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February 6, 2024

Let's Geek Out On Mazda's Asymmetric Limited Slip Differential

The updated fourth-generation Mazda MX-5, due sometime this year, features two new technologies both honed from the track: DSC-Track and Asymmetric Limited Slip Differential. We’ve tackled in length what DSC-Track does, so now we take a closer look at what Asymmetrical LSD does.

During cornering, the outer wheel travels more distance compared to the inner wheel. If a car wasn’t equipped with a differential, it would either go forward in a straight line or cause the outer wheel to skip over the surface. In the worst cases, it would snap the drive shaft.

To prevent that, carmakers have come up with an open differential. Basically, this transfers the motions of the driveshaft through a series of interlocking gears which allows the wheels on either side to rotate at different speeds.

During daily driving, this is enough. However, the problem with an open differential is that when torque is transferred to the axle, it takes the path of least resistance. On a racetrack, for example, the outer wheel experiences much greater force (making it more difficult to turn) compared to the inner wheel. With the inner wheel being the path of least resistance, it will send most of the available power to that wheel causing the car to struggle for traction or grip.

Enter the Limited Slip Differential or LSD. As its name suggests, it limits the torque difference between the driven wheels thanks to a clutch pack that allows a certain amount of slip between each side of the axle. This prevents traction loss and optimizes grip.

When it comes to Mazda, they’ve had a long history of equipping their vehicles with LSD. The first-generation RX-7 was the first Japanese passenger vehicle to be equipped with it. Since then, they’ve redeveloped it into the “Super LSD” which uses a simple, lightweight, yet durable mechanism with a conical clutch. It was then used in the second-generation MX-5, the RX-8, the third-generation MX-5, and the fourth-generation MX-5.

Now, with the help of GKN Driveline Japan Co., Ltd. (formerly known as Tochigi Fuji Sangyo Co., Ltd.), they’ve developed Asymmetric LSD which they’ve equipped in the 2025 MX-5.

A development 20 years in the making, Asymmetric LSD removes one of the most notable limitations of typical LSD systems which was using the same differential characteristics for both acceleration and deceleration. If the amount of slip is the same during acceleration and deceleration, it might make a vehicle more difficult to turn, especially in narrow confines. It also produces much more driveline noise.

The Asymmetric LSD uses the same conical clutch setup but adds a new cam mechanism allowing for different inputs between acceleration and braking. Strengthening the slip limiting force during braking, for instance, enhances stability when decelerating into a turn, which is where reduced rear wheel ground load causes vehicle instability.

Mazda is quick to point out that the Asymmetric LSD may not result in faster lap times. Instead, it’s all about feel. Their factory test engineers, which drove the MX-5 equipped with the Asymmetric LSD on the Nürburgring for evaluation noted the difference. This subjective difference is what makes the MX-5 different from other sportscars in the market, and one that’s made it a true icon, especially to those who love driving.

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