In automotive marketing hubbub and journalistic reviews, you’ll quite often see the term “Limited-Slip Differential” thrown around with great verve. Car companies love to boast about the limited-slip differentials found in their cars. Journalists also love to praise their capabilities. But what is a limited-slip diff and why are they so important? Auto Express shows us why in this new video.

AE is currently running a series of videos, explaining automotive tech in alphabetical order. This latest video is at the letter “L” and the first bit of tech that they explain is the limited-slip diff. The aforementioned tech was developed in the 1930’s and it was invented to limited wheel spin across the driven axle by allowing the output shafts from the diff to turn at different speeds. At the same time, it limits the difference between those speeds.

The limited-slip diff is helpful in almost any application. By varying the torque across a driven axle, it maximized traction and this goes for rear-wheel drive sports cars, off-road SUVs and anything in between. Ever wonder why BMW M cars can do such fantastic burnouts, extremely controllable skids and put their power down so well? Limited-slip differentials.

Nowadays, many car companies use electronically controlled LSDs. These are far more accurate than their viscous-coupling alternatives and can very torque much faster. However, aside from the electronics controlling LSDs, they work almost exaclty the same as they did back in the ’30s. BMW’s current electronic limited-slip diff in its proper BMW M cars works brilliantly and is one of the best parts about them. Also, the limited-slip diff option from BMW’s M Performance Parts division can transform the way cars like the BMW 340i and M240i perform.

This video is a bit nerdy but if you’re a car nerd, as I am, it’s worth watching.