A guide to the types of differentials and torque vectoring.
Before we get into it, let's start with the basics of the car differential; whether it be gas, diesel, hybrid, or electric. A car's power source delivers a certain amount of power to the wheels via a driveshaft, or a front differential transaxle in the case of a front-wheel-drive car. The power produced by this driveshaft needs to be split to drive the two wheels. That's why differentials exist: to split the power between the wheels while allowing them to travel at different speeds
So, what is a differential? A differential is a crucial component in the front or rear axle assembly, and it allows you to turn without drivetrain windup. The engine sends power via the transmission to a driveshaft that is connected to the rear differential, where the power is split via a set of gears. These gears can increase or decrease the revolutions per minute of each wheel.
Why? Think of a car doing a basic U-turn to the left and what the front and rear wheels are doing while this is happening. The left wheels, or in this case, the inside wheels, have a much shorter distance to travel than the outer right wheels. A differential's gearing allows this to happen. It will enable the inner tire to travel at less rpm while the outer tire is spinning at a higher rpm.
There isn't just one gear in a car differential or diff, but a few different parts. The differential in a car consists of:
Here is a summary of how a differential works: The flange is essentially the coupling between the driveshaft coming from the engine and the differential. It connects to the pinion gear, which turns the drive gear. This is connected to three spider gears, which connect to two more side gears, which connect to the half shafts. These are the basic components of an open differential, which is the most commonly used in cars. When a vehicle is moving in a straight line, only the drive gear and half shafts are moving. As soon as the car turns, the spider gears take over and allow the half shafts to move at different speeds.
For decades, there were three types of differentials, namely, the open, limited-slip, and locked differential. With advancements in drivetrain technology, a few additional examples have been added to the list. In some electric vehicles, the electric motor is housed within the wheel, completely removing the need for a traditional car differential. Here's a list of the most common differentials in production today.
On a front-wheel-drive car, the differential is integrated into the gearbox housing and uses the same lubrication fluid. In rear-wheel-drive cars, the differential is obviously at the back and is therefore often overlooked when a car goes in for a service. It depends entirely on how you use your car, but the average mileage for fluid replacement is between 30,000 to 50,000 miles.
The answer is quite simply general abuse. The limited-slip differential in your rear-wheel-drive car was put there to provide additional grip and some slidey action, but that doesn't mean you should powerslide around every corner. Not only is it dangerous, but it tends to lead to overheating. On the flip side, you need to give the differential some time to warm up before giving it the beans. The first-generation Mercedes-AMG CLK Black famously came with a warning letter telling the driver to do this. When it comes to 4x4s, differentials are usually damaged by sharp rocks. Investing in proper underbody protection before off-roading is an absolute must-have off-road modification.
A damaged differential is easy to diagnose. Because it's such a vital part of the car, you will definitely notice. First, the driveshaft will vibrate, you'll hear the sound of gears grinding, and a whining noise coming from the driven wheels. A quick check underneath the diff should reveal whether you have a leaking problem. If you know your car well enough, you'll notice a change in the handling. Turning into a corner will be harder, and in a worst-case scenario the differential will lock up. Uneven wear on the tires is also a sign of a differential starting to fail. Check out our guide on common car problems for more troubleshooting help.
If it's just a basic repair like new fluids and seals, the bill will be between $200 to $400. Once the gears are damaged, things get pricey. For a full set of replacement gears, you're looking at a minimum of $1,500. For the really advanced differentials, a full replacement can cost as much as $4,000.
Yes. Most electric vehicles use either a single- or dual-motor setup. The torque still needs to be distributed between the wheels, so a differential is required. Tesla uses open differentials on its cars, for example. On some next-generation cars, the electric motor will form part of the wheels assembly, which means a car can have either front, rear, or all-wheel-drive without any mechanical linkages.
A limited-slip differential won't get you arrested, but an LSD pill most certainly will. Also, don't drop acid before drifting. Actually, the police aren't big fans of drifting in public spaces in general, so keep limited-slip diff use only for the track.