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Limited Slip Vs Posi (List Of Differences)
Limited Slip and Posi are two terms that are often used interchangeably when it comes to differentials. Technically, they are both the same thing and Posi is just a slang word or different way to reference limited slip.
The name difference only references how the specific brand markets this component. The overall objective of limited slip is to reduce the risk of a slipping wheel. It’s aimed towards stabilizing rear wheels and rear tires. So let’s review limited slip differentials in more detail.
What Is Limited Slip Differential?
It is a type of automotive differential that limits the difference in torque between the two wheels on the same axle. This technology is used in a variety of vehicles, from sports cars to trucks and even some economy cars.
Unlike an open differential which freely allows the wheels to rotate at different speeds (thus, when one wheel is slipping, it will receive most of the torque, which isn't helpful), an LSD is designed to distribute the torque between the wheels proportionally.
How Does a Limited Slip Differential Work?
A Limited Slip Differential is a type of differential that's designed to help prevent loss of traction when one wheel begins to slip. It's a mechanical device that resides in the midpoint of the drive axle.
The differential's job is to take the torque from the engine and divide it between the wheels and the rear axle. In a traditional "open" differential, if one wheel loses traction and begins to spin, the differential will continue to feed power to that wheel because it's the path of least resistance.
This isn't ideal because it can leave the vehicle stuck if one wheel is on a slippery surface like ice or mud. Here's where the Limited Slip Differential comes in. The LSD is designed to sense when one wheel is spinning faster than the other.
It then uses a series of mechanical devices (in the most common type, a set of clutches and springs) to redistribute the engine's power to the wheel that has equal traction. It’s most noticeable on a rear-wheel drive car.
The clutch pack in an LSD is situated next to each drive wheel. When both wheels are turning at the same speed, the clutch pack doesn't engage, and power is evenly distributed toward the rear end.
But when one wheel starts to slip and spin faster, the clutch pack on that side of the differential engages due to the force exerted by the springs. This slows down the spinning wheel and sends more power to the other wheel, which helps maintain traction and keeps the vehicle moving forward.
What Vehicles Have Limited-Slip Differential?
Limited Slip Differentials (LSD) are typically found in performance cars, sport utility vehicles (SUVs), and trucks, but they can also be present in certain economy cars where better handling is desired. Here are some examples:
LSDs are common in sports cars and performance-oriented models due to their ability to improve handling and traction, especially during aggressive driving and cornering. Examples include the Chevrolet Corvette, Ford Mustang, BMW M-series, and Subaru WRX STI.
Sport Utility Vehicles (SUVs) and Trucks
Many SUVs and trucks, particularly those intended for off-road use, come with LSDs. They provide better traction on uneven terrain and slippery surfaces. Vehicles like the Toyota Land Cruiser, Jeep Wrangler, and Ford F-150 Raptor have LSDs.
Some economy cars and compact models might have LSDs, particularly on sportier trims or performance versions. For example, the Honda Civic Type R and the Mini Cooper S. They also have traction control in new models.
Some high-end luxury cars might have LSDs for better handling and performance. Examples include the Audi S and RS models and certain versions of Mercedes-Benz AMG models.
Keep in mind that whether a vehicle is equipped with an LSD can depend not only on the make and model but also on the specific trim level or optional packages. If you're interested in a specific vehicle and want to know if it has an LSD, it's best to check the vehicle's technical specifications or consult the dealership.
How Long Does A Limited Slip Differential Last?
A limited-slip differential generally lasts upwards of 100,000 miles under typical conditions. However, heavy-duty usage such as high-performance driving, towing, or off-roading can hasten wear and tear.
In addition, harsh driving conditions like extreme temperatures or rough terrains can contribute to a shorter lifespan. Regular maintenance, particularly changing differential oil as per manufacturer guidelines and using specified additives for clutch-type LSDs, can extend the LSD's longevity.
The quality of the components also matters, as higher-quality parts tend to outlast inferior ones. Despite these variations, any symptoms, such as unusual noises, vibrations, or handling issues, should prompt an inspection by a qualified mechanic to avoid potential damage.
Locking Vs. Limited Slip Differential
A locking differential and a limited-slip differential (LSD) are two types of mechanisms used in vehicles to distribute power to the wheels. They have different operating principles and are suited to different types of driving conditions. Here's a comparison.
A locking differential will force both tires to rotate at the same speed regardless of the traction each wheel has.
This ensures that even if one wheel is in the air or on a slippery surface, the other wheel can still move the vehicle. It's particularly useful in off-roading and other extreme conditions where traction can be highly variable.
However, a locking differential can make a vehicle difficult to handle on regular roads, especially while turning. This is because wheels on the same axle need to rotate at different speeds while turning, which a locked differential doesn't allow. Some lockers can be manually engaged and disengaged to overcome this limitation.
Limited Slip Differential (LSD)
Limited slip rear differentials allow the wheels on an axle to rotate at different speeds, like an open differential, but it also has a mechanism to limit the speed difference. When it detects that one tire is spinning faster than the other, it redirects more torque to the slower rear tire and axle shafts.
This means that if one wheel loses traction, the LSD will still deliver power to the wheel with traction, helping to maintain the vehicle's momentum. However, it's not as effective as a locking differential in extreme conditions because it can't fully lock the two wheels together.
An LSD uses axial and radial thrust to offer a good balance of performance for both regular and challenging driving conditions. It improves traction and handling over an open differential without the harsh handling characteristics of a locker on regular roads. Plus, it controls the spider gears.
About The Author
I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.Read More About Charles Redding