Editing Electronic stability control (section)

== Concept and operation ==
{{main|Directional stability}}
During normal driving, ESC continuously monitors steering and vehicle direction. It compares the driver's intended direction (determined by the measured steering wheel angle) to the vehicle's actual direction (determined through measured lateral acceleration, vehicle rotation, and individual road wheel speeds).

===Normal operation===
ESC intervenes only when it detects a probable loss of steering control, such as when the vehicle is not going where the driver is steering.<ref>{{cite web |url=http://www.iihs.org/research/qanda/esc.html |title=Q&As: Electronic Stability Control |publisher=Iihs.org |access-date=2011-11-13 |archive-date=2011-11-02 |archive-url=https://web.archive.org/web/20111102202059/http://www.iihs.org/research/qanda/esc.html |url-status=dead }}</ref> This may happen, for example, when skidding during emergency evasive swerves, understeer or oversteer during poorly judged turns on slippery roads, or [[hydroplaning (tires)|hydroplaning]]. During high-performance driving, ESC can intervene when unwanted, because steering input may not always be indicative of the intended direction of travel (such as during controlled [[Drifting (motorsport)|drifting]]). ESC estimates the direction of the skid, and then applies the brakes to individual wheels asymmetrically in order to create torque about the vehicle's vertical axis, opposing the skid and bringing the vehicle back in line with the driver's commanded direction. Additionally, the system may reduce engine power or operate the transmission to slow the vehicle down.

ESC can function on any surface, from dry pavement to frozen lakes.<ref>{{cite web|url=https://www.youtube.com/watch?v=AHvoPJrXIMU  |archive-url=https://ghostarchive.org/varchive/youtube/20211212/AHvoPJrXIMU| archive-date=2021-12-12 |url-status=live|title=Truck ESP System |publisher=YouTube |date=2007-06-04 |access-date=2011-11-13}}{{cbignore}}</ref><ref name=autogenerated3>{{cite web|url=https://www.youtube.com/watch?v=K3m24bjkfg0  |archive-url=https://ghostarchive.org/varchive/youtube/20211212/K3m24bjkfg0| archive-date=2021-12-12 |url-status=live|title=How Effective is Stability Control |publisher=YouTube |date=2007-04-10 |access-date=2011-11-13}}{{cbignore}}</ref> It reacts to and corrects skidding much faster and more effectively than the typical human driver, often before the driver is even aware of any imminent loss of control.<ref>{{cite web |url=http://www.toyota.com/help/glossary.html#v |title=Toyota Glossary |publisher=Toyota.com |access-date=2011-11-13 |url-status=dead |archive-url=https://web.archive.org/web/20110415163840/http://www.toyota.com/help/glossary.html#v |archive-date=2011-04-15 }}</ref> This has led to some concern that ESC could allow drivers to become overconfident in their vehicle's handling and/or their own driving skills. For this reason, ESC systems typically alert the driver when they intervene, so that the driver is aware that the vehicle's handling limits have been reached. Most activate a dashboard indicator light<ref>{{Cite web |last=Worner |first=Randy |date=December 17, 2022 |title=Service StabiliTrak Light: Meaning and How To Reset It |url=https://chevygeek.com/service-stabilitrak/ |website=Chevy Geek}}</ref> and/or alert tone; some intentionally allow the vehicle's corrected course to deviate very slightly from the driver-commanded direction, even if it is possible to more precisely match it.<ref>{{cite journal|title=Tseng, H.E.; Ashrafi, B.; Madau, D.; Allen Brown, T.; Recker, D.; The development of vehicle stability control at Ford |doi=10.1109/3516.789681 |publisher=[[IEEE]] |date=2002-08-06 }}</ref>

All ESC manufacturers emphasize that the system is not a performance enhancement nor a replacement for safe driving practices, but rather a safety technology to assist the driver in recovering from dangerous situations. ESC does not increase traction, so it does not enable faster cornering (although it can facilitate better-controlled cornering). More generally, ESC works within the limits of the vehicle's handling and available traction between the tyres and road. A reckless maneuver can still exceed these limits, resulting in loss of control. For example, during hydroplaning, the wheels that ESC would use to correct a skid may lose contact with the road surface, reducing its effectiveness.

Due to the fact that stability control can be incompatible with high-performance driving, many vehicles have an override control which allows the system to be partially or fully deactivated. In simple systems, a single button may disable all features, while more complicated setups may have a multi-position switch or may never be fully disengaged.

=== Off-road use ===
ESC systems—due to their ability to enhance vehicle stability and braking—often work to improve traction in off-road situations, in addition to their on-road duties. The effectiveness of traction control systems can vary significantly, due to the significant number of external and internal factors involved at any given time, as well as the programming and testing performed by the manufacturer.

At a rudimentary level, off-road traction varies from typical operational characteristics of on-road traction, depending on the terrain encountered. In an open differential setup, power transfer takes the path of least resistance. In slippery conditions, this means when one wheel loses traction, power will counter-productively be fed to that axle instead of the one with higher grip. ESCs focus on braking wheels that are spinning at a rate drastically different from the opposing axle. While on-road application often supplements rapidly intermittent wheel braking with a reduction of power in loss-of-traction situations, off-road use will typically require consistent (or even increased) power delivery to retain vehicle momentum while the vehicle's braking system applies intermittent braking force over a longer duration to the slipping wheel until excessive wheel-spin is no longer detected.

In intermediate level ESC systems, ABS will be disabled, or the computer will actively lock the wheels when brakes are applied. In these systems, or in vehicles without ABS, the performance in emergency braking in slippery conditions is greatly improved as grip state can change extremely rapidly and unpredictably off-road when coupled with inertia. When the brakes are applied and wheels are locked, the tyres do not have to contend with the wheel rolling (providing no braking force) and braking repeatedly. Grip provided by the tyres is constant and as such can make full use of traction wherever it is available. This effect is enhanced where more aggressive tread patterns are present as the large tread lugs dig into the imperfections on the surface or below the substrate, as well as dragging dirt in front of the tyre to increase the rolling resistance even further.

Many newer vehicles designed for off-road duties from the factory, are equipped with Hill Descent Control systems to minimise the risk of such runaway events occurring with novice drivers and provide a more consistent and safe descent than either no ABS, or on-road orientated ABS. These systems aim to keep a fixed speed (or user selected speed) while descending, applying strategic braking or acceleration at the correct moments to ensure wheels all rotate at the same rate while applying full locking braking when required.

In some vehicles, ESC systems automatically detect whether to operate in off- or on-road mode, depending on the engagement of the 4WD system. Mitsubishi's unique Super-Select 4WD system (found in Pajero, Triton and Pajero Sport models), operates in on-road mode in 2WD as well as 4WD High-range with the centre differential unlocked. However, it automatically activates off-road traction control and disables ABS braking when shifted into 4WD High-range with centre differential locked, or 4WD Low-range with centre differential locked. Most modern vehicles with fully electronically controlled 4WD systems such as various Land Rovers and Range Rovers, also automatically switch to an off-road-orientated mode of stability and traction control once low range, or certain terrain modes are manually selected.