Limited Slip Differential: The Secret of the famous LSD

Differentials are a crucial component of any vehicle’s drivetrain, playing a pivotal role in optimizing performance and handling. Among the various differential types, the Limited Slip Differential (LSD) stands out as a remarkable engineering innovation that has revolutionized the automotive industry.

In this article, we will delve into the world of Limited Slip Differentials, exploring their definition, purpose, and the advantages they offer over traditional open differentials.

limited slip differential

What is a limited slip differential (LSD)

A differential is a component that allows the drive wheels (the ones that receive power from the engine) on the same axle to rotate at different speeds while driving around curves or corners.

In a limited slip differential, there is a mechanism that limits the independence of rotational speed between the two wheels on the same axle. It distributes power more evenly to both wheels than a normal or open differential would, providing better traction and stability.

When one wheel loses traction, some of the engine’s power is transferred to the wheel with a better grip, which helps the vehicle maintain control in slippery or uneven road conditions.

Limited slip differentials come in various designs, including clutch-type LSDs, gear-type LSDs, and viscous LSDs, among others. Each design has its characteristics, advantages, and disadvantages, but the primary goal is to enhance the car’s performance and handling, especially in challenging driving situations.

How Limited slip Differential Differs from Open Differentials

The key distinction between an LSD and an open differential lies in their ability to distribute torque. While an open differential prioritizes ease of turning and maneuverability, it lacks the capacity to manage unequal wheel traction effectively.

In contrast, an LSD employs a variety of mechanical and technological means to limit the speed difference between the two wheels. This restriction ensures that power is transmitted to the wheel with more traction, enabling the vehicle to maintain stability and control.

What is an Open Differential and What Does It Do?

Before going to deep it is important that everyone has the same understanding of what a normal or open differential is, as it is the base to an LSD.

The Basic Function of Open Differential

The primary function of an open differential is to distribute power evenly between the two wheels on the same axle. When the vehicle is moving in a straight line, both wheels receive an equal amount of torque, resulting in balanced rotation and smooth operation.

During a turn, however, the wheels on the outside of the curve must travel a greater distance than the wheels on the inside. This difference in distance would lead to significant binding and resistance if both wheels were forced to rotate at the same speed.

The open differential, with its ability to allow different rotational speeds for each wheel, prevents this binding and allows the vehicle to navigate turns with ease.

If you are interested in knowing exactly how a differential works we recommend you check out the following article were we go in depth on the internals of an open differential: Welded Differential: In The World Of Differentials

Limitations and Traction Issues

While the open differential’s ability to permit independent wheel rotation makes it ideal for regular driving and turning, it comes with certain limitations, particularly in terms of traction.

When one wheel loses grip on a slippery or low-traction surface, the open differential will redirect all the from the engine power to that wheel with the least resistance. As a consequence, the wheel with traction, even if it has excellent grip, will receives a minimal amount of torque, leading to potential wheel spin.

This lack of torque management can be problematic in challenging driving conditions, such as snowy or muddy roads, as well as off-road terrains.

In these situations, the open differential may struggle to deliver the necessary power to the wheel with better traction, resulting in reduced stability and control. This is when a limited slip differential can be very handy.

What are the different type of limited slip differentials

Limited Slip Differentials (LSDs) come in various configurations, each tailored to meet specific driving needs and conditions. These different types of LSDs employ unique mechanisms to distribute torque and enhance traction, making them indispensable in diverse driving scenarios.

Different Activation types

There is three main way the different mechanism of a LSD will activate or react to properly distribute the power of your engine:

Torque-Sensitive Differentials

Torque-sensitive LSDs, also known as torque-biasing or torque-sensing LSDs, rely on mechanical or hydraulic systems to detect the difference in torque between the two wheels.

When one wheel experiences slippage or loses traction, these LSDs react by transferring more torque to the wheel with better grip. This characteristic ensures improved traction on slippery surfaces and during cornering, making torque-sensitive LSDs a popular choice for performance-oriented vehicles and everyday driving.

  • Torque Sensitivity (HLSD): Highly limited slip differentials (HLSDs) take torque sensitivity to the next level, offering even greater bias towards the wheel with more traction.

Speed-Sensitive Differentials

Speed-sensitive LSDs, as the name suggests, take into account the rotational speed of the wheels to determine torque distribution.

They use sensors to monitor wheel speed and adjust torque allocation accordingly. These LSDs are effective in providing seamless transitions between different driving conditions, ensuring stability during turns and maintaining traction on varying road surfaces.

Fixed Value LSD

Fixed value LSDs maintain a consistent torque distribution regardless of driving conditions or wheel slip. These LSDs are often set to distribute torque in a predetermined ratio, offering a balance between stability and maneuverability.

While fixed value LSDs may not provide the adaptability of some other types, they are still beneficial in improving traction during moderate driving scenarios.

The different ways: 1-Way, 2-Way 1.5-Way LSD

These designations refer to the number of ways the LSD operates.

  • 1-Way: A 1-way LSD only engages during acceleration, providing enhanced grip when power is applied.
  • 2-Way: A 2-way LSD offers limited slip functionality during both acceleration and deceleration, ensuring consistent traction under various driving conditions.
  • 1.5-Way: The 1.5-way LSD is a hybrid of both, providing limited slip during acceleration and moderate slip during deceleration, striking a balance between the two.

Different limited slip diffeential mechanism

Clutch, Cone-type, or Plate LSD

In a Clutch, Cone-type, or Plate LSD, the differential’s main components include friction discs or plates, which are situated between the differential housing and the side gears connected to the wheels. These plates are often lined with a friction material, and their function is to control the distribution of torque between the two wheels on the same axle.

When both wheels have equal traction, the friction plates do not engage, allowing the differential to function like an open differential, permitting the wheels to rotate at different speeds as needed during turns.

However, when one wheel experiences reduced traction (e.g., due to slippery or uneven surfaces), the friction plates are pressed together, creating additional friction. This increased friction helps transfer more torque to the wheel with better traction, reducing the power sent to the wheel that’s slipping.

The Clutch, Cone-type, or Plate LSD design provides improved traction and stability in various driving conditions. It is commonly used in performance-oriented vehicles, sports cars, and some off-road vehicles where better handling and cornering capabilities are desired.

Gear limited slip differential

In a gear LSD, the main components include a set of worm and spur gears. These gears are designed in such a way that they can be engaged to varying degrees, depending on the rotational speed difference between the two wheels. When both wheels have similar rotational speeds, the gears do not engage, and the differential functions like an open differential, allowing the wheels to rotate at different speeds during turns.

However, when one wheel loses traction and starts spinning faster than the other wheel, the gears react to this speed difference and engage, creating a locking effect. This locking action reduces the speed difference between the wheels and helps transfer more torque to the wheel with better traction, improving overall traction and stability.

Gear LSDs are known for their robustness and reliability, making them suitable for high-performance applications and off-road vehicles. They tend to require less maintenance compared to clutch-type LSDs since they do not use friction materials that may wear out over time.

Viscous lSD

A Viscous LSD (Limited Slip Differential) is a type of limited slip differential that relies on hydrodynamic friction from fluids with high viscosity, typically using silicone-based oils. In this design, a cylindrical chamber of fluid filled with a stack of perforated discs rotates with the normal motion of the output shafts. Half of the discs are connected to the inner surface of the chamber, and the other half to the outer surface, alternating inner/outer in the stack. The inside surface of the chamber is coupled to one of the driveshafts, and the outside is coupled to the differential carrier.

Differential motion forces the interleaved discs to move through the fluid against each other. When there is a speed difference between the wheels, the fluid experiences friction, and the discs tend to lock together, transferring more torque to the wheel with better traction. This limited slip action provides improved traction and stability.

Viscous LSDs offer a smoother and more gradual engagement compared to mechanical LSDs, making them easier to handle for the average driver. However, they are less efficient and may “lose” some power due to the energy dissipated as heat in the silicone-based fluid during operation.

  • Generator Pump Style: Another style of Viscous LSD uses a gerotor pump to hydraulically compress a clutch, transferring torque to the wheel that is rotating slower.

Electronic LSD

The basic structure of an electronic LSD includes a planetary or bevel gear set similar to that of an open differential, and a clutch pack similar to those found in torque-sensitive differentials. The clutch pack is responsible for transferring torque between the wheels, allowing limited slip action when there is a speed difference between them.

In the electronic LSD, the clamping force on the clutch pack is externally controlled by a computer or other electronic controller. This external control allows for precise management of the differential’s limiting torque (Trq d), making it possible to integrate the differential’s behavior into a total chassis management system. The electronic control enables adjustments to be made in real-time, depending on driving conditions, road surfaces, and the driver’s inputs.

Brake Based LSD

Another type of electronic LSD is the brake-based system, which uses various chassis sensors, such as speed sensors, ABS sensors, accelerometers, and microcomputers, to monitor wheel slip and vehicle motion.

When the system detects wheel slip, it applies the brakes to the slipping wheel, effectively transferring torque to the wheel with better traction. This type of system does not inherently send more torque to the slower wheel, but it effectively controls wheel slip and stability.

limited slip differential vs Welded Differential

When it comes to optimizing a vehicle’s traction and handling characteristics, two differential options often enter the discussion: Limited Slip Differentials (LSDs) and Welded Differentials. Both choices offer distinct advantages and drawbacks, catering to specific driving preferences and conditions.

Here’s the difference:

Limited slip differential

A Limited Slip Differential is a sophisticated mechanism designed to distribute torque more effectively between the wheels, offering improved traction and stability. LSDs provide a balanced compromise between stability during cornering and smooth turning, making them ideal for various driving scenarios.

They excel in enhancing traction on slippery or uneven surfaces, ensuring optimal performance on the track, off-road adventures, and everyday commuting.

Welded Diff

A Welded Differential, on the other hand, involves permanently locking the two wheels on an axle together, essentially making them behave as a single unit. This modification eliminates the differential’s ability to allow independent wheel rotation, ensuring that both wheels receive the same amount of torque at all times.

This mod is commonly done purely because it is a very simple and very cheap modification that can turn almost any car into a drift missile (on a budget). However, the welded diff creates complication when it comes to normal driving unlike the LSD.

If you want to know more about welded differential and how to weld yours, check out the following article: Welded Differential: In The World Of Differentials

Benefits and drawbacks of a Limited slip differential

Pros

  • Improved Traction and Stability: One of the primary advantages of LSDs is their ability to maximize traction. By actively transferring torque to the wheel with better grip, LSDs minimize wheel spin and ensure that power is efficiently utilized. This enhanced traction is especially valuable on slippery surfaces, uneven terrains, and during sharp turns, where maintaining stability and control is essential for safe and enjoyable driving.
  • Enhanced Handling and Cornering: LSDs play a pivotal role in improving a vehicle’s handling and cornering capabilities. By minimizing the speed difference between the wheels during turns, LSDs help maintain balanced power delivery to each wheel.
  • Better Performance in Various Driving Conditions: Whether it’s navigating through adverse weather conditions, tackling off-road terrains, or engaging in spirited driving on the track, LSDs prove invaluable in a wide range of driving scenarios. Their ability to optimize torque distribution ensures that vehicles can adapt to different surfaces and maintain traction, even in challenging situations.
  • Impact on Tire Wear and Fuel Efficiency: By minimizing wheel spin and unnecessary tire scrubbing, LSDs help reduce uneven tire wear, extending the lifespan of the tires.

Cons

Increased and Cost: LSDs are more intricate in design than open differentials, involving additional mechanical components and engineering. As a result, they are generally more expensive to manufacture and install in vehicles. This cost consideration can be a factor for budget-conscious drivers.

Different Driving Characteristics: LSDs may exhibit slightly different driving characteristics compared to open differentials, especially during low-speed maneuvers. While LSDs optimize traction and stability, some drivers might notice subtle differences in how the vehicle behaves.

Maintenance Requirements: LSDs require periodic maintenance, including fluid changes and inspection, to ensure proper operation.

Compatibility with Electronic Systems: In modern vehicles equipped with electronic stability control (ESC) and other advanced driver-assistance systems, certain types of LSDs might interact differently with these electronic systems. Ensuring compatibility and proper integration is crucial to maintain overall vehicle safety and performance.

Limited slip Differential in Different Driving Scenarios

Limited Slip Differentials (LSDs) showcase their remarkable versatility and performance benefits across a wide range of driving scenarios. Whether on the racetrack, navigating challenging off-road terrains, or simply tackling everyday driving challenges, LSDs play a pivotal role in enhancing vehicle dynamics and driver experience. Let’s explore how LSDs excel in various driving contexts.

LSD in Motorsports

LSDs have a long-standing presence in the world of motorsports, where precision, traction, and control are paramount. In high-speed racing events, such as circuit racing and rallying, LSDs deliver improved acceleration out of corners, reduced wheel spin, and enhanced stability during aggressive maneuvers.

Drivers can confidently push the limits of their vehicles, knowing that LSDs optimize power delivery and maintain grip on tight turns, hairpin bends, and varying road surfaces.

LSD in Off-Roading

Off-road driving demands traction, control, and the ability to navigate challenging terrain. LSDs shine in these conditions by ensuring that power is efficiently distributed to the wheels with traction.

This means better grip on loose soil, rocks, sand, and other uneven surfaces, enabling off-road enthusiasts to conquer obstacles with confidence.

LSDs improved traction, reduce the likelihood of getting stuck in challenging off-road conditions. They also enhance stability on steep inclines and declines, making hill climbs and descents safer and more manageable.

LSD in daily Driving

In daily commuting and urban driving, LSDs provide tangible benefits that enhance safety, stability, and overall driving experience. LSDs excel in adverse weather conditions, such as rain or snow, by reducing wheel spin and improving grip on slippery roads.

Why use a limited slip differential (LSD) for drifting

Using a Limited Slip Differential (LSD) for drifting ensures that both wheels always receive at least some torque all of the time. The “limited slip” feature means that there is still some difference in speed (or slip) allowed between the two wheels because they need to travel different distances in a turn.

However, it’s not unlimited as in an open differential, where one wheel could spin freely without transferring power to the other wheel.

When a driver in a car equipped with a limited slip differential attempts to initiate a drift, the first wheel will break traction, and the limited slip diff will continue sending power to the second wheel. This allows the second wheel to also break traction, initiating a slide.

The continuous torque distribution to both wheels helps maintain better control during the drift, allowing for smoother and more controlled oversteer maneuvers.

In essence, the LSD’s ability to transfer power to both wheels, even during slides, ensures that the car can maintain stability and predictable behavior during drifting.

It provides improved traction, smoother transitions, and better line control, making it a valuable component for drifters to achieve and maintain controlled drifts.

The most commonly used type of LSD amongst drifters is the mechanical, 2-way clutch type.

conclusion

In conclusion, limited Slip Differentials (LSDs) are a revolutionary engineering innovation in the automotive industry, offering better traction and stability by limiting rotational speed between two wheels on the same axle.

These differentials distribute power more evenly, ensuring better grip receives more torque when the other wheel loses traction. LSDs come in various configurations, including torque-sensitive, speed-sensitive, and fixed value models, catering to diverse driving needs.

They have proven versatile in motorsports, off-roading, and daily driving, improving acceleration, stability, and safety in various driving scenarios.