AWD vs. 4WD

A while back (September 2015) I talked about the difference between all-wheel drive (AWD) and four-wheel drive (4WD). But I got one important thing wrong. More on that in a moment.

There are basically four different types of drives on cars/trucks/SUVs. First is rear-wheel drive (RWD). This is when the power of the engine goes to the rear wheels only. This is usually true for sports cars and trucks that don't have four-wheel drive. The advantage of RWD is responsiveness in spirited driving. The disadvantage is it costs more than front-wheel drive and is more complicated. And you have a hump in your passenger compartment floor for the drive axle. 

Second is front-wheel drive (FWD). FWD is on a lot of cars, some SUVs, and a lot of crossovers. Advantages are simplicity (the engine is right over the drive tires), less weight, and a flat floor in the passenger compartment. Disadvantages are torque steer with high power cars, and front tires wear out faster because they do a lot of the work (steering, powering, and braking the car).

Third is all-wheel drive (AWD). This is when all the wheels are driven all the time. Advantages are better grip in nearly all situations. Disadvantages are cost and weight and complexity (more things to break). Because of more weight, your gas mileage will suffer.

There are all sorts of different AWD systems which vary by manufacture. Some send 25% of the engine power to each wheel no mater what. Some send more power to tires that have better grip. Some send more to the rear tires to simulate RWD.

Finally, is four-wheel drive (4WD). This is exclusively on trucks and SUVs. The important thing I got wrong is this: you can't drive 4WD in four wheel drive on dry pavement. The whole system will bind. Nor on wet pavement. Snowy pavement is okay. So these systems can be turned on and off.

The reason you can't drive 4WD on pavement is the axles are locked. So when you go around a corner the inside tire turns the same speed as the outside tire. On dirt or snow this isn't a problem. But on dry or wet pavement, it will cause your driveline to bind. So take your 4WD vehicle out of four-wheel drive before getting on dry pavement. When not in four-wheel drive, 4WD vehicles are almost universally rear-drive (I can't think of one that isn't).

Which drive system you get depends on what you think you need. For most people FWD or RWD is sufficient. A good set of snow tires makes a FWD or RWD perform in snow often better than an AWD with all-season tires. An AWD vehicle with good snow tires will perform very well in snow.