Traction isn’t something that most drivers think about, since under normal weather conditions, at or near posted speed limits, there’s plenty to go around. On the race track, however, the ability to get power to the ground becomes critical.
Enter the limited-slip differential, like the Torsen-branded unit used in the 2013 Scion FR-S (and its cross-brand sibling, the Subaru BRZ). The job of a limited-slip differential is to transfer torque from a wheel that’s lost traction to a wheel that still has traction.
Without getting into too much driving physics, think about what happens as you head into a right hand corner. At turn-in, you transfer weight to the outside (left side) wheel of the car, as you lighten the inside wheel.
Get on the power at the apex of the corner without a limited slip differential, and you’ll likely spin the inside wheel, since it now has less traction than the outside wheel. With a limited slip differential, torque would be distributed from the wheel that’s lost traction to the wheel that still has it.
The benefits of a limited slip differential carry over to street driving as well, since cornering on wet or icy roads can also create a loss of traction. It’s important to note that even the best differential can’t create grip, but it can optimize the traction that’s available to the tires at a given moment.
There’s a bit more to the puzzle than we’ve outlined here, since factors like tire compound and the car’s electronic stability control also come into play, but the net result is this: a limited slip differential will make you faster around a track and safer on the street.