Lift-off oversteer

Last updated November 18, 2024

Lift-off oversteer (also known as , trailing-throttle oversteer, throttle off oversteer, or lift-throttle oversteer) is a form of sudden oversteer. While cornering, a driver who closes the throttle (by lifting a foot off the accelerator, hence the name), 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 (that perpendicular to the direction of travel), 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.

Dynamics

The graphs to the right show the simulated effect of lifting off the throttle in the middle of a left turn. The transients in the first couple of seconds are due to the test, in which a step steer input (wheel angle) is applied at 0 s and held constant throughout. The steady state cornering is at constant speed, with a lateral acceleration of 0.45 g approximately until the throttle is released at 6 s.

The yaw rate plot shows the oversteer due to the rear wheels losing traction - after an uncomfortable jerk at 20 deg/s, the vehicle spins sharply in the direction of the turn. The lateral acceleration also spikes to 0.6 g and levels at about 0.55 g, meaning that the radius decreased (i.e., the turn tightened). The side forces on the outside wheels increase and the inside rear (LR) wheel even lifts off the ground, a common occurrence.

Lift off oversteer is induced when the throttle is lifted while midway through a corner, often by inexperienced drivers who have entered the corner at an excessive speed.

Moment of inertia

Lift off oversteer is most common with mid-mounted engine, rear-wheel-drive (MR) vehicles.^{[ citation needed ]} Mid-mounted engine vehicles have a much lower rotational inertia than vehicles with a front-mounted or rear-mounted engine.^{[ citation needed ]} The lower rotational inertia of mid-mounted engine vehicles causes the vehicle to spin much faster than a front or rear mounted engine vehicle. If unexpected, it can catch the driver off guard when cornering, ultimately leading to loss of control of the vehicle.

Recovery

As in all situations where the vehicle experiences loss of rear tire traction on the road surface, the proper maneuver to recover is to turn the steering wheel in the opposite direction of the spin (Countersteering). e.g. If the front of the vehicle is spinning to the left, countersteering to the right will help recover control. More specifically aiming the wheels in the desired direction of travel. In the case of a very violent spin the safest thing to do is turn the wheel so the tires are pointing straight forward with respect to the vehicle. This is often easier to accomplish for inexperienced/panicked drivers.^[2]

Real life instances

Lift-off oversteer is often exploited in motorsport –particularly on loose surfaces (e.g. in rallying) –as a method of cornering faster as, when controlled, it has the effect of turning the nose into the apex and the car slightly sideways which allows early application of power on exiting the corner. Formula One driver Jim Clark's late-braking technique exploited the lift-off oversteer characteristics of mid-engined race cars to attain higher cornering speeds. It became standard competition driving technique as an enhancement of the four wheel drift technique that preceded it.

On April 10, 2010, Consumer Reports magazine rated the 2010 Lexus GX 460 SUV a "Don’t Buy: Safety Risk," as their panel of test engineers determined the vehicle was subject to excessive lift-off oversteer during a standardized evaluation for emergency handling. The test simulates scenarios such as transiting a highway exit ramp while traveling with excessive speed.^[3]

Related Research Articles

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.

Steering is the control of the direction of motion or the components that enable its control. Steering is achieved through various arrangements, among them ailerons for airplanes, rudders for boats, cylic tilting of rotors for helicopters, and many more.

A traction control system (TCS), 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.

Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of the vehicle to changes in steering angle associated with changes in lateral acceleration. This sensitivity is defined for a level road for a given steady state operating condition by the Society of Automotive Engineers (SAE) in document J670 and by the International Organization for Standardization (ISO) in document 8855. Whether the vehicle is understeer or oversteer depends on the rate of change of the understeer angle. The Understeer Angle is the amount of additional steering that must be added in any given steady-state maneuver beyond the Ackermann steer angle. The Ackermann Steer Angle is the steer angle at which the vehicle would travel about a curve when there is no lateral acceleration required.

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.

In automotive design, an RR, or rear-engine, rear-wheel-drive layout places both the engine and drive wheels at the rear of the vehicle. In contrast to the RMR layout, the center of mass of the engine is between the rear axle and the rear bumper. Although very common in transit buses and coaches due to the elimination of the drive shaft with low-floor buses, this layout has become increasingly rare in passenger cars.

A highsider or high-side is a type of motorcycle accident characterized by sudden and violent rotation of the bike around its longitudinal axis. This generally happens when the rear wheel loses traction, skids, and then suddenly regains traction, causing the rider to be thrown head-first from 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.

<span class="mw-page-title-main">Aquaplaning</span> Loss of traction due to water buildup under tires

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.

Drifting is a driving technique where the driver intentionally oversteers, with loss of traction, while maintaining control and driving the car through the entirety of a corner or a turn. The technique causes the rear slip angle to exceed the front slip angle to such an extent that often the front wheels are pointing in the opposite direction to the turn. Drifting is traditionally performed using three methods: clutch kicking, weight transfer, and employing a handbrake turn. This sense of drift is not to be confused with the four wheel drift, a classic cornering technique established in Grand Prix and sports car racing.

A tilting three-wheeler, tilting trike, leaning trike, or even just tilter, is a three-wheeled vehicle and usually a narrow-track vehicle whose body and or wheels tilt in the direction of a turn. Such vehicles can corner without rolling over despite having a narrow axle track because they can balance some or all of the roll moment caused by centripetal acceleration with an opposite roll moment caused by gravity, as bicycles and motorcycles do. This also reduces the lateral acceleration experienced by the rider, which some find more comfortable than the alternative. The narrow profile can result in reduced aerodynamic drag and increased fuel efficiency. These types of vehicles have also been described as "man-wide vehicles" (MWV).

The Lexus GX is a mid/full-size luxury SUV sold in North American and Eurasian markets by Lexus, a luxury division of Toyota. The GX is based on the Toyota Land Cruiser Prado, from which it derives its off-road capability.

<span class="mw-page-title-main">Trail braking</span> Driving and motorcycle riding technique where the brakes are used

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. Depending on a number of factors, the driver fully releases brake pressure at any point between turn-in and the apex of the turn.

Fishtailing is a vehicle handling problem which occurs when the rear wheels lose traction, resulting in oversteer. This can be caused by low-friction surfaces. Rear-drive vehicles with sufficient power can induce this loss of traction on any surface, which is called power-oversteer.

<span class="mw-page-title-main">Bicycle and motorcycle dynamics</span> Science behind the motion of bicycles and motorcycles

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.

The Scandinavian flick is a technique used predominantly in ice racing and rallying. The technique induces oversteer using weight transfer to carry a vehicle through a turn while simultaneously reducing speed.

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.

All Wheel Control (AWC) is the brand name of a four-wheel drive (4WD) system developed by Mitsubishi Motors. The system was first incorporated in the 2001 Lancer Evolution VII. Subsequent developments have led to S-AWC (Super All Wheel Control), developed specifically for the new 2007 Lancer Evolution. The system is referred by the company as its unique 4-wheel drive technology umbrella, cultivated through its motor sports activities and long history in rallying spanning almost half a century.

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.

References

↑ "How to Fix Understeer or Oversteer". 6 July 2015. Retrieved 18 January 2023.
↑ Belknap pg 46
↑ Consumer Reports (2010-04-13). "Don't Buy: Safety Risk--2010 Lexus GX 460". Cars Blog. Consumers Union. Archived from the original on 2010-04-15. Retrieved 2010-04-14.

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.

[1] "How to Fix Understeer or Oversteer". 6 July 2015. Retrieved 18 January 2023.

[2] Belknap pg 46

[3] Consumer Reports (2010-04-13). "Don't Buy: Safety Risk--2010 Lexus GX 460". Cars Blog. Consumers Union. Archived from the original on 2010-04-15. Retrieved 2010-04-14.

[1]

[2]

[3]