question: Why would automakers put a limited slip differential in a sports car over a locked differential or a positrac
comment: You've got some major confusion here. A limited slip and a posi are the same thing. GM just trademarked the name positraction so others can't use it. A locking differential is better for offroading due to ensuring that both wheels turn in unison so if one wheel slips the other can pick up the slack.
passages: Section::::Applications.
  
  BULLET::::- Race cars often use locking differentials in order to maintain traction during high speed maneuvers or when accelerating at extreme rates. Additionally, vehicle dynamics are made more predictable when there is a loss of traction, as the driver knows that neither wheel will suddenly sap power if it encounters a low-friction surface.
   BMW's electronic limited-slip differential used on the F10 5 Series is an example of such a system. Another example began on the first year (1992) production of the re-styled, and new 4.6L V-8 overhead cam Ford Crown Victoria model with its optional anti-lock brakes. This option was available on the 1992 Crown Victoria, onward; on those cars equipped with anti-lock brakes.
  
  Section::::Types.:Other related final drives.
  
  BULLET::::- Spool
  
  BULLET::::- Locking differential
  
  Section::::Factory names.
   An alternative is to use the natural separation force of the gear teeth to load the clutch. An example is the center differential of the 2011 Audi Quattro RS 5.
   BULLET::::- Mercedes: ASD, AMG Rear-Axle Differential Lock (active differential on select FR-based AMG/S models; pure mechanical variant also present on select non-S AMG models)
  
  Section::::In popular culture.
  
  In The Beach Boys' song "409", the lyrics mention the presence of a limited-slip differential: "...My four-speed, dual-quad, Positraction 4-0-9 (4-0-9, 4-0-9)."
   BULLET::::- Hyundai: HTRAC
  
  BULLET::::- International: Trak-Lok (clutches only) or Power-Lok (clutch and ramping engagement process)
  
  BULLET::::- Jeep: Trac-Lok (clutch-type mechanical), Tru-Lok (gear-type mechanical), and Vari-Lok (gerotor pump), Power Lok
  
  BULLET::::- Lincoln: Directed Power
  
  BULLET::::- Maserati: Equ-Tor
  
  BULLET::::- Nissan: GT LSD
  
  BULLET::::- Oldsmobile: Anti-Spin
  
  BULLET::::- Pontiac: Safe-T-Track
  
  BULLET::::- Porsche: PSD (electro-hydraulic mechanical), Porsche Torque Vectoring/Plus (PTV/Plus, combined electro-hydraulic mechanical and brake-based type; rear axle only)
  
  BULLET::::- Saab: Saab XWD eLSD
  
  BULLET::::- Studebaker-Packard Corporation: Twin Traction
  
  BULLET::::- Toyota: LSD
  
  BULLET::::- TVR: Hydratrak
  
  BULLET::::- Yukon Gear & Axle: Duragrip
   Section::::Alternatives.
  
  Limited-slip differentials are considered a compromise between a standard differential and a locking differential because they operate more smoothly, and they do direct some extra torque to the wheel with the most traction compared to a standard differential, but they are not capable of 100% lockup.
   Francis and Colotti knew the shortage of limited slip differential manufacturers was a big hardship experienced by Grand Prix constructors then. For example, Colin Chapman had his in-house engineers, Keith Duckworth and Mike Costin, develop the sequentially shifting transaxles for Lotus 16 and Lotus 18, which he had originally asked Richard Ansdale and Harry Mundy to design for Lotus 12. But despite these transaxles being unique and innovative, they still incorporated limited slip differentials made by ZF of Germany, which was about the only source, and the technology used was an old slip-limiting principle invented by Ferdinand Porsche in the 1930s for Auto Union GP cars.
   An electronic limited-slip differential will typically have a planetary or bevel gear set similar to that of an open differential and a clutch pack similar to that in a torque sensitive or gerotor pump based differential. In the electronic unit the clamping force on the clutch is controlled externally by a computer or other controller. This allows the control of the differential’s limiting torque, "Trq", to be controlled as part of a total chassis management system. An example of this type of differential is Subaru’s DCCD used in the 2011 Subaru WRX STi. Another example is the Porsche PSD system used on the Porsche 928. A third example is the SAAB XWD (Haldex Generation 4) with eLSD, it uses a common (electronically controlled via the vehicle computer network) hydraulic power pack to control both the longitudinal and transversal torque transfer of the XWD system. The same Haldex system is used on several other GM Epsilon based vehicles such as the Cadillac SRX etc.
   In 1932, Ferdinand Porsche designed a Grand Prix racing car for the Auto Union company. The high power of the design caused one of the rear wheels to experience excessive wheel spin at any speed up to . In 1935, Porsche commissioned the engineering firm ZF to design a limited-slip differential to improve performance. The ZF "sliding pins and cams" became available, and one example was the Type B-70 used during the Second World War in the military VWs (Kübelwagen and Schwimmwagen), although technically this was not a limited-slip differential, but a system composed of two freewheels, which sent the whole of the engine power to the slower-turning of the two wheels.
   The main advantage of a limited-slip differential is demonstrated by considering the case of a standard (or "open") differential in off-roading or snow situations where one wheel begins to slip. In such a case with a standard differential, the slipping or non-contacting wheel will receive the majority of the power (in the form of low-torque, high rpm rotation), while the contacting wheel will remain stationary with respect to the ground. The torque transmitted by an open differential will always be equal at both wheels; if one tire is on a slippery surface, the supplied torque will easily overcome the available traction at a very low number. For example, the right tire might begin to spin as soon as of torque is placed on it, since it is on an icy surface. Since the same amount of torque is always felt at both wheels, regardless of the speed at which they are turning, this means that the wheel with traction cannot receive more than 70 Nm of torque either, which is far less than is required to move the vehicle. Meanwhile, the tire on the slippery surface will simply spin, absorbing all of the actual "power" output (which is a function of torque provided over time), even though both wheels are provided the same (very low) amount of torque. In this situation, a limited-slip differential prevents excessive power from being allocated to one wheel, and so keeps both wheels in powered rotation, ensuring that the traction will not be limited to the wheel which can handle the minimum amount of power. 
   However, as the development process continued, engineers at BorgWarner discovered that, with clever software programming, they could control the variable electromagnetic multi-disc clutch to a point where it would allow the front and rear drive shafts to turn at different rotational speeds on its own, without the aid of a planetary or bevel geared center differential. In "Auto mode" the new software algorithms allowed the multi-disc clutch pack's friction and clutch discs to slip as needed, simulating a planetary or bevel geared center differential, making a geared differential redundant. Thus, the geared differential was abandoned and therefore never included on the final production version of the four-wheel drive system.
   The advantages of LSD in high-power, rear wheel drive automobiles were demonstrated during the United States "Muscle-Car" era from the mid 1960s through the early 1970s. Cars of this era normally were rear wheel drive and did not feature independent suspension for the rear tires (but instead used a live axle). With a live axle, when high torque is applied through the differential, the traction on the right rear tire is lower as the axle naturally wants to turn with the torsion of the drive shaft (but is held stationary by being mounted to the vehicle frame). This coined the terms "one wheel peel" or "one tire fire". As such, "Muscle-Cars" with LSD or "posi" (posi-traction) were at a distinct advantage to their wheel-spinning counterparts.
   This type includes helical gear limited-slip differentials and clutch, cone (an alternative type of clutch) where the engagement force of the clutch is a function of the input torque applied to the differential (as the engine applies more torque the clutches grip harder and "Trq" decreases).
   AMG offered Torsen differentials as an option as early as 1988 for new as well as for retrofitting for 107, 116, 123, 126 series Mercedes Benz cars.
  
  Toyota Altezza (sold in U.S. and Canada as Lexus IS200 and IS300) came with a torsen differential. For Lexus models it was included with all models with manual transmission, optional factory equipped with automatic transmission. The Toyota Altezza was standard on all manual transmission SXE10 models (with the 5th-generation Beams 3S-GE engine and J160 6-speed manual transmission).
  
  Section::::Torsen applications.
  
  Section::::Torsen applications.:Center.
   Fully integrated active differentials are used on the Ferrari F430, Mitsubishi Lancer Evolution, Lexus RC F and GS F, and on the rear wheels in the Acura RL. A version manufactured by ZF is also being offered on the B8 chassis Audi S4 and Audi A4. The Volkswagen Golf GTI Mk7 in Performance trim also has an electronically controlled front-axle transverse differential lock, also known as VAQ.
  
  Section::::See also.
  
  BULLET::::- Ball differential
  
  BULLET::::- Equation clock
  
  BULLET::::- Hermann Aron#Electricity meters
  
  BULLET::::- Limited slip differential
  
  BULLET::::- Locking differential
  
  BULLET::::- Torque vectoring
  
  BULLET::::- Whippletree (mechanism)
  
  Section::::External links.
   A proposed alternate way to distribute power to the wheels, is to use the concept of a "gearless differential", about which a review has been reported by Provatidis, but the various configurations seem to correspond either to the "sliding pins and cams" type, such as the ZF B-70 available on early Volkswagens, or are a variation of the ball differential.
   Unlike other friction-based LSD designs that combine a common spider gear "open" differential in combination with friction materials that inhibit differentiation, the torque sensing design is a unique type of differential, with torque bias inherent in its design, not as an add-on. Torque bias is only applied when needed, and does not inhibit differentiation. The result is a true differential that does not bind up like LSD and locking types, but still gives increased power delivery under many road conditions.
  
  Examples include:
   Open centre differential, manually lockable via switch on centre console.¹
  
  Open rear differential, manually lockable via switch on centre console.¹
  
  Open front differential, no lock.
  
  ¹ABS disabled when locked.
   BULLET::::- Torsen T-1 is the brand name of the original Gleasman differential invented by Vernon Gleasman "circa" 1949 (US Patent 2,559,916 applied in 1949, granted 1951). The original Gleasman design was sold to The Gleason Works (later named Gleason Corporation), who started marketing it in 1982. The original T-1 model is incompatible with c-clip drive axles, which limited its use with many cars and pick-up trucks of the time. However, the original Torsen differential was used in racing by Mario Andretti and Paul Newman with great success. All later worm gear LSD designs were derived from the original Gleasman differential. The T-1 is original equipment in the Audi Quattro, Subaru Impreza WRX STI, Toyota Mega Cruiser and AM General HMMWV "Humvee".
   In 2012 the Dodge Caliber SRT4 was offered an aftermarket Quaife ATB helical gear limited slip differential upgrade via RealTune.
  
  The 2015-onward Lotus Evora 400 has been fitted with the Quaife ATB differential.
  
  The 2016 limited-run Mini John Cooper Works Challenge was equipped with a Quaife ATB Differential. 
  
  From 2017, versions of the Mk3 Ford Focus RS featured the Quaife ATB differential, including RS, Race Red and Heritage Editions.
  
  The 2018 Ford Fiesta ST is available with a Quaife ATB Limited Slip Differential as a factory fit option, as part of the Performance Pack.
  
  Section::::External links.
   One method for creating the clamping force is the use of a cam-ramp assembly such as used in a Salisbury/ramp style LSD. The spider gears mount on the pinion cross shaft which rests in angled cutouts forming cammed ramps. The cammed ramps are not necessarily symmetrical. If the ramps are symmetrical, the LSD is 2 way. If they are saw toothed (i.e. one side of the ramp is vertical), the LSD is 1 way. If both sides are sloped, but are asymmetric, the LSD is 1.5 way. (See the discussion of 2, 1.5 and 1 way below)
   BULLET::::1. The ability to set up a more stable torque distribution, with full locking whereas the Torsen can only provide a torque distribution up to the Torque Bias Ratio; i.e., the Crown Gear differential can lock fully, regardless of bias ratio. Unlike the Torsen, the Crown Gear differential doesn't operate like a limited slip differential and can operate, fully locked, with no traction on one output shaft.
  
  BULLET::::2. Easier integration into control electronics allowing four-wheel electronic torque vectoring with or without the active rear sport differential
   BULLET::::- Torsen T-2 was a new Gleasman design "circa" 1984 (US Patent application WO1984003745 A1) that is compatible with c-clip axles. The new design, along with a merger creating Zexel-Gleason U.S.A. increased Torsen availability for OEM and aftermarket applications. Variants include the T-2R, which includes a Positraction style clutch pack that gives preload for racing purposes; and the T-3, a dual differential intended for AWD applications. The T-2 is original equipment in many high performance cars and pick-up trucks.
   A limited-slip differential is available for high-output applications. GM has sourced Quaife's automatic torque biasing (ATB) torque-sensing (Torsen-style) differential, which is an all-mechanical geared unit that uses no clutch packs or preloading to transfer torque from one axle to the other. The torque transfer occurs automatically and gradually when one wheel loses traction. This type of differential can severely reduce the effects of torque-steer.
  
  Section::::Design.:Performance.
   BULLET::::- Quaife differential, sold under the name Automatic Torque Biasing Differential (ATB), covered by European Patent No. 130806A2. The Quaife version is most established in Europe and other markets other than the US, providing extensive aftermarket support for European and Japanese brand cars, especially front wheel drive and all-wheel drive applications. The Ford Focus RS uses the Quaife as original equipment.
  
presuppositions: Limited slip differential and locked differential are different things. Automakers put either a limited slip differential or a positrac in a sports car.
corrections: Limited slip differential and locked differential are the same things. Automakers put a limited slip differential or a positrac in a sports car but they're the same thing.
raw_presuppositions: Limited slip differential and locked differential are different things. Automakers put either a limited slip differential or a positrac in a sports car.
raw_corrections: Limited slip differential and locked differential are the same things. Automakers put a limited slip differential or a positrac in a sports car but they're the same thing.