TRANSMISSIONS + DRIVETRAINS

Here Is What Those Acronyms Mean

FWD - Front Wheel Drive is the standard configuration for the majority of today's cars. FWD means the engine is mounted cross wise in the front of the car, and power goes through the transmission directly to the front wheels only. If you wish to improve your traction in winter driving, the snow tires go on the front wheels. Snow chains are probably not a good idea, as when you turn sharply they may do damage to the body as clearances will decrease in a tight turn.

RWD - Rear Wheel Drive isn't encountered very often, although BMW is famous for it.  RWD means the power is delivered to the rear wheels only.  Drivers comment that RWD does deliver better "road-feel" although at the expense of substantial losses in traction.

AWD- All Wheel Drive can come in two formats. Subaru is a true AWD in that it is always suppling power to all wheels. Many other brands and models operate the same way, as power goes through the transmission and is directed both to the front and rear. The AWD system usually does NOT have lockouts at the wheels, so it always supplies power to all wheels. You get less mileage from AWD than with a FWD or RWD vehicle, as you are always turning the whole the drive train whether you need it or not. 

Some newer vehicles operate by usually being in front wheel drive, and at the flip of a switch can engage the rear wheels, making it an AWD system. This will be more economical to drive (better gas mileage), as the rear wheels aren't turning all the time.

AWD is different from 4WD in that it can be used on dry pavement without destroying the drivetrain.  AWD can do this because it uses a central differential which allows each tire to rotate at a different speed.  By doing so driveline binding, wheel hop, and other issues associated with the use of 4WD on dry pavement are avoided.

Identical drivetrain systems are commonly marketed under different names for branding and, conversely, different drivetrain systems are commonly marketed under the same name for brand uniformity. Audi's quattro, DaimlerChrysler's 4Matic used on Mercedes-Benz products, BMW with the xDrive, and Volkswagen's 4motion, for example, can mean either an automatically-engaging "on-demand" system with a Haldex Traction clutch, or a continuously-operating permanent 4WD system with a Torsen (torque-sensing) differential.

4X2 (or 2WD) - Four By Two is usually used in relation to a 2-wheel drive pickup, or SUV.  It means is the power goes from the engine, through the transmission, directly to the rear axle and wheels. If you place one rear wheel on ice it will spin and the other rear wheel will not get any power. A limited slip differential (traction control) is an improvement as it helps shift some power to the non-spinning wheel.  Real-world experience is that it is only moderately effective in getting you out of a wheel spinning situation.

4x2 is the standard drive arrangement going back to the beginning of the automobile. Hence the reason Dad always put snow tires on the rear wheels in the winter. Today this system is usually reserved for pickup trucks, SUV's and some large cars - although don't count on many large cars being 4x2 configuration any more, as today most are front wheel drive.

The advantages of a 4x2 vs. a 4x4 are:

• a smoother, quieter ride
• better handling and smaller turning radius
• better fuel economy and acceleration due to less weight and wind resistance
• is almost always less expensive to buy and to service (warranty companies charge a premium to cover 4x4)
• a vehicle which is usually a couple of inches lower, making it easier to get in an out of and giving it better road feel due to its lower center of gravity

4X4 (or 4WD) - Four By Four is a true 4-wheel drive vehicle. The 4x4 means all four wheels can receive power and torque simultaneously. This type of system is usually found in pickup trucks, and large SUV's. You will usually find an extra lever in the cab, or a switch on the dash to take the vehicle in and out of four wheel drive. When in 4x4 mode, power from the engine goes through the transmission and on to a transfer case. This is a gear box that divides the power, sending it both the rear and front axles. The transfer case may also have a low range as well as the high range you will use during normal driving.

The advantages of a 4x4 vs. a 4x2 are:

• If you go "off-road" you will get stuck less
• 4x4's tend to enjoy higher resale values as traditionally the "looks" of the 4x4 are stronger
• If you live somewhere that gets a lot of rain, snow or ice, you should get a 4x4