Audi Quattro vs BMW xDrive vs Mercedes 4MATIC – Engineering Explained

Audi's Quattro, BMW's xDrive, Mercedes' 4Matic. It's not just all-wheel drive. It's a battle of brand DNA. This video is not a spec sheet comparison. This is a step-by-step working of each system, and this is going to be technically deep. All-wheel drive means all four wheels receive torque. But how, when, and how much? That's what sets each system apart. We'll start with Audi's legendary all-wheel drive system, Quattro. First up, if your Audi has a longitudinal engine, that means the engine is mounted front to back, it will use one of two Quattro systems, either the Torsen-based Quattro or the newer Quattro Ultra. On the other hand, if your Audi has a transverse engine, mounted sideways, then it's using a Haldex-based Quattro system. And finally, if your Audi is one of the few with a rear or mid-mounted engine, like the legendary R8, then it uses a special version called Performance Quattro. Starting with the most iconic, Torsen Quattro. Torsen Quattro is the most traditional and mechanical all-wheel drive system in Audi's lineup. In a longitudinal layout, the engine sits in line with the drivetrain. Behind it is the transmission, and then comes the heart of the system, a mechanical center differential, specifically a Torsen differential. Torsen stands for torque sensing, which is integrated inside the transmission housing. From the gearbox, there is a hollow input shaft. It's locked to the outer housing of the differential. When the hollow input shaft spins, the whole differential housing spins with it. Inside that spinning housing, there are two sun gears. One is connected to the front output shaft, which is aligned with and connected alongside the gearbox, feeding torque directly to the front differential, and then to the front axles. The other goes to the rear output shaft, which drives the propeller shaft to the rear end of the vehicle, eventually powering the rear differential and rear wheels. The internal layout of the Torsen also consists of a set of worm gears and planet gears around the sun gears. When the vehicle is moving in a straight line on a uniform surface, the input shaft brings torque from the transmission and gives to the housing. The worm gears connected to the housing receive and drive the sun gears, which are connected to the drive shafts. Transmit torque evenly, usually in a 50 to 50 or 40 to 60 split ratio, depending on the design. Now imagine the rear wheels hit a slippery surface and lose traction. The rear output shaft starts to spin faster than the front. Its sun gear spins faster. This makes the worm gears start turning. Worm gears resist being driven backward. That resistance creates a load that pushes torque across the gear set to the other sun gear. More torque goes to the axle with grip. In this case, to the front drive shaft, which still has grip. It can get up to 70 percent of the torque. Once traction is regained, both shafts return to equal speed. If the front wheels hit a slippery surface and lose traction, this resistance naturally redirects up to 80 percent of the torque to the rear drive shaft, which still has grip. No electronics, no delay, no clutches to wear out. It reacts purely based on mechanical torque flow and responds instantly to slipping conditions, which makes it one of the most refined AWD systems on the road. No wonder it's the heart of Audi's legendary quattro performance. Why did Audi change it? Well, Audi eventually moved away from Torsen and many of its newer models. Not because it wasn't effective, but because the automotive world changed. Fuel efficiency, weight savings, and modern electronics became top priorities. That's why Audi developed an entirely new version of quattro called Quattro Ultra. Let's see how it works. Quattro Ultra removes the traditional center differential completely. Instead, it uses two electronically controlled clutches. One multi-plate clutch behind the transmission and another clutch inside the rear differential. Under normal, dry, steady driving, the rear axle is completely disconnected. The car runs in pure front wheel drive mode. This reduces parasitic losses and saves fuel. As soon as the car detects a sharp throttle input or will slip starting at the front, the system pre-activates the clutches even before any actual wheel spin occurs. In just under 250 milliseconds, both rear axle clutches close and send up to 70% torque to the rear wheels. Now the car behaves like all-wheel drive. Now you may ask, how is it to pre-activate the clutch? That's the real genius behind this system. The car is constantly monitoring steering angle, throttle position, urate, possible understeer or oversteer, lateral g-forces, and even your drive mode like dynamic or off-road. The system checks all this data hundreds of times per second. So the system is now predicting wheel slip. In pre-activation, the multi-plate clutch starts building pressure. If grip loss looks more likely, the wheel speed sensors instantly send a signal to the control unit. Within milliseconds, the dog clutch in the rear differential engages. By the time the front tires would have slipped, all-wheel drive is already connected and transmitting torque to the rear. This makes the system feel nearly as responsive as full-time all-wheel drive, but with better fuel economy. But what if we move away from the classic longitudinal setup to the transverse engine layout, where the engine is mounted sideways? They went for something more compact and clever, the Haldex system. Here a drive shaft runs from the front gearbox to the rear axle, and just before the rear differential sits a compact Haldex coupling, the heart of this AWD system. It's a compact module that contains a wet multi-plate clutch pack, an electric actuator, a hydraulic pressure system. In normal driving, the front wheels are doing all the work. The drive shaft spins, but the Haldex clutch stays open. No torque is sent to the rear, but when traction is lost at the front, that's when Haldex steps in. Sensors pick up the difference in wheel speed. The control unit activates the electric motor, which pressurizes fluid and begins to close the multi-plate clutch pack. Now torque flows through the spinning drive shaft, into the clutch, through the rear differential, and finally to the rear wheels, restoring grip. Haldex can send up to 50% of the available torque to the rear axle. It's simple, compact, fast, and efficient, but it's not full-time all-wheel drive. But now let's take a sharp turn. What if the engine isn't in the front at all? What if it's mounted in the rear mid, just behind the seats? This is where Audi's Performance Quattro comes in, a system purpose-built for supercars like the R8. Let's begin with the components that make it work. A longitudinal V10 engine sits just ahead of the rear axle. Behind that is a 7-speed dual-clutch S-Tronic transmission, which drives the rear wheels, always. Now here's where it gets interesting. A geared output shaft runs forward from the transmission, spinning a propeller shaft that connects to the front axle. At the end of that shaft sits the real control unit, an electronically controlled multi-plate clutch inside the front differential housing, deciding how much power goes to the front wheels. In normal driving, it runs purely on rear-wheel drive. The front shaft just spins freely. But when the system senses slip, the front clutch instantly engages, sending up to 30% of torque to the front wheels. All of this happens in milliseconds, ensuring the R8 stays glued to the tarmac. But Audi isn't the only one playing with traction. Over in Munich, BMW has its own philosophy, and they call it xDrive. Unlike Audi's many quattro flavors, BMW keeps things simpler. One name, but two distinct systems depending on engine layout. BMW doesn't use rear engines at all. Every xDrive system starts with the engine mounted at the front. Let's start with a longitudinal xDrive system. Here, the engine is mounted front to back, sending power into an 8-speed ZF automatic transmission, followed by a compact transfer case. Inside this transfer case, the main input shaft continues straight through to the rear drive shaft, which means the car naturally behaves like a rear-wheel drive vehicle. But branching off that shaft is a secondary output shaft connected to the front axle through a chain drive. Between these two shafts sits an electronically controlled multi-plate clutch pack. Under normal conditions, it's rear-biased, and the clutch is slightly open 60% rear and 40% front. But when the rear wheels slip, or the system predicts slip, the clutch adjusts instantly. It can go up to 50 to 50 for maximum traction. In extreme performance modes or cornering, the clutch can fully release, sending nearly 100% torque to the rear, preserving BMW's signature balance. At the rear, most BMWs use an open differential, while M performance models get an electronically controlled limited-slip differential for torque vectoring between the left and right wheels. But not all BMWs are built this way. In compact cars, the engine is mounted transversely, and the xDrive system works differently. Here, the front transaxle drives the front wheels directly, and a drive shaft sends torque to the rear axle. At the rear, just before the differential, sits a hydraulically actuated clutch pack, similar to a Haldex system. In normal conditions, it's pure front-wheel drive to save fuel, but when slip is detected, the clutch engages to send up to 50% torque to the rear. This transverse xDrive setup focuses more on stability and safety rather than performance, offering secure handling and confident traction in all weather. Now it's time to switch to a different AWD philosophy. Same German precision, but a very different character. Meet Formatic, Mercedes-Benz take on all-wheel drive. Mercedes builds cars in only two engine layouts, longitudinal, transverse, no rear-engine Mercedes exists today. In transverse cars, the engine sits sideways. It's connected to a front transaxle that powers the front wheels. The PTU sits directly on the side of the transaxle. Its job is simple. Take a portion of the engine's torque and redirect it 90 degrees toward the rear of the car. At the very end of that shaft sits an electronically controlled multi-plate clutch pack mounted right in front of the rear differential. In normal driving, this clutch stays open. The rear wheels receive no torque and the car behaves like a pure front wheel drive vehicle. But the moment the front wheels start losing grip, the clutch pack pressurizes and begins feeding torque to the rear wheels. Depending on conditions, up to about half of the engine's torque can be sent rearward. In the more extreme AMG 45 versions, the rear axle is even more advanced. Instead of a single clutch, there are two individual clutch packs, one for each rear wheel. That means real torque vectoring. The system can overdrive the outside rear wheel during a corner. This is called the 4MATIC plus version of the transverse engine setup. Now, let's move into the longitudinal setup. Older longitudinal models use a classic mechanical transfer case mounted at the back of the transmission. Inside this transfer case, there is a planetary gear set used as a fixed center differential. It simply splits torque by design using its gear geometry. But since this split was fixed, Mercedes needed a way to control wheel slip. So they used a braking system. If a front wheel slipped, it braked that wheel, forcing torque to the other axle through the planetary gears. This was called 4ETS, electronic traction system. Then Mercedes changed everything. The planetary center differential was removed entirely. In its place, Mercedes added a wet multi-plate clutch pack controlled by an electric actuator. Here, the rear wheels are the default drive. A clutch pulls in the front wheels whenever needed. Torque split becomes fully variable. But it's not as aggressive as a 4MATIC plus, as 4MATIC plus uses a multi-plate clutch inside the differential unit in the rear for torque vectoring. If the right wheel slips, the clutch tightens and sends more torque to the left wheel. If left slips, the clutch tightens and sends more torque to the right wheel. That's how left-right torque vectoring happens. When the rear differentials multi-plate clutch locks, both rear wheels turn at the same speed. And that solid connection is exactly what the system uses to activate drift mode. And now we arrive at the legend, the G-Class. Even though it shares the same 4MATIC badge, the G-Wagon drivetrain is a completely different animal. The older G-Wagon used a separate transfer case, not mounted into the transmission. Instead, a short drive shaft connected the transmission output to the transfer case input, and two drive shafts connected to front differential and rear differential. A mechanical center differential, permanent 50 to 50 torque split, and mechanical locking for center, front, and rear differential. Yes, the driver actually gets control over three locking differentials. You have three buttons on the dashboard. First, you can lock the center differential. This forces the front and rear axles to turn together. So even if the front axle is slipping, the rear will still push you forward. Next, you can lock the rear differential. This makes both rear wheels rotate at the same speed, giving maximum traction on climbs or when one wheel lifts. Finally, you can lock the front differential. This ties both front wheels together for the toughest situations, deep mud, rocks, or when the vehicle is crossed up. And if the terrain gets really tough, you can switch the G-Wagon into low range. With one button, the transfer case drops into a lower gear ratio, slowing the wheels. When the input shaft rotates three times, the output shaft rotates only once. This multiplies torque and giving you smooth control power for crawling over rocks, steep climbs, or deep obstacles. It's basically the G-Wagon's slow but unstoppable mode. But the newer G-Wagon moved to a more compact, stronger magnesium case transfer case that sits closer to the transmission. But the internals remain old school. So that's the world of modern all-wheel drive. Different systems, different philosophies, but all built for one purpose. To keep you moving, no matter the road beneath you. Thanks for watching.