I mean like Subaru's, which have 4 wheels, yet say they have "all wheel drive"
All wheel drive (AWD) is when there is a center differential. I'm assuming you know what a differential is like on the back of a pickup. So ya know how with an open rear diff if one wheel has more traction the other one will get the power, it's the same thing here, the diff in the center of an AWD vehicle such as a Subaru is open. It's literally just a diff rotated to have the two axles going to the front and rear diff to give them power. But let's say the front wheels are on ice and the rears are on dry pavement, the front wheels will spin because tey have the least amount of traction. But with 4 wheel drive (4x4) or (4wd) there is no center diff, but a transfer case which is controlled usually by a shifter inside the car that lets you choose where all the power is going. So in 2wd, all the power will usually go to the rear wheels, but in 4wd mode, it is just like locking that center diff in the AWD. So the front wheels can't spin faster or slower than the rear wheels. Hope i helped!
All wheel drive is a system that provides power to all whells all the time. it cannot be disengaged. 4 whell drive typically is used in truck and comercial aplications or rugged SUVs. 4WD can be disengaged or selected at the client needs. Typical SUVs like Acura, Subaru, Mercede-Benz, are All wheel drive.
The difference is how power is distributed to the wheels. All-wheel drive allows the torque to be applied to each wheel independently, and usually is always on. It allows a sophisticated computer system to allocate power to each wheel to maximize traction and steering. AWD is best for traction control on roads, and is not particularly useful for hardcore offroading/mudding. 4-wheel drive, however, typically ties all wheels together (called a limited-slip differential), and you can typically disengage/re-engage it. It works well for offroading, but isn't very effective on highways.
All wheel means the four wheel drive in on all the time. 4 wheel means it is usually two wheel until the driver selects 4 wheel.
My wife's Honda CR-V was AWD and it was little better than front wheel drive. The rear wheels only engaged (slightly) after the front wheels spun for a long time. We traded for a Hyundai Santa Fe that was 4WD. It is amazing. The front wheels never get the chance to spin. Then you have 4X4 like my Ford Ranger pickup. When you put it in 4X4 and make a sharp turn the wheels skid and hop up and down because they all have full power all the time. The driver selects between 2X4, 4X4 high range and 4X4 low range. I love the low range for pulling my trailer out into the field or driving on jeep roads. On extreme driving it does the best. But, I do like the 4WD of the Santa Fe for daily driving, snow, etc..
