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Its a debate nearly as old as the automobile itself, but didnt really come to light in the public mind until the late 1980s and early 1990s. While rear-wheel drive was originally a concession to simplicity, later manufacturing methods would give front-drive an edge where engineering costs were concerned. All-wheel drive would seem to combine the best of both worlds, but it, too, comes with a few provisos.

Drive Layout

Rear wheel drive vehicles typically use a longitudinal (front-to-back) engine and transmission arrangement that sends power to the rear wheels. Front-drivers typically use a laterally (side-to-side) oriented engine and transaxle that sends power to the front steering wheels. All wheel drive vehicles based on front-drivers (like the Mitsubishi Lancer Evolution) typically use a transaxle with an additional rear-facing output shaft that sends power to the rear axle as well as the front. AWD cars based on RWD counterparts (like the Chrysler 300C AWD) generally use a transfer case bolted to the back of the transmission like a 4WD vehicle would.

AWD vs. 4WD -- Whats the Difference?

A 4WD truck uses a transfer case that solidly locks the front and rear axles together. A 4WD system always splits power evenly; 50 percent to the front and 50 percent to the rear. An AWD system uses a differential similar to the limited-slip differentials used in the axles of many performance cars. Generally speaking, these limited-slip center differentials use a viscous-coupling design that uses a sticky fluid to transfer power from the input shaft to either of the axles. The center differential defaults to either the front (i.e. Lancer Evo) or rear (i.e. Lamborghini Murcielago) axle, engaging the other axle only when the computer detects tire slippage at the default axle.

FWD Advantages

Prior to the 1980s, front-wheel drive was thought of as the be-all-end-all of drivetrains. It offered directional stability, made the car practically impossible to spin, didnt require a space-hogging transmission tunnel inside the cars cabin and was cheaper to produce. This remains as true today as it ever was, especially where production costs and interior room are concerned.

RWD Advantages

The high-powered engines that debuted during Reagans tenure brought to light one glaring fault in the FWD design: a single pair of tires could steer the car, or they could accelerate it, but they couldnt do both at the same time. This means that a FWDs front tires will lose traction when accelerating out of a corner, causing massive under-steer or "push." Applying the throttle while cornering in a RWD car causes the chassis to rotate around the cars center. allowing the driver to adjust the vehicles orientation in mid-corner in order to maintain the intended path.

AWD Advantages

AWD cars are all about traction and power delivery. The AWD systems viscous-coupling differential allows the computer to send power to whichever axle currently has the most traction, which means that an AWD car will always try to go wherever the steering wheel is pointed. Consequently, an AWD car can use a much more powerful engine without fear that the power will go to waste.

Comparison

FWD is the drivetrain of choice if all you care about is getting from point A to point B in relative comfort and efficiency. RWD is for those who enjoy the dynamics of driving, of mastering vehicle control by careful and balanced application of throttle and steering input. AWD is the most versatile of all drivetrains, offering Velcro traction, predictable steering response and consistent performance. However, AWD systems do add some weight, cost a bit of fuel economy and are arguably less rewarding to drive than a good RWD car. In short, AWD is safer and technically "better," but RWD is more fun.

Automotive repairs often require exact settings when tightening fasteners to ensure that parts are properly fastened. The various bolts and fasteners used to assemble an automobile have different tensile strengths, and stresses produced by operation of the vehicle require these fasteners to accommodate these stresses without failing. To place the proper tension on a fastener without exceeding its tensile strength, different types of torque wrenches are used when tightening them.

Digital Torque Wrench

Digital torque wrenches use an electronic display to show the amount of torque applied with the wrench. These wrenches are usually switched between metric measurements and SAE measurements and are also easily set to display torque in either foot pound or inch pound increments. The displays on the wrenches are electrically powered and use either an LCD or LED display screen mounted on the handle to show torque numbers.

Clicker Torque Wrench

Clicker torque wrenches signal when the desired amount of torque is reached by emitting an audible click. These wrenches include a spring inside the handle that places a load on an internal lever. The amount of tension in the spring is adjusted by turning the sleeve on the bottom of the handle to the desired torque level indicated on the handle. When the proper amount of torque is applied, the force applied to the wrench overcomes the spring-loaded lever within the handle, causing it to emit an audible click as it releases. Because these wrenches use a spring to preload an internal lever, you reset them back to zero after each use because prolonged compression of the spring degrades the strength of the spring and reduces the wrenchs accuracy.

Beam Wrench

Beam torque wrenches are the most common type of torque wrench. They have a long pointer beam mounted parallel to the handle shaft. When torque is applied to a bolt, the handle shaft bends but the pointer beam remains straight. The end of the pointer beam then matches up to an indicator mounted to the handle shaft, which shows how much torque is applied. You must observe the indicator on these wrenches from a straight-on view to accurately read the torque readings.

Dial Indicator Torque Wrench

Dial indicator torque wrenches operate similarly to beam-style torque wrenches. Instead of having a separate pointer beam over an indicator mounted on the handle, the beam is enclosed within a housing and moves the indicator on a dial as torque is applied. The dial indicator is easier to read than the indicator on the beam wrench and some dial indicator wrenches include lights or buzzers to indicate when the desired torque setting is reached.