RWD vs FWD

[pitbullz]

pardon me for my ignorance but whats the difference in terms of handling etc between a front and rear wheel driven vehicle?

[Bogeyman]

From wikipedia.org:

Rear wheel drive
Advantages:

Better handling in dry conditions - less force is applied to the front wheels, allowing more of their friction to be used to steer the vehicle and allowing more power to be applied through the rear wheels, which are unburdened by steering.

Less costly and easier maintenance - Rear wheel drive is mechanically simpler and typically does not involve packing as many parts into as small a space as does front wheel drive, thus requiring less disassembly or specialized tools in order to replace parts.

No torque steer.

Even weight distribution - The division of weight between the front and rear wheels has a significant impact on a car's handling, and it is much easier to get a 50/50 weight distribution in a rear wheel drive car than in a front wheel drive car, as more of the engine can lie between the front and rear wheels (in the case of a mid engine layout, the entire engine), and the transmission is moved much farther back.

Towing - Rear wheel drive puts the wheels which are pulling the load closer to the point where a trailer articulates, helping steering, especially for large loads.

Weight transfer during acceleration. (During heavy acceleration, the front end rises, and more weight is placed on the rear, or drving wheels).

Drifting - Drifting is a controlled skid, where the rear wheels break free from the pavement as they spin, allowing the rear end of the car to move freely left and right. This is of course easier to do on slippery surfaces. Severe damage and wear to tires and mechanical components can result from drifting on dry asphalt. Drifting can be used to help in cornering quickly, or in turning the car around in a very small space. Many enthusiasts make a sport of drifting, and will drift just for the sake of drifting. Drifting requires a great deal of skill, and is not recommended for most drivers. It should be mentioned that front wheel drive and four wheel drive cars may also drift, but only with much more difficulty. When front wheel drive cars drift, the driver usually pulls on the emergency brake in order for the back wheels to stop and thus skid. This technique is also used for 'long' drifts, where the turn is accomplished by pulling the e-brake while turning the steering wheel to the direction the driver desires. With drifting, there is also the importance of 'counter-steering' - where while temporarily out of control, the driver regains it by turning the wheel in the opposite direction and thus preparing for the next turn or straight-away.

Disadvantages:

More difficult to master - While the handling characteristics of rear-wheel drive may be useful or fun in the hands of someone who knows how to use them, in the hands of most drivers, having the rear wheels move about is unintuitive and dangerous. Rear wheel drive rewards skill, and punishes the lack of it. Other layouts are much more forgiving, but don't offer the same rewards in handling.

Decreased interior space - This isn't an issue in a vehicle with a ladder frame like a pickup truck, where the space used by the drive line is unusable for passengers or cargo. But in a passenger car, rear wheel drive means: Less front leg room (the transmission tunnel takes up a lot of space between the driver and front passenger), less leg room for center passengers (there is also a smaller tunnel for the drive shaft), and sometimes less trunk space (since there is also more hardware that must be placed underneath the trunk).

Increased weight - The components of your typical rear wheel drive vehicle's power train may be less complex, but there are more of them. The driveshaft adds weight. The transmission is probably heavier. There is extra sheet metal to form the transmission tunnel. There is a rear axle or rear half-shafts. A rear wheel drive car will weigh slightly more than a comparable front wheel drive car (but less than four wheel drive).

Higher purchase price - Probably due to more complicated assembly (the powertrain is not one compact unit) and added cost of materials, rear wheel drive is typically slightly more expensive to purchase than a comparable front wheel drive vehicle. This might also be explained by production volumes, however.

More difficult handling on low grip surfaces (wet road, ice, snow, gravel...) as the car is pushed rather than pulled.

Oversteer and the related problem of fishtailing.


Front wheel drive
Advantages:

Packaging efficiency - the powertrain is a single unit contained in the engine compartment of the vehicle, obviating the need to devote interior space for a driveshaft tunnel or rear differential and increasing the volume available for passengers and cargo.

Cost - Fewer components overall.

Improved drivetrain efficiency - the direct connection between engine and transaxle reduce the mass and mechanical inertia of the drivetrain compared to a rear-wheel drive vehicle with a similar engine and transmission, allowing greater fuel economy.

Assembly efficiency - the powertrain can be often be assembled and installed as a unit, which allows more efficient production.

Slippery-surface traction - placing the mass of the drivetrain over the driven wheels improves traction on wet, snowy, or icy surfaces.

Predictable handling characteristics - front-wheel drive cars, with a front weight bias, tend to understeer at the limit, which is commonly believed to be easier for average drivers to correct than terminal oversteer, and less prone to result in fishtailing or a spin.

Disadvantages:

The center of gravity of the vehicle is typically further forward than a comparable rear-wheel drive layout. In front wheel drive cars, the front axle typically supports around 2/3rd of the weight of the car (quite far off the "ideal" 50/50 weight distribution). This is a contributing factor towards the tendency of front wheel drive cars to understeer.

Torque steer can be a problem on front wheel drive cars with higher torque motors(> 210 Nm ). This is the name given to the tendency for some front wheel drive cars to pull to the left or right under hard acceleration. It is a result of the offset between the point about which the wheel steers (which falls at a point which is aligned with the points at which the wheel is connected to the steering mechanisms) and the centroid of its contact patch. The tractive force acts through the centroid of the contact patch, and the offset of the steering point means that a turning moment about the axis of steering is generated. In an ideal situation, the left and right wheels would generate equal and opposite moments, cancelling each other out, however in reality this is less likely to happen. Torque Steer is often incorrectly attributed to differing rates of twist along the lengths of unequal front drive shafts.

Lack of weight shifting will limit the acceleration of a front wheel drive vehicle. In a rear wheel drive car the weight shifts back during acceleration giving more traction to the driving wheels. The fact that this does not happen in a front wheel car is the main reason why nearly all racing cars are rear wheel drive. However, since front wheel cars have the weight of the engine over the driving wheels the problem only applies in extreme conditions.

In some towing situations front wheel drive cars can be at a traction disadvantage since there will be less weight on the driving wheels. Because of this, the weight that the vehicle is rated to safely tow is likely to be less than that of a rear wheel drive or four wheel drive vehicle of the same size and power.

Due to geometry and packaging constraints, the CV joints (constant-velocity joints) attached to the wheel hub have a tendency to wear out much earlier than their rear wheel drive counterparts. The significantly shorter drive axles on a front wheel drive car causes the joint to flex through a much wider degree of motion, compounded by additional stress and angles of steering, while the CV joints of a rear wheel drive car regularly see angles and wear of less than half that of front wheel drive vehicles.

The driveshafts may limit the amount by which the front wheels can turn, thus it may increase the turning circle of a front wheel drive car compared to a rear wheel drive one with the same wheelbase.

Snap oversteer. The virtue of weight over the drive wheels also makes the rear end of the car exceptionally light. In a hard cornering situation, slight weight transfer to the front of the car can easily result in a unrecoverable spin.

[the_wildthing]

http://tsikot.yehey.com/forums/showthread.php?t=10305

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