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    [Study Material] | [Mr. Kartik Suthar]


  • Prepared by: Kartik Suthar

    Q. Explain various vehicle layout and also state advantage and

    disadvantage for front engine front wheel drive and rear engine

    rear wheel drive.

    In automotive design, the automobile layout describes where on the vehicle

    the engine and drive wheels are found. Many different combinations of engine location

    and driven wheels are found in practice, and the location of each is dependent on the

    application for which the vehicle will be used. Factors influencing the design choice

    include cost, complexity, reliability, packaging (location and size of the passenger

    compartment and boot),weight distribution, and the vehicle's intendedhandling


    Front-wheel-drive layouts

    Front-wheel-drive layouts are those in which the front wheels of the vehicle are driven.

    The most popular layout used in cars today is the front-engine, front-wheel drive, with

    the engine in front of the front axle, driving the front wheels.

    As the steered wheels are also the driven wheels, FF (front-engine, front-wheel-drive

    layout) cars are generally considered superior to FR (front-engine, rear-wheel-drive

    layout) cars in conditions such as snow, mud, or wet tarmac. The weight of the engine

    over the driven wheels also improves grip in such conditions. However, powerful cars

    rarely use the FF layout because weight transference under acceleration reduces the

    weight on the front wheels and reduces their traction, limiting the torque which can be

    utilized. Electronic traction control can avoid wheel spin but largely negates the benefit of

    extra torque/power.

  • Prepared by: Kartik Suthar


    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.

    Weight: Fewer components usually means 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.

    Placing the mass of the drivetrain over the driven wheels moves the centre of

    gravity farther forward than a comparable rear-wheel-drive layout,

    improving traction and directional stability on wet, snowy, or icy surfaces.


    Front-engine front-wheel-drive layouts are "nose heavy" with more weight

    distribution forward, which makes them prone to understeer, especially in high

    horsepower applications.

    Torque steer is 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 (it is aligned with the points where the wheel is connected

    to the steering mechanisms) and the centroid of its contact patch. 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.

    Traction can be reduced while attempting to climb a slope in slippery conditions

    such as snow- or ice-covered roadways.

    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 counterpart.

    Turning circle FF layouts almost always use a Transverse engine ("east-west")

    installation, which limits the amount by which the front wheels can turn, thus

    increasing the turning circle of a front-wheel-drive car compared to a rear-wheel-

    drive one with the same wheelbase.

  • Prepared by: Kartik Suthar

    Rear-wheel-drive layouts


    Even weight distribution The layout of a rear-wheel-drive car is much closer to

    an even fore-and-aft weight distribution than 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


    Weight transfer during acceleration During heavy acceleration, weight is placed

    on the rear, or driving wheels, which improves traction.

    Better braking the more even weight distribution helps prevent lockup from the

    rear wheels becoming unloaded under heavy braking.

    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.


    On snow, ice and sand, rear-wheel drive loses its traction advantage to front- or all-

    wheel-drive vehicles, which have greater weight on the driven wheels. This issue is

    particularly noticeable on pickup trucks, as the weight of the engine and cab will

    significantly shift the weight from the rear to the front wheels.

    Some rear engine cars (e.g., Porsche 911) can suffer from reduced steering ability

    under heavy acceleration, because the engine is outside the wheelbase and at the

    opposite end of the car from the wheels doing the steering although the engine

    weight over the rear wheels provides outstanding traction and grip during


    A rear-wheel drive vehicle with four-wheel drive, compared to a front-wheel drive

    vehicle with four-wheel drive, will have a less efficient interior packaging since the

    transmission is often under the front passenger compartment between the two seats,

    whereas the latter can package all the components under the hood.

    Increased weight The components of a rear-wheel-drive vehicle's power train are

    less complex, but they are larger. The driveshaft adds weight. There is extra sheet

    metal to form the transmission tunnel. There is a rear axle or rear half-shafts, which

    are typically longer than those in a front-wheel-drive car. A rear-wheel-drive car will

    weigh slightly more than a comparable front-wheel-drive car (but less than four-

    wheel drive).

  • Prepared by: Kartik Suthar

    Four-wheel-drive layouts

    Most 4WD layouts are front-engine and are derivatives of earlier front-engine, two-

    wheel-drive designs. They fall into two major categories:

    Front-engine, rear-wheel drive derived 4WD systems, standard in most sport utility

    vehicles and in passenger cars, (usually referred to front engine, rear-wheel

    drive/four-wheel drive).

    Transverse and longitudinal engine 4WD systems derived almost exclusively

    from front-engine, front-drive layouts, fitted to luxury, sporting and heavy duty

    segments, for example the transverse-engine Mitsubishi 3000GT VR-4 and Toyota

    RAV4 and the longitudinal-engine Audi Quattro and most of the Subaru line.

    Rear-engine, rear-wheel-drive layout

    Most of the traits of the RR configuration are shared with the mid-engine, or MR.

    Placing the engine near the driven rear wheels allows for a physically smaller, lighter,

    less complex, and more efficient drivetrain, since there is no need for a driveshaft,

    and the differential can be integrated with the transmission, commonly referred to as

    a transaxle.

  • Prepared by: Kartik Suthar

    Rear-engine, front-wheel-drive layout

    A rear-engine, front-wheel-drive layout is one in which the engine is behind the rear

    wheels, but drives the front wheels via a driveshaft, like a conventional front-engine,

    rear-wheel-drive vehicle traveling in reverse.

    Q.Briefly explain the shock absorber in suspension system.

    Let's start our discussion of shock absorbers with one of very important point: despite

    what many people think, conventional shock absorbers do not support vehicle weight.

    Instead, the primary purpose of the shock absorber is to control spring and

    suspension movement. This is accomplished by turning the kinetic energy of

    suspension movement into thermal energy, or heat energy, to be dissipated through

    the hydraulic fluid.

    Shock absorbers are basically oil pumps. A piston is attached to the end of the piston

    rod and works against hydraulic fluid in the pressure tube. As the suspension travels

    up and down, the hydraulic fluid is forced through tiny holes, called orifices, inside

    the piston. However, these orifices let only a small amount of fluid through the

    piston. This slows down the piston, which in turn slows down spring and suspension


  • Prepared by: Kartik Suthar

    The amount of resistance a shock absorber develops depends on the speed of the

    suspension and the number and size of the orifices in the piston. All modern shock

    absorbers are velocity sensitive hydraulic damping devices - meaning the faster the

    suspension moves, the more resistance the shock absorber provides. Because of this

    feature, shock absorbers adjust to road condi