Limited-Slip Differential: How Does It Work?
Four-wheel and all-wheel drive systems help improve a vehicle’s grip in various conditions, but another device called “limited-slip differential” also serves that purpose in many performance cars, including the Mazda MX-5, the Porsche 911 and the Honda Civic Type R, but in SUVs that are focused on off-road driving too.
Essentially, a limited-slip differential reduces the speed difference between the driving wheels when one of them loses its grip or slips, hence the name. It works permanently and requires no input from the driver.
With a traditional differential, when there’s a loss of traction, most of the torque goes to the wheel that has the least resistance—in other words, the one that slips. The limited-slip differential will rather balance the torque gap between the two half-shafts.
How? Via a rotation inside the differential, so that one of the drive shafts spins faster than the other. The friction torque allows to slow down the faster wheel and give more power to the slower wheel. This facilitates path control and reduces the risk of swerving.
Car manufacturers program these differentials to operate when a certain slipping threshold is reached, which is monitored by a sensor.
By the way, limited-slip differentials can be controlled electronically while still being of a mechanical nature, but there are also fully electronic ones. These use the brakes to reduce the torque transferred to a wheel when the sensor sees that it spins too fast. In this case however, the power is partly lost in the braking instead of being transferred to another wheel. This system is cheaper, but doesn’t allow the same efficiency as a mechanical differential.
And remember this: if your vehicle is equipped with an electronic limited-slip differential and you have a flat tire, don’t use a spare wheel of a different size. If you do, the system will be deactivated, or its action will be reduced, to avoid overheating and other damage. It’s recommended to reinstall the original wheel with a new or repaired tire as soon as possible.
