From chain drives to electronic AWD
The very first automobiles drove their rear wheels through bicycle-style chains (Benz, Daimler, early Mercedes). The propeller shaft and live rear axle that defined the next century of RWD arrived around 1898 with Louis Renault's Type A. The Cugnot steam carriage (1769) had been front-driven, but FWD didn't go mainstream until the Citroën Traction Avant (1934) and was perfected for the masses by the Mini (1959) and Volkswagen Golf (1974). Four-wheel drive existed in 1903 (the Spyker 60HP), became famous in the WWII Willys MB Jeep, and crossed over to performance with the 1980 Audi quattro that dominated Group B rally and forced every manufacturer to take AWD seriously. The Nissan GT-R's ATTESA E-TS (1989) and Porsche's PTM brought electronically controlled, computer-managed torque distribution to the street. The 2018 Rimac Concept_One and 2023 Nevera, with one independent motor at each wheel, finally realized the dream of true per-wheel torque vectoring with no mechanical differential at all.
How drivetrain components are made
Driveshafts are precision-balanced steel or carbon-composite tubes with forged yokes welded to each end and either U-joints or constant-velocity (CV) joints attached. Halfshafts are forged steel splined to the differential at one end and the hub at the other, each end with a sealed CV joint packed with high-pressure moly grease and protected by a rubber boot. The differential carrier is cast iron or aluminum machined to hold tapered roller bearings and the ring-and-pinion gear set — that gear set is the most expensive single part of the axle, hypoid-cut from heat-treated steel and lapped in matched pairs to control noise. Transfer cases (in AWD/4WD vehicles) bolt to the back of the transmission and add a planetary or chain-driven splitter plus a clutch pack or viscous coupling that decides how torque flows to the front axle. Final assembly fills each unit with the precise spec gear oil — typically a 75W-90 GL-5 with friction modifier for clutch-type LSDs.
How drivetrains are tested
A 4-poster shaker rig simulates uneven road inputs while the drivetrain runs under load. A roller dyno measures actual torque at each wheel so engineers can confirm the center diff is splitting power as commanded. Slip-simulator rigs spin one wheel on a low-friction roller while the others sit on grip — the AWD controller has milliseconds to detect the slip and redirect torque, and engineers log every decision. Climate-chamber durability cycles spin the axles at sustained 200 km/h with full torque for hundreds of hours to find seal failures and bearing wear. NVH (noise/vibration/harshness) chambers chase the whines and clunks that result from gear-tooth contact patterns or bushing compliance. Finally, validation fleets do real-world torture: Land Rover's Eastnor Castle off-road course, Audi's snow runs in Sweden, GT-R durability laps at the Nürburgring, and tow tests up Davis Dam with the trailer at GVWR maximum.
The different types of drivetrains
RWD (Mustang, BMW 3/M, Porsche 911, Lexus LC, every supercar): engine drives the rear wheels, fronts only steer — ideal balance, best traction under acceleration. FWD (Civic, Golf, Camry): engine drives the front wheels through a transaxle — cheap to package, great in snow, limited to ~300 hp before torque steer takes over. AWD (Audi quattro, Subaru Symmetrical, Mercedes 4Matic, Porsche PTM, Nissan GT-R): power to all four wheels through a center differential or clutch pack. Part-time 4WD (Wrangler, Land Cruiser, F-150 4x4): low-range transfer case with locked driveshafts — off-road only. On-demand AWD (CR-V, RAV4): FWD until slip, then a clutch engages the rear axle. Torque-vectoring AWD (Acura NSX, Audi RS3, AMG E63 S): clutch packs in the rear diff actively over-drive the outside wheel through a corner. Quad-motor (Rimac Nevera, Lotus Evija, Rivian R1T): an independent motor at each wheel — infinite torque distribution, no mechanical diff required.
Rear-wheel drive (RWD)
Power goes from the transmission through a driveshaft to a rear differential, which splits it to the rear wheels. The front wheels handle steering only. Weight transfers rearward under acceleration, planting the driven wheels for better launch — that's why almost every sports car and supercar is RWD or AWD with a rear bias. The classic balance of the Mazda Miata, BMW M3/M4, Lexus LC and Porsche 911 lives here. The downside: in snow or rain the rear can step out, and 50/50 weight distribution requires engineering effort (transaxle layout, mid-mounted engine).
Front-wheel drive (FWD)
The engine drives the front wheels through a transaxle that combines transmission and differential. Cheaper to package (no driveshaft tunnel), better interior space, safer in snow because the heavy engine sits over the driven wheels. Constant-velocity (CV) joints let the front wheels steer while still receiving torque. Limited to about 300 hp before torque steer (the car pulling left or right under throttle) makes it undriveable — the Honda Civic Type R is the high-water mark with 315 hp tamed by clever geometry and a helical LSD.
Rear- vs mid- vs front-engine
Front engine, RWD (Mustang, M3, 8 Series): traditional and predictable. Front engine, FWD (Civic, Golf): efficient and roomy. Mid-engine, RWD (Ferrari 296, McLaren 750S, Lotus Emira): mass over the rear axle plus polar moment near the center = ideal handling. Rear-engine, RWD (Porsche 911): mass behind the rear axle gives unmatched traction but loads up the rear at the limit. Front-engine, AWD (Audi S4, Subaru WRX): nose-heavy but composed all-weather grip.
All-wheel drive (AWD)
Some torque to every wheel, all the time or on demand. A center differential or transfer case splits torque front-to-rear. Audi quattro, Subaru Symmetrical AWD, Porsche's PTM, Mercedes 4Matic and the Nissan GT-R's ATTESA system have made AWD the default for high-power performance cars. A center clutch decides how much power goes front vs rear, often adjusting hundreds of times per second based on slip, throttle, steering angle and yaw rate.
Part-time 4WD vs full-time AWD
Traditional 4WD (Jeep Wrangler, Toyota Land Cruiser, Ford F-150 4x4) uses a transfer case with 2WD-High, 4WD-High and 4WD-Low ranges. It locks front and rear driveshafts together — great for off-road but illegal on dry pavement because the driveshafts wind up. Full-time AWD has a center differential that allows the driveshafts to rotate independently, so it's safe on any surface.
Torque-on-demand and disconnects
Many crossovers (Honda CR-V, Toyota RAV4, Ford Edge) are FWD most of the time and engage the rear axle via a clutch pack only when slip is detected — saves fuel at the cost of a moment of slip before AWD engages. Disconnect AWD (Jaguar F-Pace, some Land Rovers) physically decouples the rear driveshaft at cruise to eliminate parasitic loss entirely.
Torque vectoring
Modern AWD doesn't just split power front/rear — it sends different amounts to the left and right wheels. The Acura NSX, Audi RS3, BMW M5 and Mercedes-AMG E63 S use clutch packs in the rear differential to actively rotate the car through corners (the outside rear wheel gets more torque, pivoting the car). The Rimac Nevera goes further: independent motors at every wheel mean infinite torque distribution — the car can literally turn in place using only motor torque (Tank Turn, demonstrated by Rivian).
Differentials: open, LSD, locker
An open differential lets each wheel spin freely — great for smooth turns, terrible for traction (one wheel spinning means all the torque goes to that wheel and zero to the one with grip). Limited-slip differentials (LSDs) use clutches (mechanical clutch-type), gear preload (Torsen, helical) or pumps/clutches under hydraulic pressure to send torque to the wheel with grip. Lockers (selectable in off-roaders) mechanically force both wheels to spin together — maximum traction, but the diff binds in tight turns on grippy surfaces.
Electronic differentials
Many modern cars (BMW M, Mercedes-AMG, Ford Mustang Dark Horse, Corvette Z06) use electronically controlled multi-plate clutch differentials that can vary lockup from 0 to 100% in milliseconds based on ESC, traction control and yaw inputs. The result is open-diff smoothness in normal driving and full-lock traction on demand — without the binding and noise of a mechanical locker.
Driveshafts, CV joints and U-joints
A driveshaft transmits torque from transmission to differential. U-joints handle small angle changes between two shafts but introduce velocity variation; double-cardan or constant-velocity joints cancel that variation for smoothness. Axle halfshafts use CV joints at both ends so the wheels can move up and down with the suspension while still receiving torque. Worn CV joints click on tight turns and eventually fail outright.
Wheel hubs, bearings and unsprung mass
Hubs carry the wheel and route torque from the axle to the brake rotor and rim. Wheel bearings (sealed roller or angular-contact) support side and axial loads. Everything past the spring — wheels, tires, brakes, hubs, lower arms — counts as unsprung mass. Reducing it (forged wheels, carbon-ceramic rotors, aluminum suspension arms) is the single biggest handling upgrade because it lets the suspension control the wheel rather than the wheel pushing the suspension around.
