction of travel. This generally happens when the bike is in a turn and the rear wheel loses traction, the bike rotates to tighten the turn around a vertical axis through the rider, the rear wheel slips as the turn tightens, skids as the turn tightens beyond the tire limit, speed is lost due to the slide and then the rear wheel stops skidding creating a large torque which then flips the bike down the road around the long axis, much as a boat will flip if turned too suddenly. The initial traction loss may be caused by a rear locked wheel due to excessive braking or by applying too much throttle when exiting a corner or by simply oversteering the bike in the turn, i.e. attempting to turn too sharply -rolling the bike over too far- and crossing the limit of tire adhesion: rolling off the edge of the sidewall, levering the rear tire off the ground with a scraped exhaust, peg, leg, foot or knee, or overstressing the rear tire if it is too cold or worn-out, or there is oil, water, sand or dirt on the road. Not so much that the rear-wheel washes-out and the bike falls down on its (low) side, but just enough to get it to slide and then catch suddenly. As a result highsides happen very quickly with little if any warning and are very violent.
If the slipping rear tire suddenly regains traction while the bike is side-slipping, the motorcycle will straighten-up very quickly. Often the rider is thrown off before they can regain balance & control.
Highside accidents are typically caused by over-acceleration or braking in corners, but also can result from simple overcornering in which the rear tire reaches its cornering-limit before the front tire or extended lock-up of the rear brake or wheelspin under acceleration combined with side-slip while traveling straight. In all cases, the rear-wheel begins to move out of the line of travel and side-slips. If the wheels are not aligned in the direction of travel when traction is suddenly restored and the rear-tire stops slipping then a highside is likely, depending on how much the bike is turned across the direction of travel and how fast the bike is traveling when the rear tire stops slipping. If the angle is high enough, the bike is moving fast enough and the rear tire slips & hooks-up suddenly enough, the rider has no chance of preventing a highside and not taking a short flight across hard ground. What makes the highside so deadly is that the bike can go from traveling down the road at high speed completely under control to tumbling down the road at high speed with the rider flying above it, all within a split second with little if any warning. Though really why this happens is simple to understand and easy to avoid.
occurring at the contact patch
. There is a limited amount of force that the contact patch can transmit before the tire begins to lose traction, and therefore slide/ skid.
When going through a curve on a motorcycle, centripetal force
(added to the other lateral forces such as acceleration or deceleration) is transferred from the road to the motorcycle through the contact patch, and is directed at a right angle to the path of travel. If the net force
is greater than the static friction coefficient of the tire multiplied by the normal force
of the motorcycle through the tire, the tire will skid outwards from the direction of the curve.
Once a tire slips in a curve, it will move outwards under the motorcycle. What happens from there depends on how well the rider is able to restore balance and control. If the tire regains traction
after the rider starts to skid while the motorcycle is moving sideways, the tire will stop its sideways movement causing the motorcycle to suddenly jerk into an upright position (and beyond). This movement can easily cause the rider to be thrown off and even expert riders are routinely thrown-off in highsides when they are caught riding a bike beyond its limits.
The name ("highside") derives from the side of the motorcycle that the rider will separate from. If forcibly thrown over the bike, the rider is said to have dismounted on the high side.
The highsider has the additional disadvantage of the rider often being catapulted quite some feet into the air by the sudden jerking motion of the motorbike and the increased possibility of damage upon impact with the ground as well as being hit by the motorbike that is tumbling, bouncing & sliding behind the rider, threatening to crush them. It is somewhat like being thrown from a horse at full-gallop, except that a motorcycle can travel much faster than a horse and are generally ridden on hard-paved roads with plenty of roadside obstacles.
Because highsider accidents are so much more deadly than lowside accidents, the Motorcycle Safety Foundation
recommends that if a rider locks the rear brake at higher speeds and the traction is good the brake should not be released.
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
accident
Accident
An accident or mishap is an unforeseen and unplanned event or circumstance, often with lack of intention or necessity. It implies a generally negative outcome which may have been avoided or prevented had circumstances leading up to the accident been recognized, and acted upon, prior to its...
characterized by sudden & violent rotation around the long axis of the motorcycle in the direction of travel. This generally happens when the bike is in a turn and the rear wheel loses traction, the bike rotates to tighten the turn around a vertical axis through the rider, the rear wheel slips as the turn tightens, skids as the turn tightens beyond the tire limit, speed is lost due to the slide and then the rear wheel stops skidding creating a large torque which then flips the bike down the road around the long axis, much as a boat will flip if turned too suddenly. The initial traction loss may be caused by a rear locked wheel due to excessive braking or by applying too much throttle when exiting a corner or by simply oversteering the bike in the turn, i.e. attempting to turn too sharply -rolling the bike over too far- and crossing the limit of tire adhesion: rolling off the edge of the sidewall, levering the rear tire off the ground with a scraped exhaust, peg, leg, foot or knee, or overstressing the rear tire if it is too cold or worn-out, or there is oil, water, sand or dirt on the road. Not so much that the rear-wheel washes-out and the bike falls down on its (low) side, but just enough to get it to slide and then catch suddenly. As a result highsides happen very quickly with little if any warning and are very violent.
If the slipping rear tire suddenly regains traction while the bike is side-slipping, the motorcycle will straighten-up very quickly. Often the rider is thrown off before they can regain balance & control.
Highside accidents are typically caused by over-acceleration or braking in corners, but also can result from simple overcornering in which the rear tire reaches its cornering-limit before the front tire or extended lock-up of the rear brake or wheelspin under acceleration combined with side-slip while traveling straight. In all cases, the rear-wheel begins to move out of the line of travel and side-slips. If the wheels are not aligned in the direction of travel when traction is suddenly restored and the rear-tire stops slipping then a highside is likely, depending on how much the bike is turned across the direction of travel and how fast the bike is traveling when the rear tire stops slipping. If the angle is high enough, the bike is moving fast enough and the rear tire slips & hooks-up suddenly enough, the rider has no chance of preventing a highside and not taking a short flight across hard ground. What makes the highside so deadly is that the bike can go from traveling down the road at high speed completely under control to tumbling down the road at high speed with the rider flying above it, all within a split second with little if any warning. Though really why this happens is simple to understand and easy to avoid.
Technical explanation
Forces occurring between the motorcycle and the road (such as accelerating, decelerating and turning) are transmitted by frictionFriction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
occurring at the contact patch
Contact patch
Contact patch is the portion of a vehicle's tire that is in actual contact with the road surface. It is most commonly used in the discussion of pneumatic tires, , where the term is strictly used to describe the portion of the tire’s tread that touches the road surface...
. There is a limited amount of force that the contact patch can transmit before the tire begins to lose traction, and therefore slide/ skid.
When going through a curve on a motorcycle, centripetal force
Centripetal force
Centripetal force is a force that makes a body follow a curved path: it is always directed orthogonal to the velocity of the body, toward the instantaneous center of curvature of the path. The mathematical description was derived in 1659 by Dutch physicist Christiaan Huygens...
(added to the other lateral forces such as acceleration or deceleration) is transferred from the road to the motorcycle through the contact patch, and is directed at a right angle to the path of travel. If the net force
Net force
In physics, net force is the total force acting on an object. It is calculated by vector addition of all forces that are actually acting on that object. Net force has the same effect on the translational motion of the object as all actual forces taken together...
is greater than the static friction coefficient of the tire multiplied by the normal force
Normal force
In mechanics, the normal force F_n\ is the component, perpendicular to the surface of contact, of the contact force exerted on an object by, for example, the surface of a floor or wall, preventing the object from penetrating the surface.The normal force is one of the components of the ground...
of the motorcycle through the tire, the tire will skid outwards from the direction of the curve.
Once a tire slips in a curve, it will move outwards under the motorcycle. What happens from there depends on how well the rider is able to restore balance and control. If the tire regains traction
Traction
- Engineering :*Forces:** Traction , adhesive friction or force in the context of vehicle** Traction vector, in mechanics, the force per unit area on a surface, including normal and shear components...
after the rider starts to skid while the motorcycle is moving sideways, the tire will stop its sideways movement causing the motorcycle to suddenly jerk into an upright position (and beyond). This movement can easily cause the rider to be thrown off and even expert riders are routinely thrown-off in highsides when they are caught riding a bike beyond its limits.
The name ("highside") derives from the side of the motorcycle that the rider will separate from. If forcibly thrown over the bike, the rider is said to have dismounted on the high side.
The highsider has the additional disadvantage of the rider often being catapulted quite some feet into the air by the sudden jerking motion of the motorbike and the increased possibility of damage upon impact with the ground as well as being hit by the motorbike that is tumbling, bouncing & sliding behind the rider, threatening to crush them. It is somewhat like being thrown from a horse at full-gallop, except that a motorcycle can travel much faster than a horse and are generally ridden on hard-paved roads with plenty of roadside obstacles.
Because highsider accidents are so much more deadly than lowside accidents, the Motorcycle Safety Foundation
Motorcycle Safety Foundation
The Motorcycle Safety Foundation is a United States national, not-for-profit organization, founded in 1973, and sponsored by the U.S. manufacturers and distributors of BMW, Ducati, Harley-Davidson, Honda, Kawasaki, KTM, Piaggio/Vespa, Suzuki, Triumph, Victory and Yamaha motorcycles...
recommends that if a rider locks the rear brake at higher speeds and the traction is good the brake should not be released.