What's Best For Towing?

Photo of a truck towing a boat out of the water

Two-Wheel, All-Wheel, or Four-Wheel Drive

When considering a tow vehicle, what are the advantages and disadvantages of all-wheel drive (AWD) versus two-wheel drive (2WD) or four-wheel drive (4WD)? What makes AWD and 4WD different, and how does each system work for towing? At the end of the day, if all three systems are available on a tow vehicle you're considering, which should you choose? To start, it helps to know a little about each system and how it works.

Two-Wheel Drive

Two-wheel drive includes both rear-wheel drive (RWD) and front-wheel drive (FWD) systems. The most common and inexpensive drive systems are also the simplest. A shaft from the transmission drives a gear in the differential (or transaxle) that in turn drives two wheels (either front or rear). Front-wheel-drive vehicles generally have better performance in slippery or rough conditions than rear-wheel drive for two reasons: First, the engine and transmission are positioned directly over the front wheels, adding weight over the tires for better traction. Second, the wheels are pulling the vehicle along rather than pushing it, providing a better mechanical advantage.

Photo of a truck towing a boat out of the water

Four-Wheel Drive

In a 4WD drivetrain, the output shaft from the transmission goes into a transfer case where the engine power splits between front and rear driveshafts. When the driver selects 2WD by moving a lever or turning a knob on the dash, the rear driveshaft turns a gear inside the rear differential that turns each wheel. When the driver selects 4H (high) or 4L (low), the front axle is also engaged, turning the front wheels. 4WD typically has to be manually engaged, so it's called a part-time 4WD system. There are some vehicles with permanent 4WD. This is a basic explanation of how 4WD works; it's actually a bit more complicated, especially now with computer-controlled 4WD systems. 4WD systems also have a dedicated transfer case with a separate low-range gear that multiplies the transmission gearing to provide for a much lower gear ratio, with the result being more power for each tire on wet or rough surfaces.

Some more expensive 4WD systems also offer AWD or 2WD settings. Usually, they operate in AWD or 2WD in normal operating conditions. In today's systems, computers constantly determine the optimum amount of traction the front and rear wheels need and adjust to deliver the engine's power accordingly. So, if one or more wheels are slipping, the computer automatically sends more power to the other wheels to compensate and aid the vehicle in maintaining control.

Traditional 4WD systems can add several hundred pounds and significantly reduce fuel economy. Other drawbacks include higher initial vehicle cost and added maintenance costs.

All-Wheel Drive

All-wheel drive is on-demand traction control that intermittently sends power to the non-primary-powered wheels. Most vehicles use a FWD system with an added differential inside the transmission or in a separate housing. AWD sends power through a shaft to a rear differential; power is then directed to each of the rear wheels. In some models, a certain percentage of engine power is sent to the rear wheels until the computer sensor detects front wheel slip and redirects more power.

Although this type of system doesn't offer an extra low-range gear, it does provide significantly better traction than FWD in slippery conditions because the AWD's computer system detects and compensates for wheel slip between front and rear wheels. The majority of AWD systems are not considered as capable as "true" 4WD systems. It's a common perception that AWD is not as hard-core as 4WD and should only be used for "all weather" driving, while 4WD can be used for "all condition" — including off road — driving. This is true to some extent, due in large part to the extra capability that the 4L gear selection gives 4WD systems — a feature that AWD systems do not offer. 

— Published: Summer 2013

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