One tire fire: why limited slip differentials are a performance car must-have
It’s all about putting the power down on corner exit
Most performance cars nowadays are sold with an open differential, even if the solution somewhat hampers their cornering capability. Sure, using an open differential makes the car easier to control (especially if it’s rear-wheel drive) and more efficient, but for performance driving it’s not really what you want.
Differentials have the task of splitting the power from the engine and sending it to each of the powered wheels, but if one drives a car with an open diff fast, it essentially squanders most of the power on corner exit by sending it to the path of least resistance - the inside wheel with the least traction. This results in said wheel spinning the power away, making a lot of noise and smoke, but not really pushing the car forward.
On top of this, since open diffs split power exactly 50/50, one tire loses traction and this limits how much power is sent to the tire that is still gripping. It’s all very safe, but it essentially limits the fun you can have in certain vehicles.
This is where limited-slip differentials come in as they automatically lock in these situations, thus distributing power evenly and helping a car shoot out of corners. It results in the inside tire not lighting up, but it also requires a more alert driver to counteract any waywardness that may occur when both wheels receive power - if the car is rear-driven, oversteer may occur, while if it’s front-driven, it may violently tug at the wheel and understeer; it also accelerates tire wear and makes the car use more fuel.
Many different styles of differential that essentially try to do the same thing (improve traction) are available, and they vary in price, complexity and efficiency. The most basic of these is a fully locked or welded differential that basically means both wheels turn at the same speed all the time, even when you’re just cruising around and don’t want brutal corner exit.
This style of differential can’t be found on any modern car and you usually have to make this modification yourself if you plan on racing your car or taking it drifting. Some vehicles do have diffs which you can manually lock, but they’re usually not the kind of vehicles you want to drive fast on-road - but then again, locked differentials work wonders off-road where they are actually essential to keep making progress in some situations.
Another better all-round solution are viscous limited slip differentials (VLSD) which rely on fluid pressure inside to actuate perforated disks which in turn are connected to the output shafts. This could be seen as a best of both worlds solution, as it allows for different wheel speeds, but they lack the efficiency of mechanical locking differentials, and over time they start to lose their locking ability, slowly turning into an open type differential through wear.
Mechanical locking diffs are of several types but their main advantage is that they can lock quicker than VLSD through the use of clutch packs, even if this may cause jerkiness which the latter lacks. But for performance driving they are one of the better solutions as they can and do send power to the wheel with most grip. The best one to have is what is known as an ELSD which uses computers to control when to lock, thus providing better and more consistent real world performance.
Torsen (from torque sensing) is another type of differential preferred by sports car manufacturers for its low maintenance but good performance. It is said to be the best for the road because under normal driving conditions it works as a fully-open diff, but once one tire starts to lose grip (and spins at a different speed to the other driven wheel) power from it is transferred to the one that’s still hooked up.