Why, usually the engine of a two-wheeler pulls rear wheel and that of a four wheeler pulls front wheels?

Question

I mean, why is it that generally the engine of two wheeler pulls rear wheel rather than the front one and in case of four wheeler's engine, it is placed to pull front wheels rather than rear wheels. Please answer with proper explanation.

Answer 1

That's a bit of a generalisation, not all vehicles are front-wheel drive - there are rear-wheels drives too, depending on manufacturers' inclination, ...and now we have 4-wheel drives.

Advantages of front-wheel drive
Interior space: Since the powertrain is a single unit contained in the engine compartment of the vehicle, there is no need to devote interior space for a driveshaft tunnel or rear differential, increasing the volume available for passengers and cargo.
Cost: Fewer components overall
Weight: Fewer components mean lower weight
Improved fuel efficiency due to less weight
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 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 stand-still traction on wet, snowy, or icy surfaces, although heavy cargo can be beneficial for traction on rear-wheel drive pickup trucks.
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.
Better crosswind stability.
Tactile feedback via the steering wheel informing driver if a wheel is slipping.
Front-wheel drive allows the use of left-foot braking as a driving technique. However this mostly applies to rally cars.
While driving on snow or ice, the skilled driver can control the movement of the car even while skidding by steering, throttling and pulling the hand brake (given that the hand brake operates the rear wheels as in most cases, with early Saabs being an exception). It takes practice to master but it vastly increases safety while driving in cold environments, given that the driver understands the risks involved in intentional skidding.

Disadvantages of front-wheel drive
The centre of gravity of the vehicle is typically farther 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 in the tendency of front wheel drive cars to understeer.
Torque steer can be a problem on front-wheel drive cars with higher torque engines (more than 210 N·m ) and transverse layout. 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. However, Centre-point steering geometry can be incorporated in the design to avoid torque steer. This is how the powerful Citroën SM avoided the problem.
Lack of weight shifting will limit the acceleration of a front-wheel drive vehicle. In a vehicle, the weight shifts back during acceleration, giving more traction to the rear wheels. This is the main reason why nearly all racing cars are rear-wheel drive. However, since front-wheel drive 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 the universal joints typically used in 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.

Advantages of Rear-wheel drive
Better handling in dry conditions - accelerating force is applied to the rear wheels, on which the down force increases, due to load transfer in acceleration, making the rear tires better able to take simultaneous acceleration and curving than the front tires.[1]
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, which is an effect in front wheel drive cars caused by large amounts of torque affecting steering in such a way as to make the front wheels oscillate from side to side under heavy acceleration.[citation needed]
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.
Steering radius - As no complicated drive shaft joints are required at the front wheels, it is possible to turn them further than would be possible using front wheel drive, resulting in a smaller steering radius for a given wheelbase.
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 driving wheels.

Disadvantages of Rear-wheel drive
On snow and ice, rear-wheel drive loses its traction advantage to front or all-wheel drive vehicles which have greater weight on the driven wheels.
Decreased interior space - In a passenger car, rear wheel drive means: Less front leg room as the transmission tunnel takes up a lot of space between the driver and front passenger, less leg room for center rear passengers (due to the tunnel needed for the drive shaft), and sometimes less trunk space (since there is also more hardware that must be placed underneath the trunk). There are some exceptions to this as rear engine designs do not take away interior space. (See Porsche 911, and Volkswagen Beetle)
Increased weight - The components of a rear wheel drive vehicle's power train are less complex, but they are larger. 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. Or it could be explained by the fact that the majority of rear-wheel cars are in the sports/performance/luxury categories. Few "family" sedans have rear-wheel drive. So a cost comparision is not necessarily possible.[citation needed]
Oversteer (also deliberately used in drifting) and the related problem of fishtailing.
A slight loss in the mechanical efficiency of the drivetrain (approximately 17% coastdown losses between engine flywheel and roadwheels compared to 15% for front wheel drive). The reason is the need for the drive to "turn the corner" at the rear differential by means of a pinion and crownwheel. Mid- and rear-engined cars using a transverse layout will not have this problem.

Answer 2

There was a time when most cars were rear-wheel drive. That most cars are now front-wheel drive is a fairly recent phenomenon (about 20 years or so). Anabelezenith gave an excellent explanation about both designs, though I should add that sometimes the engine is in the rear on some rear-wheel drive vehicles (mostly sports cars and race cars, but fork-lifts too). On a two wheeler the front wheel is always used for steering because that's more stable (there are a few odd bicycles that break this rule and there may be some strange experimental vehicles that tried something differrent), so the drive wheel is in the back. It would be possible to drive the front steering wheel on a motorcycle, but the mechanics would be exceedingly complex.

Answer 3

Today's generation of AWD vehicles incorporates Subaru's old technology of having a primarily front-wheel drive and use the back wheels upon demand. Overall, it makes for the best system since a FWD vehicle is very hard to get stuck....it has better traction than a RWD. It also eliminates a lot of bulk by incorporating the transfer into the tailshaft of the transmission using a clutch system rather than an entirely different gear box. Hope this explains it. Have a great day.

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Answer 5

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Answer 6

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