Limited-slip (posi) rear differentials and locking (locker) differentials are two types of rear differential mechanisms used in vehicles, each with its own characteristics and applications.
Car rear differentials essentially transfer the power from your engine to your wheels via the axle, allowing your vehicle to move. In a posi differential, the unit senses which wheel has the greatest traction, when one tire is slipping or stuck, and sends power to that wheel. Power to the other wheel continues until equal control is returned to both tires. Posi is beneficial when road conditions are wet or muddy. Locking differentials allow both wheels to travel at the same speed, so when traction is lost for one wheel, both wheels will keep spinning regardless of the amount of resistance. They can be added to either the front or rear axle, or even both axles if you are planning on doing some hardcore off-roading.
Here are the main differences between them:
Rear Differentials Function
- Posi (Limited-Slip) Differential: A limited-slip (Posi) differential is designed to allow some differentiation in wheel speeds during cornering while still providing increased traction compared to an open differential. It limits the speed difference between the two wheels, helping to maintain traction on slippery surfaces or during hard acceleration.
- Locker (Locking) Differential: A locker (locking) differential locks both wheels on an axle together, ensuring they rotate at the same speed regardless of traction conditions. This provides maximum traction in off-road situations or when driving on uneven terrain where one wheel may lose grip.
Rear Differentials Operation
- Posi (Limited-Slip) Differential: A limited-slip differential uses clutch packs, gears, or viscous fluids to transfer torque between the two wheels on an axle. When one wheel loses traction, the limited-slip mechanism engages to send power to the wheel with more grip.
- Locker (Locking) Differential: A locking differential physically locks both wheels on an axle together, either automatically or manually. This ensures equal power distribution to both wheels, regardless of traction conditions.
Diagram of a limited slip rear differential
Traction Control
- Posi (Limited-Slip) Differential: Limited-slip differentials provide increased traction compared to open differentials by transferring power to the wheel with more grip. However, they may not provide as much traction as a locker differential in extreme off-road conditions.
- Locker (Locking) Differential: Locker differentials offer maximum traction in challenging off-road situations by locking both wheels together, preventing one wheel from spinning freely and ensuring both wheels receive power.
Driving Characteristics
- Posi (Limited-Slip) Differential: Limited-slip differentials are well-suited for daily driving and performance applications, providing improved traction and stability without sacrificing on-road handling characteristics.
- Locker (Locking) Differential: Locker differentials are primarily used in off-road vehicles and trucks where maximum traction is required in extreme conditions. They may result in more noticeable handling changes and steering resistance on paved surfaces.
Engagement
- Posi (Limited-Slip) Differential: Limited-slip differentials typically engage automatically based on traction conditions, requiring no input from the driver.
- Locker (Locking) Differential: Locker differentials may have automatic or manual engagement modes. Some lockers engage automatically when traction is lost, while others require manual activation by the driver.
Finally
In summary, posi (limited-slip) rear differentials provide increased traction and stability for everyday driving and performance applications, while locker (locking) differentials offer maximum traction in extreme off-road conditions or when driving on challenging terrain. The choice between them depends on the intended use of the vehicle and the driving conditions it will encounter.
