Front Wheel Drive vs Rear Wheel Drive
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[edit] Overview
Front Wheel Drive cars have an engine in front of the cabin and have the power of that engine delivered to the front wheels. Front wheel drive cars also use front wheels to steer.
Rear Wheel Drive cars may have the engine either in front ( more common ) of the cabin or behind the cabin ( less common ) and have the power delivered to the rear wheels. Rear wheel drive cars use front wheels to steer but sometimes can also use rear wheels for additional steering.
[edit] Drive Shaft
In most rear wheel drive cars the power must be transferred from the engine in the front to the differential in the rear. This power is transferred via the drive shaft.
http://en.wikipedia.org/wiki/Drive_shaft
Because drive shaft has significant weight and front wheel drive cars don't have one this theoretically makes front wheel drive cars generally lighter. However in practice the more important reason front wheel drive cars are generally lighter is because they are generally less powerful.
Transferring power to the drive shaft and then to the rear axle from the drive shaft results in some energy being lost, which means that automakers may choose front wheel drive if they want to maximize fuel efficiency.
[edit] Weight Distribution
Front Wheel Drive cars must compromise between front-rear balance and the drive wheels' traction - a typical front wheel drive car will have a 60% front 40% rear weight distribution. Since the vehicle's weight is not equally distributed to the wheels while turning or braking, which means the vehicle will not handle as well when turning or braking.
A rear wheel drive car will typically have the engine between the front wheels ( as opposed to in front of them ) and the transmission will usually be partially under the cabin. The differential and the axles will be all the way in the back. This makes a rear wheel drive inherently less nose heavy than a front wheel drive, however it will still tend to be nose heavy.
Ideal weight distribution is between approximately 53% front / 47% rear ( Lexus LFA, Nissan GTR ) and 38% front / 62% rear ( Porsche GT2 ). No front wheel drive cars have ever made it inside this range. From the rear wheel drive cars the ones that are true sports cars often do make it - examples are BMW and Corvette.
[edit] Torque Steer
Torque steer is a phenomenon where engine power feeds back through the drive wheels into the steering wheel. Torque steer manifests itself as a steering wheel that twists around erratically in the driver's hands whenever the front drive wheels don't have enough traction in a well designed car or pretty much during any hard acceleration in a poorly made car.
http://en.wikipedia.org/wiki/Torque_steer
Because rear wheel drive cars don't use front wheels as drive wheels they never have torque steer problems. Even if the rear wheel drive car also uses rear wheels for steering the rear wheels are steered by the computer and only the front wheels are mechanically linked to the steering wheel.
Torque steer is generally considered a sign of poor engineering and cheap design. No car that has excessive torque steer can not be considered a luxury car. This is one of the main reasons why luxury cars are usually rear wheel drive.
[edit] Handling
Handing is the most important characteristic of a sports car. A car that accelerates well is not a true sports car unless it also handles well. Handling refers to the ability of the car to follow driver's input during cornering.
http://en.wikipedia.org/wiki/Car_handling
Both front and rear wheel drive cars tend to understeer when the accelerator pedal is not being used. This is both a result of nose heavy weight distribution as well as a design safety feature. In a rear wheel drive car however accelerator application can either remove understeer or create oversteer ( depending on speed and pedal position ) giving the driver control of the car. In a front wheel drive car the understeer is always present and accelerator application only makes it more severe. Front wheel drive cars therefore can never have adequate handling for a true sports car and this is why no true sports car company ( porsche, ferrari, lamborgini, bugatti etc. ) ever makes front wheel drive cars.
[edit] Applications
Because front wheel drive cars are both poorly suited for luxury cars and completely unsuitable for sports cars the net effect is that no car over $100,000 uses front wheel drive. Front wheel drive cars are typically used where the extra weight and cost of the shaft drive is deemed prohibitive or where the driver is not expected to possess the skill required to control rear wheel drive cars.
People who buy front wheel drive cars usually cite the ability to tackle rain and snow as the reason for not getting rear wheel drive. While it is true that front wheel is better than rear wheel drive in the snow it is usually not the real reason. People who want the very best snow and mud performance typically get all wheel drive. Front wheel drive's primary advantages over rear- or all-wheel-drive are initial cost and fuel-efficiency.
[edit] All Wheel Drive
When properly engineered ( as in the Nissan GTR ) all wheel drive provides better traction and handling than either front- or rear-wheel-drive. In practice most car makers possess neither the know how to pull it off nor are willing to spend the kind of money that it would take. A typical all wheel drive car tends to be more like the average of the two than the best of both. All wheel drive cars do have the best snow and mud performance but the price for that is greater cost, weight and lower fuel efficiency.
