The drivetrain in a car is comprised mostly of the engine and transmission. The rest of it - the parts that take power from the transmission and send it to the wheels - these are the parts that really define how the car acts on the road. Different arrangements work for different environments and they all provide different experiences for the driver. Manufacturers and brand-loyal enthusiasts like to spout numbers and specs, but what do the different drivetrain arrangements really offer?
Front-wheel drive vehicles are known for being lighter, on average, than either of their counterparts. The layout of the drivetrain also leaves lots of space under the car where a driveshaft, center differential, etc. would normally go. This means that manufacturers can keep the drivetrain in a neat little package on one end of the car while giving the passengers more legroom and trunk space.
How Does It Work?
Without going into too much detail, all of the normal drivetrain components are present in a front-wheel drive car with the only difference being their orientation and location. You will find the engine, transmission, and differential all connected to a transversely-mounted engine.
Longitudinally-mounted engines sending power to the front wheels do exist, but they are very uncommon and have a layout similar to all-wheel drive cars anyway, meaning the power usually goes back to the transmission under the car between the driver and passenger before going to a differential in the same housing, sending it out to the front wheels. This is like Subaru’s Symmetrical All-Wheel Drive without the driveshaft sending power to the rear axle.
In a car with a transversely-mounted engine, the cylinders are in line left-to-right rather than front-to-back.
While this arrangement may seem counterintuitive, it actually allows for a lot of important components to occupy a small area while performing like a much more complex drivetrain most of the time. A transversely-mounted engine can have the transmission sitting basically next to it (still between the front wheels), sending power down to the front differential and subsequently to the the axles. The assembly of the transmission, differential, and axles in one housing is called a transaxle.
This kind of setup can be found on rear or mid-engine cars as well, the only difference being the location (on the rear axle).
This light and simple arrangement allows manufacturers to put smaller, more efficient engines under the hood.
Front-Wheel Drive Advantages
Front-wheel drive cars are generally lighter and have the most weight over the front wheels. This provides a good balance for reliable traction. This also helps with braking.
Fuel efficiency is a big selling point for cars with this type of drivetrain. While superior traction makes them use fuel more effectively regardless of the engine size, the smaller engines use less gas and the light weight means the engine has less to lug around.
Traction in the rear wheels is significantly better when they are not putting power to the ground. Lots of lateral stress is put on the vehicle when going around corners, making the rear wheels fight to keep traction. When the rear wheels do not succeed in keeping traction, oversteer happens.
Oversteer is when the rear end comes loose because the rear wheels lose traction and this can make the vehicle lose control.
No drivetrain components that take up lots of space are under the vehicle, letting the body sit lower and allowing the passengers to have more space.
The handling characteristics are predictable and less aggressive than other drivetrain layouts. New drivers or cautious drivers benefit from this.
Front-Wheel Drive Disadvantages
With front-wheel drive, the front wheels are taking on a lot of work. They are responsible for steering, most of the braking, and all of the power that goes to the ground. This can cause traction problems and understeer.
Understeer is when the front wheels lose traction while turning, making the car drift towards the outside of the turn.
The front wheels can only tolerate so much horsepower before they are no longer useful for cornering quickly. While everyone loves a car with some kick, too much power makes the front wheels lose traction dramatically. This can make a dry, paved road feel like a sheet of ice.
Is Front-Wheel Drive Right for Your Needs?
Cities and urban environments are ideal for front-wheel drive. The roads are usually well-maintained and there are not many open stretches where high-speed driving and cornering could occur.
Commuters and other consistent longer-distance drivers will enjoy the straightforward maintenance and fuel economy front-wheel drive cars offer.
New drivers should start with a front-wheel drive car. This can let them learn to drive in an easy-to-control car and will not let them do too much dangerous nonsense like donuts and powerslides
Front-wheel drive cars have better traction in slippery road conditions compared to rear-wheel drive cars. Anyone living in an area with light snow or lots of rain will benefit from a front-wheel drive car.
A favorite among automotive purists, rear-wheel drive still has a lot to offer today’s driver. Mostly found in sports and luxury cars nowadays, this arrangement was used in nearly every vehicle made in the first half of the Twentieth century. The main draw is the intuitive layout and precise handling characteristics that rear-wheel drive offers. The rear-wheel drive layout is often seen as the standard layout for a car.
How Does It Work?
The most straightforward drivetrain arrangement, rear-wheel drive puts the engine at the front of the car and sends it back through the transmission to the rear differential. The differential then sends power to the rear wheels. Simple models and books aimed at young people and children almost always portray this as “how a car works,” and for good reason. On top of the fact that the flow of power from front to back is visually easy to understand, having one axle handle power while the other steers makes a lot of sense.
The standard layout has the engine longitudinally-mounted at the front with the transmission sitting under the car between the driver and passenger. The driveshaft goes through a tunnel built into the body. A handful of sports cars like the Mercedes SLS AMG have the transmission at the back in the form of a rear transaxle, but this arrangement is technically complex and only found on high-end sports cars race cars. Rear-engine rear-wheel drive cars also use a rear transaxle, keeping all of the weight over the drive wheels for superior traction.
Handling is the biggest factor to those who love rear-wheel drive. The handling characteristics are predictable but very lively. Rear-wheel drive cars can usually be made to oversteer corners with relative ease. Some view this as a problem, others enjoy it so much that whole motorsports are built around the principle. Drifting is the only motorsport where drivers are judged on style over speed. Specifically, they are judged on how well they can control their car’s oversteer around corners and how close they can get to walls and other obstacles without fully hitting them.
Oversteer is like espresso. Some people can’t live without it, while it makes others feel totally out of control. Also, too much will give you a stomach ache and the crash that follows when you overdo it can really make you reevaluate your priorities.
Large, luxurious sports cars like the BMW M5 or the Cadillac CTS-V use rear-wheel drive to give the larger vehicles more agile handling. While all-wheel drive works for performance applications as well, it also promotes understeer more than rear-wheel drive. This is a big problem for heavier cars who need the sharpest handling possible to move quickly through corners without tricky maneuvering.
Rear-Wheel Drive Advantages
Precise handling, as the front wheels are not putting any power to the ground and losing traction.
Less weight in the front combined with no power at the front wheels means very little chance of understeer.
Intuitive layout that makes troubleshooting easier. The location of a noise or vibration is easy to pinpoint with the whole drivetrain going front-to-back in a line.
Rear-Wheel Drive Disadvantages
Poor traction in slippery conditions due to having very little weight over the drive wheels. Some drivers put bags of sand over their rear wheels in the winter, reducing gas mileage to provide better traction.
Some people argue that rear-wheel drive is outdated, citing advancements with all-wheel and front-wheel drive that make them perform similarly. In some cases, rear-wheel drive cars are made that way to capture nostalgia. This is the case with the Ford Mustang and the Dodge Challenger.
If a rear-wheel drive car has a live axle at the back, i.e. an axle without independent suspension, then the handling can be clunky and uncomfortable.
Does Rear-Wheel Drive Work for Your Needs?
Drivers living in a warm area that doesn’t get particularly excessive rainfall will not experiences most of the drawbacks with rear-wheel drive.
Those wanting a sporty feel can achieve that in even a non-sporty vehicle that has rear-wheel drive.
Powering just the rear wheels rather than all of the wheels makes for better fuel economy than all-wheel drive and allows for better acceleration at speed.
All-wheel drive has been gaining in popularity for the last two decades. Originally, manufacturers thought that all-wheel drive would mainly draw in those looking to travel off-road. They found instead, that many people loved the way all-wheel drive cars handled on the pavement and dirt roads at higher speeds. Rally racing, taking place off-road most of the time, adopted all-wheel drive very quickly. Because rally racing was founded in order to race cars that normal people could go and buy off the lot, manufacturers had to make sporty all-wheel drive cars available from the factory to meet homologation regulations. This means that in order to race a car in rally races, the manufacturer would have to make a certain number per year for consumers. Sedans like the Mitsubishi Lancer and Subaru Impreza were made in large numbers while faster Group B cars like the Ford RS200 were made in quite small numbers.
This really pushed car manufacturers to start integrating all-wheel drive into their sportier cars. This also meant that more advanced and lightweight all-wheel drive systems were developed to stay competitive. Nowadays, all-wheel drive is a standard feature in everything from station wagons to supercars. Even Ferrari has used all-wheel drive in two recent vehicles.
How Does It Work?
All-Wheel drive is usually found in vehicles with the engine at the front. While Audi and Porsche both make models with all-wheel drive that don’t have the engine in the front, the pool of vehicles that description applies too is still tiny. With front-engine cars, there are two common ways that the all-wheel drive works:
The system that distributes power the most evenly involves sending power through the transmission and into a center differential. This is similar to a rear-wheel drive layout, only with a driveshaft running from the center differential to a differential on the front axle. In the case of the Nissan Skyline GT-R, a rare car in the US, the base model was actually a rear-wheel drive car. Audi’s Quattro system uses this layout as well. The power split between the two axles is usually 50/50 or favoring the rear wheels up to a 30/70 split.
The second type of all-wheel drive layout looks more like that of a front-wheel drive car. The engine connects to the transmission that is in the same housing as the front differential and axles. Coming from this assembly is another driveshaft running to a rear differential. Honda, MINI, Volkswagen, and many others use systems like these with great results. This type of system usually favors the front wheels, with a 60/40 split being the average in higher-performance cars. Some systems send as little as 10% of power to the rear when the front wheels aren’t slipping. Fuel economy improves with this system, and it weighs less than the alternative.
All-Wheel Drive Advantages
Traction is greatly improved with power going to all of the wheels. This greatly improves performance off-road and on rough roads. This also improves acceleration in performance applications.
Easily the most versatile drivetrain arrangement. A big reason all-wheel drive cars are popular with tuners and weekend warriors is the array of things they can do on and off-road.
Weather is hardly a worry when your car can send power to whatever wheels have the most traction. Snow and rain are easier to drive in.
All-Wheel Drive Disadvantages
Better traction in slippery road conditions can make a driver over-confident in their ability to stop or turn, often resulting in an accident.
Worse fuel economy than the alternatives.
Heavy. More parts means more weight no matter how you cut it.
More parts mean more things that can go wrong. Worse yet, there is no real standard all-wheel drive system so the parts are not as swappable as they are with rear-wheel drive vehicles.
Unusual handling characteristics; every manufacturer has their own quirks in this department. That said, some all-wheel drive systems are ridiculously easy to handle while others are terrifyingly unpredictable (particularly when modified).
Is All-Wheel Drive Right for Your Needs?
Anyone living in a very snowy area should seriously consider owning an all-wheel drive vehicle. Getting stuck in the snow can be particularly bad in rural areas.
Those living in warm, dry places won’t need all-wheel drive for extra traction but still my enjoy the performance aspect. Worse fuel economy though.
Usually all-wheel drive is overkill in the city. Smaller all-wheel drive vehicles can be wonderful in snowy cities like Montreal or Boston though.
This article originally appeared on YourMechanic.com as Comparisons of Drivetrains - FWD, RWD, AWD and was authored by Ian Swan.