• A Torsen ("TORque SENsing") limited-slip differential isn't technically a limited slip differential. It's to call it just a Torsen differential or a helical differential. Torsen differentials improve your car's ability to turn. With an open differential, a car will deliver power to the wheel that has the easiest time of it - this means the wheel with the least grip. You might assume this means when one wheel is in mud or sand while the other on pavement, but this also occurs in turns. The inside wheel is always naturally easier to spin. However, when you're turning, it's best to have the force on the outside wheel. The outside wheel has leverage and it will "push" the weight of the car in the direction it's facing. The inside wheel has less grip (because the car tilts and puts its weight on the outside wheel), and can only pull, with far less leverage. This results in drastically reduced high-power or sudden turning capability, especially in front-wheel drive vehicles, though rear-wheel drive suffers from an open differential as well. A normal limited slip would simply activate whenever one wheel is spinning slower than the other. Most differentials of this type are VLSDs - Viscous Limited Slip Differentials. They have two plates, each connected to a wheel, narrowly separated by a thick oil. As one wheel spins faster, one of the plates spins and the heat it generates causes friction, which "grabs" the other plate and forces it to spin at approximately the same speed. VLSDs are very robust and almost maintenance-free, but aren't the best performers (though the difference between even an abused VLSD and an open differential is remarkable.) There are also mechanical ("clutch pack") differentials which use a series of clutches in place of the plates and oil, to force the transmission to distribute torque to the wheels more equally. Clutch packs are great performers, but need to be rebuilt, are somewhat more expensive and their engagement can be quite harsh. Depending on the settings (1-way, 1.5-way, 2-way, as well as the "hardness" of the reaction), the clutch pack may even make the car more difficult to drive. A very hard 2-way can make regular turns you'd coast through be laborious, since both wheels will want to spin at the same speed. It's almost like driving with a welded differential. (in case you haven't realized, the whole point of a differential is to allow different speeds for the wheels, so that turning is possible, since the outside wheel always needs to move more quickly.) A Torsen differential isn't a real limited slip because if you place one wheel on slick ice and the other on dry pavement, the one on ice will still spin itself silly. The torsen is a gear-based differential, the gears are cut in a helical fashion (at angles). When a car turns, the gears press against each other and slide into place, distributing the torque in the best way possible for the turn. This makes it particularly good for front-wheel drive cars, which have a tendency to spin the inside wheel too much and "understeer". A Torsen won't get rid of understeer, but it will make turns much sharper.

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