Put one driven tire on ice and the other on dry pavement, and an ordinary differential can leave the car going nowhere. The dry tire can only take as much torque as the icy one can hold. A limited-slip differential exists to break that rule.
The short answer
A differential lets the two driven wheels turn at different speeds. In a turn, the inside wheel turns slower than the outside one. An ordinary, or open, differential allows that, but it always sends equal torque to both wheels.
A limited-slip differential (LSD) still lets the wheels turn at different speeds, but it limits how far apart they can get. That lets the wheel with grip take more torque than the one that is slipping.
What goes wrong with an open differential?
Wikipedia's example: if the icy tire starts to spin at 50 lb-ft, the tire with traction cannot get more than 50 lb-ft either, which is far less than it takes to move the car. One wheel spins, and the other can sit still.
How does a limited-slip differential work?
Every LSD adds something inside that resists the two wheels turning at different speeds. Eaton, a maker, defines it as a differential that partially reduces, but does not totally eliminate, individual wheel spin. How much torque it can shift toward the tire with grip is called its bias.
Three common ways to build that resistance:
| Type | What resists the slip | Found in |
|---|---|---|
| Clutch | Clutches that clamp to tie the two wheels together | Eaton Posi, Mazda MX-5 Miata Club (2024) |
| Helical gear | Gears that press into the case, making friction that rises with torque | Torsen in the Mustang Boss 302 and Camaro Z/28 |
| Electronic | A computer-controlled hydraulic clutch | Camaro ZL1 (2017-2019), 6.2L V8 Corvette (2015-2019) |
Clutches. Eaton's Posi puts carbon clutch packs, preloaded by springs, behind each side gear. When one wheel slips, the clamping load rises and power goes to the other wheel. Mazda's conical-clutch LSD uses a cam with different ramp angles for acceleration and deceleration: it locks harder under engine braking for stability into a corner, and less on the throttle to cut understeer.
Helical gears. In a Torsen, torque pushes the gears against the case. More torque means more friction and more resistance to wheel spin.
Electronic. GM's system reads speed, throttle, steering angle and yaw rate, then sets a hydraulic clutch anywhere between open and locked. It can go from one to the other in 0.15 seconds or less.
What is torque bias ratio?
It is the number that rates a Torsen. At 2:1, the wheel with better grip can get up to twice the torque of the other, and the diff resists one-wheel spin until one tire has more than twice the traction of the other. Torsen's Type-2 units run about 2:1 to 2.5:1. Its more aggressive T-2R runs 3:1 to 4:1.
GM shows the same idea as a percentage on the dash: 0 % is an open diff, 100 % is locked. Driving straight, its eLSD holds around 10 to 15 % for stability. Accelerating hard on a track, it climbs to around 40 to 50 %.
What's the catch?
An LSD cannot lock fully. Eaton warns that if one wheel has no traction at all, there may not be enough torque at the other wheel to move the car.
It also cares about tires. Mazda's MX-5 manual says mixed tire sizes or types, or underinflated tires, make the left and right wheels turn differently, put a constant load on the LSD and cause a malfunction.
On the street
If someone says a car has "posi," they mean an LSD. Positraction was GM's brand name for Chevrolets, and it became the generic US word for any limited-slip differential.
Muscle cars on live rear axles, without an LSD, spun one tire so often it got a name: "one wheel peel." And Torsen units are not just for sports cars; they run in everything from the military HMMWV to Audi Quattro sedans.
FAQ
Is a limited-slip differential worth it on a daily driver?
Torsen itself steers daily drivers to its milder Type-2, especially for winter use, and autocrossers to the more aggressive T-2R.
Does a limited-slip differential help in snow?
Yes. GM describes pulling away with one wheel on ice and one on dry pavement: the eLSD moves torque to the wheel with more traction.
Do you need one to drift?
Wikipedia notes that mechanical limited-slip differentials are considered essential for a proper drift.
Sources
- Limited-slip differential (Wikipedia), read 2026-10-24
- What is a limited slip differential? (Eaton), read 2026-10-24
- Posi limited-slip differential (Eaton), read 2026-10-24
- How it works (Torsen), read 2026-10-24
- FAQ (Torsen), read 2026-10-24
- About Torsen (Torsen), read 2026-10-24
- Electronic Limited Slip Differential DIC Screens (GM TechLink), read 2026-10-24
- 2024 Mazda MX-5 Miata: Pricing and Packaging (Mazda USA Newsroom), read 2026-10-24
- 2019 MX-5 owner's manual: tire rotation (Mazda USA), read 2026-10-24