What Is a Car LSD?

The differential is an important part of any vehicle. There are several different types of differentials, each with its strengths and weaknesses. Some vehicles have a limited-slip differential, which has the unfortunate acronym of LSD. So what is a limited-slip differential, exactly? And how is it different from other differentials?

What Is a Car LSD?

The limited-slip differential is a type of differential. Differentials are gear trains that allow the wheels on each end of the drive axle to spin at different speeds whenever you make a turn.

Depending on its design, the LSD uses one of several ways to lock itself. Some limited-slip differentials rely on a complex gear train with helical gears.

Second, the LSD can use clutch packs. When one of the wheels starts to slip, the differential binds its clutch plates together.

Last but not least, the LSD can use a viscous lubricant fluid. The fluid can increase friction, making it much harder for a wheel to spin freely.

General Motors refers to its limited-slip differential designs as Positraction. The GM brand name became recognizable enough that many people call LSDs by that name.

Differentials are complex systems with myriad moving parts. Whether it’s an LSD or another type, a differential requires regular maintenance and proper service throughout its lifetime.

What Does the Car LSD Do?

As its name implies, the limited-slip differential reduces the risk of tire slippage. It prevents the difference in the wheel speeds from growing too great.

The limited-slip differential can compensate for tire slippage by sending torque to both wheels. It also prevents one wheel’s rotation speed from exceeding that of the other wheel.

To better understand the capabilities of the limited-slip differential, let’s look at differentials as a whole and compare the different types.

What Is A Differential?

Also called diffs, differentials have three drive shafts. One input shaft connects to the transmission while two output shafts lead to the drive wheels.

The differential divides engine torque transmitted by its input shaft. It then sends the split force into its output shafts.

When the torque rotates the shafts, the attached wheels spin as well. The rotating wheels propel your vehicle backward or forward, depending on the direction of the rotation.

Differentials come in several different types. Here are the most common ones:

Open Differential

Open differentials are the most common type. They set the standard for differentials, ensuring that the wheels and tires on opposite ends of a drive axle can spin at different speeds.

An open differential has a notable drawback. When a tire slips and rotates too fast, it reduces the torque in the wheel on the opposite side of the drive axle. If the tire with better traction can’t produce enough torque to compensate for the slipping tire, the vehicle might become more difficult to control and steer.

Most vehicles have a traction control system (TCS) that works with the open differential to maintain traction. The TCS engages the brakes of the slipping wheel, producing reaction torque that compensates for the torque reduction.

Crossovers, economy cars, family sedans, and minivans usually feature open differentials. These vehicles have undemanding performance and always stay on the roads.

Locking Differential

Next up is the locking differential, which improves on the open differential by fixing the latter’s main problem. As its name indicates, this diff can lock itself, forcing the wheels on either side of the drive axle to rotate at the same speed.

A locked differential keeps torque flowing to the wheel with greater traction. It prevents torque reduction while driving over loose or slippery substances like mud, sand, and snow.

Despite overcoming the main issue of the open differential, the locking differential isn’t perfect. For one thing, the driver must lock it. Otherwise, the unengaged differential acts like an open diff.

Furthermore, the locking differential’s strongest advantage can turn into a drawback if the vehicle goes over high-grip road surfaces. If you drive over the dry pavement with the diff locked, turning the vehicle becomes harder. You might also grenade the driveline.

Examples of vehicles that use a locking differential are Jeep Wranglers, the Mercedes-Benz G-class, and Ram 2500 Power Wagon. Many full-size trucks offer the option to upgrade to a locking differential.

Limited-Slip Differential

The LSD combines the best traits of open and locking differentials. In typical driving scenarios, it acts like an open differential. But when one of the wheels starts slipping, the limited-slip differential automatically locks itself.

Once the wheels return to their usual rotation, the LSD operates like an open differential again. It doesn’t require you to engage or disengage it manually.

Not all limited-slip differentials deliver the same performance. Mechanical limited-slip diffs react to wheel slippage. They won’t lock up preemptively, which might cause problems in some situations.

Torque-Vectoring Differential

Last but not least is the torque-vectoring differential. The most advanced option, it uses an array of sensors to gather readings on variables like the steering system.

The torque-vectoring differential system can assign the right amount of torque to each wheel as needed. It helps generate maximum traction for the best driving performance.

What Vehicles Usually Have an LSD?

There are two groups of vehicles that benefit from having a limited-slip differential. And they couldn’t be more different from each other.

You see, LSDs are often seen in performance vehicles like sports cars that stick to good roads. At the same time, SUVs and trucks that go off road will also benefit from having a limited-slip differential.

On performance vehicles, the limited-slip differential improves handling, especially while making turns. Race cars often corner at high speeds, causing the wheel on the outside of the turn to spin faster than the one on the inside. The LSD stops the outside wheels and tires from spinning too fast, helping to retain control and keep you safe.

Off-road vehicles also benefit from the LSD’s capabilities. Pickup trucks and SUVs need all the traction they can get on slippery road surfaces and loose material. The limited-slip diff can help keep their wheels from spinning out of control.

Examples of vehicles equipped with an LSD include the Nissan 3702 with Sport package, the Mazda MX-5 Miata, and the Scion FR-S/Subaru BRZ.

Even if you don’t own a race car or an off-road vehicle, the car LSD will make driving easier and safer, giving you the peace of mind you deserve.