LSD Upgrade Kits

A limited-slip differential (LSD) stops the unloaded inside wheel spinning away the engine's power out of a corner. Choosing one comes down to how it acts on and off the throttle, how much it locks before any torque goes through it, and how it is built.

1-way, 1.5-way or 2-way

• 1-way locks under acceleration and behaves as an open differential off the throttle. Suits front-drive cars, the front axle of four-wheel drives, and rear-drive cars set up for time attack.
• 1.5-way locks under acceleration and partly under deceleration, with less lift-off understeer than a 2-way. The usual choice for rear-drive cars and the rear axle of four-wheel drives.
• 2-way locks with the same force on and off the throttle, which holds a rear-drive car steady through big slides: the drift choice.

Initial torque

Initial torque is the preload that couples the two wheels before any drive torque is applied; Japanese makers quote it in kgf·m. Lower initial torque means less drag and a lighter feel in tight turns and car parks; higher initial torque makes the diff lock harder from the start. Cusco's two designs for the GR Yaris rear axle show the spread: about 2 to 4 kgf·m for the spring-loaded Type RS against 8 to 10 kgf·m for the cone-spring Type MZ.

Initial torque falls as the clutch plates wear, and is set again when the diff is serviced or its pressure rings are changed. Cusco sells alternative pressure rings that change the cam angle, so one unit can be moved between settings.

Clutch-type or geared

Most LSDs here, from Cusco, OS Giken, KAAZ and Nismo among others, are clutch-type: friction plates pressed together by cams and springs, with the 1-way, 1.5-way or 2-way character set by the cam. Geared helical units, such as R's Racing Service's helical LSD, use gears pressed against the housing instead of plates, and their locking rises with the torque going through them.

A clutch-type LSD is a serviceable part: keep LSD repair parts and the right LSD gear oil in mind, and on a hard-driven car, a transmission and LSD cooler. An LSD puts more torque to the ground, so check that the clutch can hold it too. The drivetrain guide covers the rest.