Understanding the Drive Layouts
Alvin D. Agomaa
February 13, 2006
The drive layout is the arrangement of the engine, transmission, and driven axles. The types of drive layouts are Front engine Front wheel drive (FF/ FWD), Front engine Rear wheel drive (FR/RWD), Mid engine Rear wheel drive(MR), Rear engine Rear wheel drive(RR), Four wheel drive (4WD or 4x4) and the All Wheel Drive(AWD). Each of these layouts has their own performance, advantages and disadvantages.
Front engine Front wheel drive (FF/FWD) – The Engine and the two driven axles are placed in front, where the power from the engine is transferred straight to the front wheels. This layout increases the interior space especially in small cars because there is no central tunnel needed for the driveshaft. FF layout has advantage when it comes on low grip surfaces, and its tendency to understeer reduces the risk of losing control. The disadvantage is the load placed on the front tires. The front tires must transfer all acceleration, steering, cornering, and braking forces to the road. This kind of tasks gives a lot of stress in front tires which may lead to wear and tear, while the rear tires have very little load on them.
Front engine Rear wheel drive (FR/ RWD) - This is the complement of FF layout, where the engine is placed longitudinally at the front but the two driven axles are placed at the rear connected through the driveshaft. With this kind of layout, installation of more powerful engine such as V8, V10 and V12 is not a problem. Since the FR has a driveshaft, central tunnel is present in this layout a little interior space is sacrificed. All of the disadvantages of the FF layout are the advantages of FR layout. Mid Engine Rear wheel drive (MR) – The drive layout that consumes a lot of interior space of the car especially the seating capacity, the engine is placed in the middle of the chassis and the driven axles are at the rear. Although it has more weight at the rear, entering a corner makes it more difficult because the front tires have less traction resulting to understeer and since the rear is heavy, the car tends to oversteer when exiting a corner. This kind of layout is commonly used in racing cars and sports cars because of weight distribution focused in the center of the car.
Rear engine Rear wheel drive (RR) - This layout places both engine and the driven axle at the rear of the vehicle, even though the rear wheels benefit from the additional grip due to the added weight given by the engine, the front wheels still need grip in order to steer the car effectively. That’s why RR layout car can also be prone to understeer. Four Wheel Drive (4WD or 4X4) / All Wheel Drive (AWD) – It is a term usually used to describe a car where the four wheels receive power from the engine simultaneously. This can be found in an off-road vehicle. A well distributed power to the four wheels improves the grip of the vehicle. The terms 4WD and 4X4 are used in jeeps and other off-road vehicles that require the driver to switch from 2WD used in street driving (two wheel drive) to 4WD to improve the grip depending on the road condition like mud, snow, etc. and it has a high and low gear selection. The AWD term was invented to identify the vehicle capable of driving all the wheels on any road condition without selecting high and low gear selection because the power is distributed on all the wheels. Unlike the 4WD with gear selection, you don’t have to select the appropriate gear to match the road condition. Most of the modern cars use AWD system for more traction and better handling.
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